Revision: 1282
http://www.exim.org/viewvc/pcre2?view=rev&revision=1282
Author: ph10
Date: 2020-11-04 17:01:13 +0000 (Wed, 04 Nov 2020)
Log Message:
-----------
Documentation update
Modified Paths:
--------------
code/trunk/doc/html/pcre2api.html
code/trunk/doc/pcre2.txt
code/trunk/doc/pcre2api.3
Modified: code/trunk/doc/html/pcre2api.html
===================================================================
--- code/trunk/doc/html/pcre2api.html 2020-11-03 13:20:09 UTC (rev 1281)
+++ code/trunk/doc/html/pcre2api.html 2020-11-04 17:01:13 UTC (rev 1282)
@@ -626,14 +626,15 @@
<P>
In a more complicated situation, where patterns are compiled only when they are
first needed, but are still shared between threads, pointers to compiled
-patterns must be protected from simultaneous writing by multiple threads, at
-least until a pattern has been compiled. The logic can be something like this:
+patterns must be protected from simultaneous writing by multiple threads. This
+is somewhat tricky to do correctly. If you know that writing to a pointer is
+atomic in your environment, you can use logic like this:
<pre>
Get a read-only (shared) lock (mutex) for pointer
if (pointer == NULL)
{
Get a write (unique) lock for pointer
- pointer = pcre2_compile(...
+ if (pointer == NULL) pointer = pcre2_compile(...
}
Release the lock
Use pointer in pcre2_match()
@@ -641,10 +642,39 @@
Of course, testing for compilation errors should also be included in the code.
</P>
<P>
-If JIT is being used, but the JIT compilation is not being done immediately,
-(perhaps waiting to see if the pattern is used often enough) similar logic is
-required. JIT compilation updates a pointer within the compiled code block, so
-a thread must gain unique write access to the pointer before calling
+The reason for checking the pointer a second time is as follows: Several
+threads may have acquired the shared lock and tested the pointer for being
+NULL, but only one of them will be given the write lock, with the rest kept
+waiting. The winning thread will compile the pattern and store the result.
+After this thread releases the write lock, another thread will get it, and if
+it does not retest pointer for being NULL, will recompile the pattern and
+overwrite the pointer, creating a memory leak and possibly causing other
+issues.
+</P>
+<P>
+In an environment where writing to a pointer may not be atomic, the above logic
+is not sufficient. The thread that is doing the compiling may be descheduled
+after writing only part of the pointer, which could cause other threads to use
+an invalid value. Instead of checking the pointer itself, a separate "pointer
+is valid" flag (that can be updated atomically) must be used:
+<pre>
+ Get a read-only (shared) lock (mutex) for pointer
+ if (!pointer_is_valid)
+ {
+ Get a write (unique) lock for pointer
+ if (!pointer_is_valid)
+ {
+ pointer = pcre2_compile(...
+ pointer_is_valid = TRUE
+ }
+ }
+ Release the lock
+ Use pointer in pcre2_match()
+</pre>
+If JIT is being used, but the JIT compilation is not being done immediately
+(perhaps waiting to see if the pattern is used often enough), similar logic is
+required. JIT compilation updates a value within the compiled code block, so a
+thread must gain unique write access to the pointer before calling
<b>pcre2_jit_compile()</b>. Alternatively, <b>pcre2_code_copy()</b> or
<b>pcre2_code_copy_with_tables()</b> can be used to obtain a private copy of the
compiled code before calling the JIT compiler.
@@ -3959,7 +3989,7 @@
</P>
<br><a name="SEC42" href="#TOC1">REVISION</a><br>
<P>
-Last updated: 05 October 2020
+Last updated: 04 November 2020
<br>
Copyright © 1997-2020 University of Cambridge.
<br>
Modified: code/trunk/doc/pcre2.txt
===================================================================
--- code/trunk/doc/pcre2.txt 2020-11-03 13:20:09 UTC (rev 1281)
+++ code/trunk/doc/pcre2.txt 2020-11-04 17:01:13 UTC (rev 1282)
@@ -683,77 +683,107 @@
In a more complicated situation, where patterns are compiled only when
they are first needed, but are still shared between threads, pointers
to compiled patterns must be protected from simultaneous writing by
- multiple threads, at least until a pattern has been compiled. The logic
- can be something like this:
+ multiple threads. This is somewhat tricky to do correctly. If you know
+ that writing to a pointer is atomic in your environment, you can use
+ logic like this:
Get a read-only (shared) lock (mutex) for pointer
if (pointer == NULL)
{
Get a write (unique) lock for pointer
- pointer = pcre2_compile(...
+ if (pointer == NULL) pointer = pcre2_compile(...
}
Release the lock
Use pointer in pcre2_match()
- Of course, testing for compilation errors should also be included in
+ Of course, testing for compilation errors should also be included in
the code.
+ The reason for checking the pointer a second time is as follows: Sev-
+ eral threads may have acquired the shared lock and tested the pointer
+ for being NULL, but only one of them will be given the write lock, with
+ the rest kept waiting. The winning thread will compile the pattern and
+ store the result. After this thread releases the write lock, another
+ thread will get it, and if it does not retest pointer for being NULL,
+ will recompile the pattern and overwrite the pointer, creating a memory
+ leak and possibly causing other issues.
+
+ In an environment where writing to a pointer may not be atomic, the
+ above logic is not sufficient. The thread that is doing the compiling
+ may be descheduled after writing only part of the pointer, which could
+ cause other threads to use an invalid value. Instead of checking the
+ pointer itself, a separate "pointer is valid" flag (that can be updated
+ atomically) must be used:
+
+ Get a read-only (shared) lock (mutex) for pointer
+ if (!pointer_is_valid)
+ {
+ Get a write (unique) lock for pointer
+ if (!pointer_is_valid)
+ {
+ pointer = pcre2_compile(...
+ pointer_is_valid = TRUE
+ }
+ }
+ Release the lock
+ Use pointer in pcre2_match()
+
If JIT is being used, but the JIT compilation is not being done immedi-
- ately, (perhaps waiting to see if the pattern is used often enough)
- similar logic is required. JIT compilation updates a pointer within the
- compiled code block, so a thread must gain unique write access to the
- pointer before calling pcre2_jit_compile(). Alternatively,
- pcre2_code_copy() or pcre2_code_copy_with_tables() can be used to ob-
- tain a private copy of the compiled code before calling the JIT com-
+ ately (perhaps waiting to see if the pattern is used often enough),
+ similar logic is required. JIT compilation updates a value within the
+ compiled code block, so a thread must gain unique write access to the
+ pointer before calling pcre2_jit_compile(). Alternatively,
+ pcre2_code_copy() or pcre2_code_copy_with_tables() can be used to ob-
+ tain a private copy of the compiled code before calling the JIT com-
piler.
Context blocks
- The next main section below introduces the idea of "contexts" in which
+ The next main section below introduces the idea of "contexts" in which
PCRE2 functions are called. A context is nothing more than a collection
of parameters that control the way PCRE2 operates. Grouping a number of
parameters together in a context is a convenient way of passing them to
- a PCRE2 function without using lots of arguments. The parameters that
- are stored in contexts are in some sense "advanced features" of the
+ a PCRE2 function without using lots of arguments. The parameters that
+ are stored in contexts are in some sense "advanced features" of the
API. Many straightforward applications will not need to use contexts.
In a multithreaded application, if the parameters in a context are val-
- ues that are never changed, the same context can be used by all the
+ ues that are never changed, the same context can be used by all the
threads. However, if any thread needs to change any value in a context,
it must make its own thread-specific copy.
Match blocks
- The matching functions need a block of memory for storing the results
+ The matching functions need a block of memory for storing the results
of a match. This includes details of what was matched, as well as addi-
- tional information such as the name of a (*MARK) setting. Each thread
+ tional information such as the name of a (*MARK) setting. Each thread
must provide its own copy of this memory.
PCRE2 CONTEXTS
- Some PCRE2 functions have a lot of parameters, many of which are used
- only by specialist applications, for example, those that use custom
- memory management or non-standard character tables. To keep function
- argument lists at a reasonable size, and at the same time to keep the
- API extensible, "uncommon" parameters are passed to certain functions
- in a context instead of directly. A context is just a block of memory
- that holds the parameter values. Applications that do not need to ad-
+ Some PCRE2 functions have a lot of parameters, many of which are used
+ only by specialist applications, for example, those that use custom
+ memory management or non-standard character tables. To keep function
+ argument lists at a reasonable size, and at the same time to keep the
+ API extensible, "uncommon" parameters are passed to certain functions
+ in a context instead of directly. A context is just a block of memory
+ that holds the parameter values. Applications that do not need to ad-
just any of the context parameters can pass NULL when a context pointer
is required.
- There are three different types of context: a general context that is
- relevant for several PCRE2 operations, a compile-time context, and a
+ There are three different types of context: a general context that is
+ relevant for several PCRE2 operations, a compile-time context, and a
match-time context.
The general context
- At present, this context just contains pointers to (and data for) ex-
- ternal memory management functions that are called from several places
- in the PCRE2 library. The context is named `general' rather than
- specifically `memory' because in future other fields may be added. If
- you do not want to supply your own custom memory management functions,
- you do not need to bother with a general context. A general context is
+ At present, this context just contains pointers to (and data for) ex-
+ ternal memory management functions that are called from several places
+ in the PCRE2 library. The context is named `general' rather than
+ specifically `memory' because in future other fields may be added. If
+ you do not want to supply your own custom memory management functions,
+ you do not need to bother with a general context. A general context is
created by:
pcre2_general_context *pcre2_general_context_create(
@@ -760,7 +790,7 @@
void *(*private_malloc)(PCRE2_SIZE, void *),
void (*private_free)(void *, void *), void *memory_data);
- The two function pointers specify custom memory management functions,
+ The two function pointers specify custom memory management functions,
whose prototypes are:
void *private_malloc(PCRE2_SIZE, void *);
@@ -768,16 +798,16 @@
Whenever code in PCRE2 calls these functions, the final argument is the
value of memory_data. Either of the first two arguments of the creation
- function may be NULL, in which case the system memory management func-
- tions malloc() and free() are used. (This is not currently useful, as
- there are no other fields in a general context, but in future there
- might be.) The private_malloc() function is used (if supplied) to ob-
- tain memory for storing the context, and all three values are saved as
+ function may be NULL, in which case the system memory management func-
+ tions malloc() and free() are used. (This is not currently useful, as
+ there are no other fields in a general context, but in future there
+ might be.) The private_malloc() function is used (if supplied) to ob-
+ tain memory for storing the context, and all three values are saved as
part of the context.
- Whenever PCRE2 creates a data block of any kind, the block contains a
- pointer to the free() function that matches the malloc() function that
- was used. When the time comes to free the block, this function is
+ Whenever PCRE2 creates a data block of any kind, the block contains a
+ pointer to the free() function that matches the malloc() function that
+ was used. When the time comes to free the block, this function is
called.
A general context can be copied by calling:
@@ -789,13 +819,13 @@
void pcre2_general_context_free(pcre2_general_context *gcontext);
- If this function is passed a NULL argument, it returns immediately
+ If this function is passed a NULL argument, it returns immediately
without doing anything.
The compile context
- A compile context is required if you want to provide an external func-
- tion for stack checking during compilation or to change the default
+ A compile context is required if you want to provide an external func-
+ tion for stack checking during compilation or to change the default
values of any of the following compile-time parameters:
What \R matches (Unicode newlines or CR, LF, CRLF only)
@@ -805,11 +835,11 @@
The maximum length of the pattern string
The extra options bits (none set by default)
- A compile context is also required if you are using custom memory man-
- agement. If none of these apply, just pass NULL as the context argu-
+ A compile context is also required if you are using custom memory man-
+ agement. If none of these apply, just pass NULL as the context argu-
ment of pcre2_compile().
- A compile context is created, copied, and freed by the following func-
+ A compile context is created, copied, and freed by the following func-
tions:
pcre2_compile_context *pcre2_compile_context_create(
@@ -820,7 +850,7 @@
void pcre2_compile_context_free(pcre2_compile_context *ccontext);
- A compile context is created with default values for its parameters.
+ A compile context is created with default values for its parameters.
These can be changed by calling the following functions, which return 0
on success, or PCRE2_ERROR_BADDATA if invalid data is detected.
@@ -827,16 +857,16 @@
int pcre2_set_bsr(pcre2_compile_context *ccontext,
uint32_t value);
- The value must be PCRE2_BSR_ANYCRLF, to specify that \R matches only
- CR, LF, or CRLF, or PCRE2_BSR_UNICODE, to specify that \R matches any
+ The value must be PCRE2_BSR_ANYCRLF, to specify that \R matches only
+ CR, LF, or CRLF, or PCRE2_BSR_UNICODE, to specify that \R matches any
Unicode line ending sequence. The value is used by the JIT compiler and
- by the two interpreted matching functions, pcre2_match() and
+ by the two interpreted matching functions, pcre2_match() and
pcre2_dfa_match().
int pcre2_set_character_tables(pcre2_compile_context *ccontext,
const uint8_t *tables);
- The value must be the result of a call to pcre2_maketables(), whose
+ The value must be the result of a call to pcre2_maketables(), whose
only argument is a general context. This function builds a set of char-
acter tables in the current locale.
@@ -843,22 +873,22 @@
int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
uint32_t extra_options);
- As PCRE2 has developed, almost all the 32 option bits that are avail-
- able in the options argument of pcre2_compile() have been used up. To
- avoid running out, the compile context contains a set of extra option
- bits which are used for some newer, assumed rarer, options. This func-
- tion sets those bits. It always sets all the bits (either on or off).
- It does not modify any existing setting. The available options are de-
+ As PCRE2 has developed, almost all the 32 option bits that are avail-
+ able in the options argument of pcre2_compile() have been used up. To
+ avoid running out, the compile context contains a set of extra option
+ bits which are used for some newer, assumed rarer, options. This func-
+ tion sets those bits. It always sets all the bits (either on or off).
+ It does not modify any existing setting. The available options are de-
fined in the section entitled "Extra compile options" below.
int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
PCRE2_SIZE value);
- This sets a maximum length, in code units, for any pattern string that
- is compiled with this context. If the pattern is longer, an error is
- generated. This facility is provided so that applications that accept
+ This sets a maximum length, in code units, for any pattern string that
+ is compiled with this context. If the pattern is longer, an error is
+ generated. This facility is provided so that applications that accept
patterns from external sources can limit their size. The default is the
- largest number that a PCRE2_SIZE variable can hold, which is effec-
+ largest number that a PCRE2_SIZE variable can hold, which is effec-
tively unlimited.
int pcre2_set_newline(pcre2_compile_context *ccontext,
@@ -865,46 +895,46 @@
uint32_t value);
This specifies which characters or character sequences are to be recog-
- nized as newlines. The value must be one of PCRE2_NEWLINE_CR (carriage
+ nized as newlines. The value must be one of PCRE2_NEWLINE_CR (carriage
return only), PCRE2_NEWLINE_LF (linefeed only), PCRE2_NEWLINE_CRLF (the
- two-character sequence CR followed by LF), PCRE2_NEWLINE_ANYCRLF (any
- of the above), PCRE2_NEWLINE_ANY (any Unicode newline sequence), or
+ two-character sequence CR followed by LF), PCRE2_NEWLINE_ANYCRLF (any
+ of the above), PCRE2_NEWLINE_ANY (any Unicode newline sequence), or
PCRE2_NEWLINE_NUL (the NUL character, that is a binary zero).
A pattern can override the value set in the compile context by starting
with a sequence such as (*CRLF). See the pcre2pattern page for details.
- When a pattern is compiled with the PCRE2_EXTENDED or PCRE2_EX-
- TENDED_MORE option, the newline convention affects the recognition of
- the end of internal comments starting with #. The value is saved with
- the compiled pattern for subsequent use by the JIT compiler and by the
- two interpreted matching functions, pcre2_match() and
+ When a pattern is compiled with the PCRE2_EXTENDED or PCRE2_EX-
+ TENDED_MORE option, the newline convention affects the recognition of
+ the end of internal comments starting with #. The value is saved with
+ the compiled pattern for subsequent use by the JIT compiler and by the
+ two interpreted matching functions, pcre2_match() and
pcre2_dfa_match().
int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
uint32_t value);
- This parameter adjusts the limit, set when PCRE2 is built (default
- 250), on the depth of parenthesis nesting in a pattern. This limit
- stops rogue patterns using up too much system stack when being com-
- piled. The limit applies to parentheses of all kinds, not just captur-
+ This parameter adjusts the limit, set when PCRE2 is built (default
+ 250), on the depth of parenthesis nesting in a pattern. This limit
+ stops rogue patterns using up too much system stack when being com-
+ piled. The limit applies to parentheses of all kinds, not just captur-
ing parentheses.
int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
int (*guard_function)(uint32_t, void *), void *user_data);
- There is at least one application that runs PCRE2 in threads with very
- limited system stack, where running out of stack is to be avoided at
- all costs. The parenthesis limit above cannot take account of how much
- stack is actually available during compilation. For a finer control,
- you can supply a function that is called whenever pcre2_compile()
- starts to compile a parenthesized part of a pattern. This function can
- check the actual stack size (or anything else that it wants to, of
+ There is at least one application that runs PCRE2 in threads with very
+ limited system stack, where running out of stack is to be avoided at
+ all costs. The parenthesis limit above cannot take account of how much
+ stack is actually available during compilation. For a finer control,
+ you can supply a function that is called whenever pcre2_compile()
+ starts to compile a parenthesized part of a pattern. This function can
+ check the actual stack size (or anything else that it wants to, of
course).
- The first argument to the callout function gives the current depth of
- nesting, and the second is user data that is set up by the last argu-
- ment of pcre2_set_compile_recursion_guard(). The callout function
+ The first argument to the callout function gives the current depth of
+ nesting, and the second is user data that is set up by the last argu-
+ ment of pcre2_set_compile_recursion_guard(). The callout function
should return zero if all is well, or non-zero to force an error.
The match context
@@ -918,10 +948,10 @@
Change the backtracking depth limit
Set custom memory management specifically for the match
- If none of these apply, just pass NULL as the context argument of
+ If none of these apply, just pass NULL as the context argument of
pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match().
- A match context is created, copied, and freed by the following func-
+ A match context is created, copied, and freed by the following func-
tions:
pcre2_match_context *pcre2_match_context_create(
@@ -932,7 +962,7 @@
void pcre2_match_context_free(pcre2_match_context *mcontext);
- A match context is created with default values for its parameters.
+ A match context is created with default values for its parameters.
These can be changed by calling the following functions, which return 0
on success, or PCRE2_ERROR_BADDATA if invalid data is detected.
@@ -940,7 +970,7 @@
int (*callout_function)(pcre2_callout_block *, void *),
void *callout_data);
- This sets up a callout function for PCRE2 to call at specified points
+ This sets up a callout function for PCRE2 to call at specified points
during a matching operation. Details are given in the pcre2callout doc-
umentation.
@@ -948,7 +978,7 @@
int (*callout_function)(pcre2_substitute_callout_block *, void *),
void *callout_data);
- This sets up a callout function for PCRE2 to call after each substitu-
+ This sets up a callout function for PCRE2 to call after each substitu-
tion made by pcre2_substitute(). Details are given in the section enti-
tled "Creating a new string with substitutions" below.
@@ -955,27 +985,27 @@
int pcre2_set_offset_limit(pcre2_match_context *mcontext,
PCRE2_SIZE value);
- The offset_limit parameter limits how far an unanchored search can ad-
- vance in the subject string. The default value is PCRE2_UNSET. The
- pcre2_match() and pcre2_dfa_match() functions return PCRE2_ERROR_NO-
+ The offset_limit parameter limits how far an unanchored search can ad-
+ vance in the subject string. The default value is PCRE2_UNSET. The
+ pcre2_match() and pcre2_dfa_match() functions return PCRE2_ERROR_NO-
MATCH if a match with a starting point before or at the given offset is
not found. The pcre2_substitute() function makes no more substitutions.
- For example, if the pattern /abc/ is matched against "123abc" with an
- offset limit less than 3, the result is PCRE2_ERROR_NOMATCH. A match
- can never be found if the startoffset argument of pcre2_match(),
- pcre2_dfa_match(), or pcre2_substitute() is greater than the offset
+ For example, if the pattern /abc/ is matched against "123abc" with an
+ offset limit less than 3, the result is PCRE2_ERROR_NOMATCH. A match
+ can never be found if the startoffset argument of pcre2_match(),
+ pcre2_dfa_match(), or pcre2_substitute() is greater than the offset
limit set in the match context.
- When using this facility, you must set the PCRE2_USE_OFFSET_LIMIT op-
+ When using this facility, you must set the PCRE2_USE_OFFSET_LIMIT op-
tion when calling pcre2_compile() so that when JIT is in use, different
- code can be compiled. If a match is started with a non-default match
+ code can be compiled. If a match is started with a non-default match
limit when PCRE2_USE_OFFSET_LIMIT is not set, an error is generated.
- The offset limit facility can be used to track progress when searching
- large subject strings or to limit the extent of global substitutions.
- See also the PCRE2_FIRSTLINE option, which requires a match to start
- before or at the first newline that follows the start of matching in
+ The offset limit facility can be used to track progress when searching
+ large subject strings or to limit the extent of global substitutions.
+ See also the PCRE2_FIRSTLINE option, which requires a match to start
+ before or at the first newline that follows the start of matching in
the subject. If this is set with an offset limit, a match must occur in
the first line and also within the offset limit. In other words, which-
ever limit comes first is used.
@@ -984,15 +1014,15 @@
uint32_t value);
The heap_limit parameter specifies, in units of kibibytes (1024 bytes),
- the maximum amount of heap memory that pcre2_match() may use to hold
+ the maximum amount of heap memory that pcre2_match() may use to hold
backtracking information when running an interpretive match. This limit
also applies to pcre2_dfa_match(), which may use the heap when process-
- ing patterns with a lot of nested pattern recursion or lookarounds or
+ ing patterns with a lot of nested pattern recursion or lookarounds or
atomic groups. This limit does not apply to matching with the JIT opti-
- mization, which has its own memory control arrangements (see the
- pcre2jit documentation for more details). If the limit is reached, the
- negative error code PCRE2_ERROR_HEAPLIMIT is returned. The default
- limit can be set when PCRE2 is built; if it is not, the default is set
+ mization, which has its own memory control arrangements (see the
+ pcre2jit documentation for more details). If the limit is reached, the
+ negative error code PCRE2_ERROR_HEAPLIMIT is returned. The default
+ limit can be set when PCRE2 is built; if it is not, the default is set
very large and is essentially "unlimited".
A value for the heap limit may also be supplied by an item at the start
@@ -1000,22 +1030,22 @@
(*LIMIT_HEAP=ddd)
- where ddd is a decimal number. However, such a setting is ignored un-
- less ddd is less than the limit set by the caller of pcre2_match() or,
+ where ddd is a decimal number. However, such a setting is ignored un-
+ less ddd is less than the limit set by the caller of pcre2_match() or,
if no such limit is set, less than the default.
- The pcre2_match() function starts out using a 20KiB vector on the sys-
+ The pcre2_match() function starts out using a 20KiB vector on the sys-
tem stack for recording backtracking points. The more nested backtrack-
- ing points there are (that is, the deeper the search tree), the more
- memory is needed. Heap memory is used only if the initial vector is
+ ing points there are (that is, the deeper the search tree), the more
+ memory is needed. Heap memory is used only if the initial vector is
too small. If the heap limit is set to a value less than 21 (in partic-
- ular, zero) no heap memory will be used. In this case, only patterns
- that do not have a lot of nested backtracking can be successfully pro-
+ ular, zero) no heap memory will be used. In this case, only patterns
+ that do not have a lot of nested backtracking can be successfully pro-
cessed.
- Similarly, for pcre2_dfa_match(), a vector on the system stack is used
- when processing pattern recursions, lookarounds, or atomic groups, and
- only if this is not big enough is heap memory used. In this case, too,
+ Similarly, for pcre2_dfa_match(), a vector on the system stack is used
+ when processing pattern recursions, lookarounds, or atomic groups, and
+ only if this is not big enough is heap memory used. In this case, too,
setting a value of zero disables the use of the heap.
int pcre2_set_match_limit(pcre2_match_context *mcontext,
@@ -1022,79 +1052,79 @@
uint32_t value);
The match_limit parameter provides a means of preventing PCRE2 from us-
- ing up too many computing resources when processing patterns that are
+ ing up too many computing resources when processing patterns that are
not going to match, but which have a very large number of possibilities
- in their search trees. The classic example is a pattern that uses
+ in their search trees. The classic example is a pattern that uses
nested unlimited repeats.
- There is an internal counter in pcre2_match() that is incremented each
- time round its main matching loop. If this value reaches the match
+ There is an internal counter in pcre2_match() that is incremented each
+ time round its main matching loop. If this value reaches the match
limit, pcre2_match() returns the negative value PCRE2_ERROR_MATCHLIMIT.
- This has the effect of limiting the amount of backtracking that can
+ This has the effect of limiting the amount of backtracking that can
take place. For patterns that are not anchored, the count restarts from
- zero for each position in the subject string. This limit also applies
+ zero for each position in the subject string. This limit also applies
to pcre2_dfa_match(), though the counting is done in a different way.
- When pcre2_match() is called with a pattern that was successfully pro-
+ When pcre2_match() is called with a pattern that was successfully pro-
cessed by pcre2_jit_compile(), the way in which matching is executed is
- entirely different. However, there is still the possibility of runaway
- matching that goes on for a very long time, and so the match_limit
- value is also used in this case (but in a different way) to limit how
+ entirely different. However, there is still the possibility of runaway
+ matching that goes on for a very long time, and so the match_limit
+ value is also used in this case (but in a different way) to limit how
long the matching can continue.
The default value for the limit can be set when PCRE2 is built; the de-
- fault default is 10 million, which handles all but the most extreme
- cases. A value for the match limit may also be supplied by an item at
+ fault default is 10 million, which handles all but the most extreme
+ cases. A value for the match limit may also be supplied by an item at
the start of a pattern of the form
(*LIMIT_MATCH=ddd)
- where ddd is a decimal number. However, such a setting is ignored un-
- less ddd is less than the limit set by the caller of pcre2_match() or
+ where ddd is a decimal number. However, such a setting is ignored un-
+ less ddd is less than the limit set by the caller of pcre2_match() or
pcre2_dfa_match() or, if no such limit is set, less than the default.
int pcre2_set_depth_limit(pcre2_match_context *mcontext,
uint32_t value);
- This parameter limits the depth of nested backtracking in
- pcre2_match(). Each time a nested backtracking point is passed, a new
+ This parameter limits the depth of nested backtracking in
+ pcre2_match(). Each time a nested backtracking point is passed, a new
memory "frame" is used to remember the state of matching at that point.
- Thus, this parameter indirectly limits the amount of memory that is
- used in a match. However, because the size of each memory "frame" de-
- pends on the number of capturing parentheses, the actual memory limit
- varies from pattern to pattern. This limit was more useful in versions
+ Thus, this parameter indirectly limits the amount of memory that is
+ used in a match. However, because the size of each memory "frame" de-
+ pends on the number of capturing parentheses, the actual memory limit
+ varies from pattern to pattern. This limit was more useful in versions
before 10.30, where function recursion was used for backtracking.
- The depth limit is not relevant, and is ignored, when matching is done
+ The depth limit is not relevant, and is ignored, when matching is done
using JIT compiled code. However, it is supported by pcre2_dfa_match(),
- which uses it to limit the depth of nested internal recursive function
- calls that implement atomic groups, lookaround assertions, and pattern
+ which uses it to limit the depth of nested internal recursive function
+ calls that implement atomic groups, lookaround assertions, and pattern
recursions. This limits, indirectly, the amount of system stack that is
- used. It was more useful in versions before 10.32, when stack memory
+ used. It was more useful in versions before 10.32, when stack memory
was used for local workspace vectors for recursive function calls. From
- version 10.32, only local variables are allocated on the stack and as
+ version 10.32, only local variables are allocated on the stack and as
each call uses only a few hundred bytes, even a small stack can support
quite a lot of recursion.
- If the depth of internal recursive function calls is great enough, lo-
- cal workspace vectors are allocated on the heap from version 10.32 on-
- wards, so the depth limit also indirectly limits the amount of heap
+ If the depth of internal recursive function calls is great enough, lo-
+ cal workspace vectors are allocated on the heap from version 10.32 on-
+ wards, so the depth limit also indirectly limits the amount of heap
memory that is used. A recursive pattern such as /(.(?2))((?1)|)/, when
- matched to a very long string using pcre2_dfa_match(), can use a great
- deal of memory. However, it is probably better to limit heap usage di-
+ matched to a very long string using pcre2_dfa_match(), can use a great
+ deal of memory. However, it is probably better to limit heap usage di-
rectly by calling pcre2_set_heap_limit().
- The default value for the depth limit can be set when PCRE2 is built;
- if it is not, the default is set to the same value as the default for
- the match limit. If the limit is exceeded, pcre2_match() or
+ The default value for the depth limit can be set when PCRE2 is built;
+ if it is not, the default is set to the same value as the default for
+ the match limit. If the limit is exceeded, pcre2_match() or
pcre2_dfa_match() returns PCRE2_ERROR_DEPTHLIMIT. A value for the depth
- limit may also be supplied by an item at the start of a pattern of the
+ limit may also be supplied by an item at the start of a pattern of the
form
(*LIMIT_DEPTH=ddd)
- where ddd is a decimal number. However, such a setting is ignored un-
- less ddd is less than the limit set by the caller of pcre2_match() or
+ where ddd is a decimal number. However, such a setting is ignored un-
+ less ddd is less than the limit set by the caller of pcre2_match() or
pcre2_dfa_match() or, if no such limit is set, less than the default.
@@ -1102,96 +1132,96 @@
int pcre2_config(uint32_t what, void *where);
- The function pcre2_config() makes it possible for a PCRE2 client to
- find the value of certain configuration parameters and to discover
- which optional features have been compiled into the PCRE2 library. The
+ The function pcre2_config() makes it possible for a PCRE2 client to
+ find the value of certain configuration parameters and to discover
+ which optional features have been compiled into the PCRE2 library. The
pcre2build documentation has more details about these features.
- The first argument for pcre2_config() specifies which information is
+ The first argument for pcre2_config() specifies which information is
required. The second argument is a pointer to memory into which the in-
formation is placed. If NULL is passed, the function returns the amount
- of memory that is needed for the requested information. For calls that
- return numerical values, the value is in bytes; when requesting these
- values, where should point to appropriately aligned memory. For calls
- that return strings, the required length is given in code units, not
+ of memory that is needed for the requested information. For calls that
+ return numerical values, the value is in bytes; when requesting these
+ values, where should point to appropriately aligned memory. For calls
+ that return strings, the required length is given in code units, not
counting the terminating zero.
- When requesting information, the returned value from pcre2_config() is
- non-negative on success, or the negative error code PCRE2_ERROR_BADOP-
- TION if the value in the first argument is not recognized. The follow-
+ When requesting information, the returned value from pcre2_config() is
+ non-negative on success, or the negative error code PCRE2_ERROR_BADOP-
+ TION if the value in the first argument is not recognized. The follow-
ing information is available:
PCRE2_CONFIG_BSR
- The output is a uint32_t integer whose value indicates what character
- sequences the \R escape sequence matches by default. A value of
- PCRE2_BSR_UNICODE means that \R matches any Unicode line ending se-
+ The output is a uint32_t integer whose value indicates what character
+ sequences the \R escape sequence matches by default. A value of
+ PCRE2_BSR_UNICODE means that \R matches any Unicode line ending se-
quence; a value of PCRE2_BSR_ANYCRLF means that \R matches only CR, LF,
or CRLF. The default can be overridden when a pattern is compiled.
PCRE2_CONFIG_COMPILED_WIDTHS
- The output is a uint32_t integer whose lower bits indicate which code
- unit widths were selected when PCRE2 was built. The 1-bit indicates
- 8-bit support, and the 2-bit and 4-bit indicate 16-bit and 32-bit sup-
+ The output is a uint32_t integer whose lower bits indicate which code
+ unit widths were selected when PCRE2 was built. The 1-bit indicates
+ 8-bit support, and the 2-bit and 4-bit indicate 16-bit and 32-bit sup-
port, respectively.
PCRE2_CONFIG_DEPTHLIMIT
- The output is a uint32_t integer that gives the default limit for the
- depth of nested backtracking in pcre2_match() or the depth of nested
- recursions, lookarounds, and atomic groups in pcre2_dfa_match(). Fur-
+ The output is a uint32_t integer that gives the default limit for the
+ depth of nested backtracking in pcre2_match() or the depth of nested
+ recursions, lookarounds, and atomic groups in pcre2_dfa_match(). Fur-
ther details are given with pcre2_set_depth_limit() above.
PCRE2_CONFIG_HEAPLIMIT
- The output is a uint32_t integer that gives, in kibibytes, the default
- limit for the amount of heap memory used by pcre2_match() or
- pcre2_dfa_match(). Further details are given with
+ The output is a uint32_t integer that gives, in kibibytes, the default
+ limit for the amount of heap memory used by pcre2_match() or
+ pcre2_dfa_match(). Further details are given with
pcre2_set_heap_limit() above.
PCRE2_CONFIG_JIT
- The output is a uint32_t integer that is set to one if support for
+ The output is a uint32_t integer that is set to one if support for
just-in-time compiling is available; otherwise it is set to zero.
PCRE2_CONFIG_JITTARGET
- The where argument should point to a buffer that is at least 48 code
- units long. (The exact length required can be found by calling
- pcre2_config() with where set to NULL.) The buffer is filled with a
- string that contains the name of the architecture for which the JIT
- compiler is configured, for example "x86 32bit (little endian + un-
- aligned)". If JIT support is not available, PCRE2_ERROR_BADOPTION is
- returned, otherwise the number of code units used is returned. This is
+ The where argument should point to a buffer that is at least 48 code
+ units long. (The exact length required can be found by calling
+ pcre2_config() with where set to NULL.) The buffer is filled with a
+ string that contains the name of the architecture for which the JIT
+ compiler is configured, for example "x86 32bit (little endian + un-
+ aligned)". If JIT support is not available, PCRE2_ERROR_BADOPTION is
+ returned, otherwise the number of code units used is returned. This is
the length of the string, plus one unit for the terminating zero.
PCRE2_CONFIG_LINKSIZE
The output is a uint32_t integer that contains the number of bytes used
- for internal linkage in compiled regular expressions. When PCRE2 is
- configured, the value can be set to 2, 3, or 4, with the default being
- 2. This is the value that is returned by pcre2_config(). However, when
- the 16-bit library is compiled, a value of 3 is rounded up to 4, and
- when the 32-bit library is compiled, internal linkages always use 4
+ for internal linkage in compiled regular expressions. When PCRE2 is
+ configured, the value can be set to 2, 3, or 4, with the default being
+ 2. This is the value that is returned by pcre2_config(). However, when
+ the 16-bit library is compiled, a value of 3 is rounded up to 4, and
+ when the 32-bit library is compiled, internal linkages always use 4
bytes, so the configured value is not relevant.
The default value of 2 for the 8-bit and 16-bit libraries is sufficient
- for all but the most massive patterns, since it allows the size of the
- compiled pattern to be up to 65535 code units. Larger values allow
- larger regular expressions to be compiled by those two libraries, but
+ for all but the most massive patterns, since it allows the size of the
+ compiled pattern to be up to 65535 code units. Larger values allow
+ larger regular expressions to be compiled by those two libraries, but
at the expense of slower matching.
PCRE2_CONFIG_MATCHLIMIT
The output is a uint32_t integer that gives the default match limit for
- pcre2_match(). Further details are given with pcre2_set_match_limit()
+ pcre2_match(). Further details are given with pcre2_set_match_limit()
above.
PCRE2_CONFIG_NEWLINE
- The output is a uint32_t integer whose value specifies the default
- character sequence that is recognized as meaning "newline". The values
+ The output is a uint32_t integer whose value specifies the default
+ character sequence that is recognized as meaning "newline". The values
are:
PCRE2_NEWLINE_CR Carriage return (CR)
@@ -1201,23 +1231,23 @@
PCRE2_NEWLINE_ANYCRLF Any of CR, LF, or CRLF
PCRE2_NEWLINE_NUL The NUL character (binary zero)
- The default should normally correspond to the standard sequence for
+ The default should normally correspond to the standard sequence for
your operating system.
PCRE2_CONFIG_NEVER_BACKSLASH_C
- The output is a uint32_t integer that is set to one if the use of \C
- was permanently disabled when PCRE2 was built; otherwise it is set to
+ The output is a uint32_t integer that is set to one if the use of \C
+ was permanently disabled when PCRE2 was built; otherwise it is set to
zero.
PCRE2_CONFIG_PARENSLIMIT
- The output is a uint32_t integer that gives the maximum depth of nest-
+ The output is a uint32_t integer that gives the maximum depth of nest-
ing of parentheses (of any kind) in a pattern. This limit is imposed to
- cap the amount of system stack used when a pattern is compiled. It is
- specified when PCRE2 is built; the default is 250. This limit does not
+ cap the amount of system stack used when a pattern is compiled. It is
+ specified when PCRE2 is built; the default is 250. This limit does not
take into account the stack that may already be used by the calling ap-
- plication. For finer control over compilation stack usage, see
+ plication. For finer control over compilation stack usage, see
pcre2_set_compile_recursion_guard().
PCRE2_CONFIG_STACKRECURSE
@@ -1228,30 +1258,30 @@
PCRE2_CONFIG_TABLES_LENGTH
The output is a uint32_t integer that gives the length of PCRE2's char-
- acter processing tables in bytes. For details of these tables see the
+ acter processing tables in bytes. For details of these tables see the
section on locale support below.
PCRE2_CONFIG_UNICODE_VERSION
- The where argument should point to a buffer that is at least 24 code
- units long. (The exact length required can be found by calling
- pcre2_config() with where set to NULL.) If PCRE2 has been compiled
- without Unicode support, the buffer is filled with the text "Unicode
- not supported". Otherwise, the Unicode version string (for example,
- "8.0.0") is inserted. The number of code units used is returned. This
+ The where argument should point to a buffer that is at least 24 code
+ units long. (The exact length required can be found by calling
+ pcre2_config() with where set to NULL.) If PCRE2 has been compiled
+ without Unicode support, the buffer is filled with the text "Unicode
+ not supported". Otherwise, the Unicode version string (for example,
+ "8.0.0") is inserted. The number of code units used is returned. This
is the length of the string plus one unit for the terminating zero.
PCRE2_CONFIG_UNICODE
- The output is a uint32_t integer that is set to one if Unicode support
- is available; otherwise it is set to zero. Unicode support implies UTF
+ The output is a uint32_t integer that is set to one if Unicode support
+ is available; otherwise it is set to zero. Unicode support implies UTF
support.
PCRE2_CONFIG_VERSION
- The where argument should point to a buffer that is at least 24 code
- units long. (The exact length required can be found by calling
- pcre2_config() with where set to NULL.) The buffer is filled with the
+ The where argument should point to a buffer that is at least 24 code
+ units long. (The exact length required can be found by calling
+ pcre2_config() with where set to NULL.) The buffer is filled with the
PCRE2 version string, zero-terminated. The number of code units used is
returned. This is the length of the string plus one unit for the termi-
nating zero.
@@ -1269,15 +1299,15 @@
pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);
- The pcre2_compile() function compiles a pattern into an internal form.
- The pattern is defined by a pointer to a string of code units and a
- length (in code units). If the pattern is zero-terminated, the length
- can be specified as PCRE2_ZERO_TERMINATED. The function returns a
+ The pcre2_compile() function compiles a pattern into an internal form.
+ The pattern is defined by a pointer to a string of code units and a
+ length (in code units). If the pattern is zero-terminated, the length
+ can be specified as PCRE2_ZERO_TERMINATED. The function returns a
pointer to a block of memory that contains the compiled pattern and re-
lated data, or NULL if an error occurred.
- If the compile context argument ccontext is NULL, memory for the com-
- piled pattern is obtained by calling malloc(). Otherwise, it is ob-
+ If the compile context argument ccontext is NULL, memory for the com-
+ piled pattern is obtained by calling malloc(). Otherwise, it is ob-
tained from the same memory function that was used for the compile con-
text. The caller must free the memory by calling pcre2_code_free() when
it is no longer needed. If pcre2_code_free() is called with a NULL ar-
@@ -1284,88 +1314,88 @@
gument, it returns immediately, without doing anything.
The function pcre2_code_copy() makes a copy of the compiled code in new
- memory, using the same memory allocator as was used for the original.
- However, if the code has been processed by the JIT compiler (see be-
- low), the JIT information cannot be copied (because it is position-de-
- pendent). The new copy can initially be used only for non-JIT match-
- ing, though it can be passed to pcre2_jit_compile() if required. If
+ memory, using the same memory allocator as was used for the original.
+ However, if the code has been processed by the JIT compiler (see be-
+ low), the JIT information cannot be copied (because it is position-de-
+ pendent). The new copy can initially be used only for non-JIT match-
+ ing, though it can be passed to pcre2_jit_compile() if required. If
pcre2_code_copy() is called with a NULL argument, it returns NULL.
The pcre2_code_copy() function provides a way for individual threads in
- a multithreaded application to acquire a private copy of shared com-
- piled code. However, it does not make a copy of the character tables
- used by the compiled pattern; the new pattern code points to the same
- tables as the original code. (See "Locale Support" below for details
- of these character tables.) In many applications the same tables are
- used throughout, so this behaviour is appropriate. Nevertheless, there
+ a multithreaded application to acquire a private copy of shared com-
+ piled code. However, it does not make a copy of the character tables
+ used by the compiled pattern; the new pattern code points to the same
+ tables as the original code. (See "Locale Support" below for details
+ of these character tables.) In many applications the same tables are
+ used throughout, so this behaviour is appropriate. Nevertheless, there
are occasions when a copy of a compiled pattern and the relevant tables
- are needed. The pcre2_code_copy_with_tables() provides this facility.
- Copies of both the code and the tables are made, with the new code
- pointing to the new tables. The memory for the new tables is automati-
- cally freed when pcre2_code_free() is called for the new copy of the
- compiled code. If pcre2_code_copy_with_tables() is called with a NULL
+ are needed. The pcre2_code_copy_with_tables() provides this facility.
+ Copies of both the code and the tables are made, with the new code
+ pointing to the new tables. The memory for the new tables is automati-
+ cally freed when pcre2_code_free() is called for the new copy of the
+ compiled code. If pcre2_code_copy_with_tables() is called with a NULL
argument, it returns NULL.
- NOTE: When one of the matching functions is called, pointers to the
+ NOTE: When one of the matching functions is called, pointers to the
compiled pattern and the subject string are set in the match data block
- so that they can be referenced by the substring extraction functions
- after a successful match. After running a match, you must not free a
- compiled pattern or a subject string until after all operations on the
- match data block have taken place, unless, in the case of the subject
- string, you have used the PCRE2_COPY_MATCHED_SUBJECT option, which is
- described in the section entitled "Option bits for pcre2_match()" be-
+ so that they can be referenced by the substring extraction functions
+ after a successful match. After running a match, you must not free a
+ compiled pattern or a subject string until after all operations on the
+ match data block have taken place, unless, in the case of the subject
+ string, you have used the PCRE2_COPY_MATCHED_SUBJECT option, which is
+ described in the section entitled "Option bits for pcre2_match()" be-
low.
- The options argument for pcre2_compile() contains various bit settings
- that affect the compilation. It should be zero if none of them are re-
- quired. The available options are described below. Some of them (in
- particular, those that are compatible with Perl, but some others as
- well) can also be set and unset from within the pattern (see the de-
+ The options argument for pcre2_compile() contains various bit settings
+ that affect the compilation. It should be zero if none of them are re-
+ quired. The available options are described below. Some of them (in
+ particular, those that are compatible with Perl, but some others as
+ well) can also be set and unset from within the pattern (see the de-
tailed description in the pcre2pattern documentation).
- For those options that can be different in different parts of the pat-
- tern, the contents of the options argument specifies their settings at
- the start of compilation. The PCRE2_ANCHORED, PCRE2_ENDANCHORED, and
- PCRE2_NO_UTF_CHECK options can be set at the time of matching as well
+ For those options that can be different in different parts of the pat-
+ tern, the contents of the options argument specifies their settings at
+ the start of compilation. The PCRE2_ANCHORED, PCRE2_ENDANCHORED, and
+ PCRE2_NO_UTF_CHECK options can be set at the time of matching as well
as at compile time.
- Some additional options and less frequently required compile-time pa-
- rameters (for example, the newline setting) can be provided in a com-
+ Some additional options and less frequently required compile-time pa-
+ rameters (for example, the newline setting) can be provided in a com-
pile context (as described above).
If errorcode or erroroffset is NULL, pcre2_compile() returns NULL imme-
- diately. Otherwise, the variables to which these point are set to an
+ diately. Otherwise, the variables to which these point are set to an
error code and an offset (number of code units) within the pattern, re-
spectively, when pcre2_compile() returns NULL because a compilation er-
- ror has occurred. The values are not defined when compilation is suc-
+ ror has occurred. The values are not defined when compilation is suc-
cessful and pcre2_compile() returns a non-NULL value.
- There are nearly 100 positive error codes that pcre2_compile() may re-
- turn if it finds an error in the pattern. There are also some negative
- error codes that are used for invalid UTF strings when validity check-
- ing is in force. These are the same as given by pcre2_match() and
+ There are nearly 100 positive error codes that pcre2_compile() may re-
+ turn if it finds an error in the pattern. There are also some negative
+ error codes that are used for invalid UTF strings when validity check-
+ ing is in force. These are the same as given by pcre2_match() and
pcre2_dfa_match(), and are described in the pcre2unicode documentation.
- There is no separate documentation for the positive error codes, be-
- cause the textual error messages that are obtained by calling the
+ There is no separate documentation for the positive error codes, be-
+ cause the textual error messages that are obtained by calling the
pcre2_get_error_message() function (see "Obtaining a textual error mes-
- sage" below) should be self-explanatory. Macro names starting with
- PCRE2_ERROR_ are defined for both positive and negative error codes in
+ sage" below) should be self-explanatory. Macro names starting with
+ PCRE2_ERROR_ are defined for both positive and negative error codes in
pcre2.h.
The value returned in erroroffset is an indication of where in the pat-
- tern the error occurred. It is not necessarily the furthest point in
+ tern the error occurred. It is not necessarily the furthest point in
the pattern that was read. For example, after the error "lookbehind as-
- sertion is not fixed length", the error offset points to the start of
- the failing assertion. For an invalid UTF-8 or UTF-16 string, the off-
+ sertion is not fixed length", the error offset points to the start of
+ the failing assertion. For an invalid UTF-8 or UTF-16 string, the off-
set is that of the first code unit of the failing character.
- Some errors are not detected until the whole pattern has been scanned;
- in these cases, the offset passed back is the length of the pattern.
- Note that the offset is in code units, not characters, even in a UTF
+ Some errors are not detected until the whole pattern has been scanned;
+ in these cases, the offset passed back is the length of the pattern.
+ Note that the offset is in code units, not characters, even in a UTF
mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char-
acter.
- This code fragment shows a typical straightforward call to pcre2_com-
+ This code fragment shows a typical straightforward call to pcre2_com-
pile():
pcre2_code *re;
@@ -1382,28 +1412,28 @@
Main compile options
- The following names for option bits are defined in the pcre2.h header
+ The following names for option bits are defined in the pcre2.h header
file:
PCRE2_ANCHORED
If this bit is set, the pattern is forced to be "anchored", that is, it
- is constrained to match only at the first matching point in the string
- that is being searched (the "subject string"). This effect can also be
- achieved by appropriate constructs in the pattern itself, which is the
+ is constrained to match only at the first matching point in the string
+ that is being searched (the "subject string"). This effect can also be
+ achieved by appropriate constructs in the pattern itself, which is the
only way to do it in Perl.
PCRE2_ALLOW_EMPTY_CLASS
- By default, for compatibility with Perl, a closing square bracket that
- immediately follows an opening one is treated as a data character for
- the class. When PCRE2_ALLOW_EMPTY_CLASS is set, it terminates the
+ By default, for compatibility with Perl, a closing square bracket that
+ immediately follows an opening one is treated as a data character for
+ the class. When PCRE2_ALLOW_EMPTY_CLASS is set, it terminates the
class, which therefore contains no characters and so can never match.
PCRE2_ALT_BSUX
- This option request alternative handling of three escape sequences,
- which makes PCRE2's behaviour more like ECMAscript (aka JavaScript).
+ This option request alternative handling of three escape sequences,
+ which makes PCRE2's behaviour more like ECMAscript (aka JavaScript).
When it is set:
(1) \U matches an upper case "U" character; by default \U causes a com-
@@ -1410,244 +1440,244 @@
pile time error (Perl uses \U to upper case subsequent characters).
(2) \u matches a lower case "u" character unless it is followed by four
- hexadecimal digits, in which case the hexadecimal number defines the
- code point to match. By default, \u causes a compile time error (Perl
+ hexadecimal digits, in which case the hexadecimal number defines the
+ code point to match. By default, \u causes a compile time error (Perl
uses it to upper case the following character).
- (3) \x matches a lower case "x" character unless it is followed by two
- hexadecimal digits, in which case the hexadecimal number defines the
- code point to match. By default, as in Perl, a hexadecimal number is
+ (3) \x matches a lower case "x" character unless it is followed by two
+ hexadecimal digits, in which case the hexadecimal number defines the
+ code point to match. By default, as in Perl, a hexadecimal number is
always expected after \x, but it may have zero, one, or two digits (so,
for example, \xz matches a binary zero character followed by z).
ECMAscript 6 added additional functionality to \u. This can be accessed
- using the PCRE2_EXTRA_ALT_BSUX extra option (see "Extra compile op-
+ using the PCRE2_EXTRA_ALT_BSUX extra option (see "Extra compile op-
tions" below). Note that this alternative escape handling applies only
- to patterns. Neither of these options affects the processing of re-
+ to patterns. Neither of these options affects the processing of re-
placement strings passed to pcre2_substitute().
PCRE2_ALT_CIRCUMFLEX
In multiline mode (when PCRE2_MULTILINE is set), the circumflex
- metacharacter matches at the start of the subject (unless PCRE2_NOTBOL
- is set), and also after any internal newline. However, it does not
+ metacharacter matches at the start of the subject (unless PCRE2_NOTBOL
+ is set), and also after any internal newline. However, it does not
match after a newline at the end of the subject, for compatibility with
- Perl. If you want a multiline circumflex also to match after a termi-
+ Perl. If you want a multiline circumflex also to match after a termi-
nating newline, you must set PCRE2_ALT_CIRCUMFLEX.
PCRE2_ALT_VERBNAMES
- By default, for compatibility with Perl, the name in any verb sequence
- such as (*MARK:NAME) is any sequence of characters that does not in-
- clude a closing parenthesis. The name is not processed in any way, and
- it is not possible to include a closing parenthesis in the name. How-
- ever, if the PCRE2_ALT_VERBNAMES option is set, normal backslash pro-
- cessing is applied to verb names and only an unescaped closing paren-
- thesis terminates the name. A closing parenthesis can be included in a
- name either as \) or between \Q and \E. If the PCRE2_EXTENDED or
- PCRE2_EXTENDED_MORE option is set with PCRE2_ALT_VERBNAMES, unescaped
- whitespace in verb names is skipped and #-comments are recognized, ex-
+ By default, for compatibility with Perl, the name in any verb sequence
+ such as (*MARK:NAME) is any sequence of characters that does not in-
+ clude a closing parenthesis. The name is not processed in any way, and
+ it is not possible to include a closing parenthesis in the name. How-
+ ever, if the PCRE2_ALT_VERBNAMES option is set, normal backslash pro-
+ cessing is applied to verb names and only an unescaped closing paren-
+ thesis terminates the name. A closing parenthesis can be included in a
+ name either as \) or between \Q and \E. If the PCRE2_EXTENDED or
+ PCRE2_EXTENDED_MORE option is set with PCRE2_ALT_VERBNAMES, unescaped
+ whitespace in verb names is skipped and #-comments are recognized, ex-
actly as in the rest of the pattern.
PCRE2_AUTO_CALLOUT
- If this bit is set, pcre2_compile() automatically inserts callout
- items, all with number 255, before each pattern item, except immedi-
- ately before or after an explicit callout in the pattern. For discus-
+ If this bit is set, pcre2_compile() automatically inserts callout
+ items, all with number 255, before each pattern item, except immedi-
+ ately before or after an explicit callout in the pattern. For discus-
sion of the callout facility, see the pcre2callout documentation.
PCRE2_CASELESS
- If this bit is set, letters in the pattern match both upper and lower
- case letters in the subject. It is equivalent to Perl's /i option, and
- it can be changed within a pattern by a (?i) option setting. If either
- PCRE2_UTF or PCRE2_UCP is set, Unicode properties are used for all
- characters with more than one other case, and for all characters whose
- code points are greater than U+007F. Note that there are two ASCII
+ If this bit is set, letters in the pattern match both upper and lower
+ case letters in the subject. It is equivalent to Perl's /i option, and
+ it can be changed within a pattern by a (?i) option setting. If either
+ PCRE2_UTF or PCRE2_UCP is set, Unicode properties are used for all
+ characters with more than one other case, and for all characters whose
+ code points are greater than U+007F. Note that there are two ASCII
characters, K and S, that, in addition to their lower case ASCII equiv-
- alents, are case-equivalent with U+212A (Kelvin sign) and U+017F (long
- S) respectively. For lower valued characters with only one other case,
- a lookup table is used for speed. When neither PCRE2_UTF nor PCRE2_UCP
- is set, a lookup table is used for all code points less than 256, and
- higher code points (available only in 16-bit or 32-bit mode) are
+ alents, are case-equivalent with U+212A (Kelvin sign) and U+017F (long
+ S) respectively. For lower valued characters with only one other case,
+ a lookup table is used for speed. When neither PCRE2_UTF nor PCRE2_UCP
+ is set, a lookup table is used for all code points less than 256, and
+ higher code points (available only in 16-bit or 32-bit mode) are
treated as not having another case.
PCRE2_DOLLAR_ENDONLY
- If this bit is set, a dollar metacharacter in the pattern matches only
- at the end of the subject string. Without this option, a dollar also
- matches immediately before a newline at the end of the string (but not
- before any other newlines). The PCRE2_DOLLAR_ENDONLY option is ignored
- if PCRE2_MULTILINE is set. There is no equivalent to this option in
+ If this bit is set, a dollar metacharacter in the pattern matches only
+ at the end of the subject string. Without this option, a dollar also
+ matches immediately before a newline at the end of the string (but not
+ before any other newlines). The PCRE2_DOLLAR_ENDONLY option is ignored
+ if PCRE2_MULTILINE is set. There is no equivalent to this option in
Perl, and no way to set it within a pattern.
PCRE2_DOTALL
- If this bit is set, a dot metacharacter in the pattern matches any
- character, including one that indicates a newline. However, it only
+ If this bit is set, a dot metacharacter in the pattern matches any
+ character, including one that indicates a newline. However, it only
ever matches one character, even if newlines are coded as CRLF. Without
this option, a dot does not match when the current position in the sub-
- ject is at a newline. This option is equivalent to Perl's /s option,
+ ject is at a newline. This option is equivalent to Perl's /s option,
and it can be changed within a pattern by a (?s) option setting. A neg-
- ative class such as [^a] always matches newline characters, and the \N
- escape sequence always matches a non-newline character, independent of
+ ative class such as [^a] always matches newline characters, and the \N
+ escape sequence always matches a non-newline character, independent of
the setting of PCRE2_DOTALL.
PCRE2_DUPNAMES
- If this bit is set, names used to identify capture groups need not be
- unique. This can be helpful for certain types of pattern when it is
- known that only one instance of the named group can ever be matched.
- There are more details of named capture groups below; see also the
+ If this bit is set, names used to identify capture groups need not be
+ unique. This can be helpful for certain types of pattern when it is
+ known that only one instance of the named group can ever be matched.
+ There are more details of named capture groups below; see also the
pcre2pattern documentation.
PCRE2_ENDANCHORED
- If this bit is set, the end of any pattern match must be right at the
+ If this bit is set, the end of any pattern match must be right at the
end of the string being searched (the "subject string"). If the pattern
match succeeds by reaching (*ACCEPT), but does not reach the end of the
- subject, the match fails at the current starting point. For unanchored
- patterns, a new match is then tried at the next starting point. How-
+ subject, the match fails at the current starting point. For unanchored
+ patterns, a new match is then tried at the next starting point. How-
ever, if the match succeeds by reaching the end of the pattern, but not
- the end of the subject, backtracking occurs and an alternative match
+ the end of the subject, backtracking occurs and an alternative match
may be found. Consider these two patterns:
.(*ACCEPT)|..
.|..
- If matched against "abc" with PCRE2_ENDANCHORED set, the first matches
- "c" whereas the second matches "bc". The effect of PCRE2_ENDANCHORED
- can also be achieved by appropriate constructs in the pattern itself,
+ If matched against "abc" with PCRE2_ENDANCHORED set, the first matches
+ "c" whereas the second matches "bc". The effect of PCRE2_ENDANCHORED
+ can also be achieved by appropriate constructs in the pattern itself,
which is the only way to do it in Perl.
For DFA matching with pcre2_dfa_match(), PCRE2_ENDANCHORED applies only
- to the first (that is, the longest) matched string. Other parallel
- matches, which are necessarily substrings of the first one, must obvi-
+ to the first (that is, the longest) matched string. Other parallel
+ matches, which are necessarily substrings of the first one, must obvi-
ously end before the end of the subject.
PCRE2_EXTENDED
- If this bit is set, most white space characters in the pattern are to-
+ If this bit is set, most white space characters in the pattern are to-
tally ignored except when escaped or inside a character class. However,
- white space is not allowed within sequences such as (?> that introduce
- various parenthesized groups, nor within numerical quantifiers such as
+ white space is not allowed within sequences such as (?> that introduce
+ various parenthesized groups, nor within numerical quantifiers such as
{1,3}. Ignorable white space is permitted between an item and a follow-
- ing quantifier and between a quantifier and a following + that indi-
+ ing quantifier and between a quantifier and a following + that indi-
cates possessiveness. PCRE2_EXTENDED is equivalent to Perl's /x option,
and it can be changed within a pattern by a (?x) option setting.
- When PCRE2 is compiled without Unicode support, PCRE2_EXTENDED recog-
- nizes as white space only those characters with code points less than
+ When PCRE2 is compiled without Unicode support, PCRE2_EXTENDED recog-
+ nizes as white space only those characters with code points less than
256 that are flagged as white space in its low-character table. The ta-
ble is normally created by pcre2_maketables(), which uses the isspace()
- function to identify space characters. In most ASCII environments, the
- relevant characters are those with code points 0x0009 (tab), 0x000A
- (linefeed), 0x000B (vertical tab), 0x000C (formfeed), 0x000D (carriage
+ function to identify space characters. In most ASCII environments, the
+ relevant characters are those with code points 0x0009 (tab), 0x000A
+ (linefeed), 0x000B (vertical tab), 0x000C (formfeed), 0x000D (carriage
return), and 0x0020 (space).
When PCRE2 is compiled with Unicode support, in addition to these char-
- acters, five more Unicode "Pattern White Space" characters are recog-
+ acters, five more Unicode "Pattern White Space" characters are recog-
nized by PCRE2_EXTENDED. These are U+0085 (next line), U+200E (left-to-
- right mark), U+200F (right-to-left mark), U+2028 (line separator), and
- U+2029 (paragraph separator). This set of characters is the same as
- recognized by Perl's /x option. Note that the horizontal and vertical
- space characters that are matched by the \h and \v escapes in patterns
+ right mark), U+200F (right-to-left mark), U+2028 (line separator), and
+ U+2029 (paragraph separator). This set of characters is the same as
+ recognized by Perl's /x option. Note that the horizontal and vertical
+ space characters that are matched by the \h and \v escapes in patterns
are a much bigger set.
- As well as ignoring most white space, PCRE2_EXTENDED also causes char-
- acters between an unescaped # outside a character class and the next
- newline, inclusive, to be ignored, which makes it possible to include
+ As well as ignoring most white space, PCRE2_EXTENDED also causes char-
+ acters between an unescaped # outside a character class and the next
+ newline, inclusive, to be ignored, which makes it possible to include
comments inside complicated patterns. Note that the end of this type of
- comment is a literal newline sequence in the pattern; escape sequences
+ comment is a literal newline sequence in the pattern; escape sequences
that happen to represent a newline do not count.
Which characters are interpreted as newlines can be specified by a set-
- ting in the compile context that is passed to pcre2_compile() or by a
- special sequence at the start of the pattern, as described in the sec-
- tion entitled "Newline conventions" in the pcre2pattern documentation.
+ ting in the compile context that is passed to pcre2_compile() or by a
+ special sequence at the start of the pattern, as described in the sec-
+ tion entitled "Newline conventions" in the pcre2pattern documentation.
A default is defined when PCRE2 is built.
PCRE2_EXTENDED_MORE
- This option has the effect of PCRE2_EXTENDED, but, in addition, un-
- escaped space and horizontal tab characters are ignored inside a char-
- acter class. Note: only these two characters are ignored, not the full
- set of pattern white space characters that are ignored outside a char-
- acter class. PCRE2_EXTENDED_MORE is equivalent to Perl's /xx option,
+ This option has the effect of PCRE2_EXTENDED, but, in addition, un-
+ escaped space and horizontal tab characters are ignored inside a char-
+ acter class. Note: only these two characters are ignored, not the full
+ set of pattern white space characters that are ignored outside a char-
+ acter class. PCRE2_EXTENDED_MORE is equivalent to Perl's /xx option,
and it can be changed within a pattern by a (?xx) option setting.
PCRE2_FIRSTLINE
If this option is set, the start of an unanchored pattern match must be
- before or at the first newline in the subject string following the
- start of matching, though the matched text may continue over the new-
+ before or at the first newline in the subject string following the
+ start of matching, though the matched text may continue over the new-
line. If startoffset is non-zero, the limiting newline is not necessar-
- ily the first newline in the subject. For example, if the subject
+ ily the first newline in the subject. For example, if the subject
string is "abc\nxyz" (where \n represents a single-character newline) a
- pattern match for "yz" succeeds with PCRE2_FIRSTLINE if startoffset is
- greater than 3. See also PCRE2_USE_OFFSET_LIMIT, which provides a more
- general limiting facility. If PCRE2_FIRSTLINE is set with an offset
- limit, a match must occur in the first line and also within the offset
+ pattern match for "yz" succeeds with PCRE2_FIRSTLINE if startoffset is
+ greater than 3. See also PCRE2_USE_OFFSET_LIMIT, which provides a more
+ general limiting facility. If PCRE2_FIRSTLINE is set with an offset
+ limit, a match must occur in the first line and also within the offset
limit. In other words, whichever limit comes first is used.
PCRE2_LITERAL
If this option is set, all meta-characters in the pattern are disabled,
- and it is treated as a literal string. Matching literal strings with a
+ and it is treated as a literal string. Matching literal strings with a
regular expression engine is not the most efficient way of doing it. If
- you are doing a lot of literal matching and are worried about effi-
+ you are doing a lot of literal matching and are worried about effi-
ciency, you should consider using other approaches. The only other main
options that are allowed with PCRE2_LITERAL are: PCRE2_ANCHORED,
PCRE2_ENDANCHORED, PCRE2_AUTO_CALLOUT, PCRE2_CASELESS, PCRE2_FIRSTLINE,
PCRE2_MATCH_INVALID_UTF, PCRE2_NO_START_OPTIMIZE, PCRE2_NO_UTF_CHECK,
- PCRE2_UTF, and PCRE2_USE_OFFSET_LIMIT. The extra options PCRE2_EX-
+ PCRE2_UTF, and PCRE2_USE_OFFSET_LIMIT. The extra options PCRE2_EX-
TRA_MATCH_LINE and PCRE2_EXTRA_MATCH_WORD are also supported. Any other
options cause an error.
PCRE2_MATCH_INVALID_UTF
- This option forces PCRE2_UTF (see below) and also enables support for
- matching by pcre2_match() in subject strings that contain invalid UTF
- sequences. This facility is not supported for DFA matching. For de-
+ This option forces PCRE2_UTF (see below) and also enables support for
+ matching by pcre2_match() in subject strings that contain invalid UTF
+ sequences. This facility is not supported for DFA matching. For de-
tails, see the pcre2unicode documentation.
PCRE2_MATCH_UNSET_BACKREF
- If this option is set, a backreference to an unset capture group
- matches an empty string (by default this causes the current matching
+ If this option is set, a backreference to an unset capture group
+ matches an empty string (by default this causes the current matching
alternative to fail). A pattern such as (\1)(a) succeeds when this op-
- tion is set (assuming it can find an "a" in the subject), whereas it
- fails by default, for Perl compatibility. Setting this option makes
+ tion is set (assuming it can find an "a" in the subject), whereas it
+ fails by default, for Perl compatibility. Setting this option makes
PCRE2 behave more like ECMAscript (aka JavaScript).
PCRE2_MULTILINE
- By default, for the purposes of matching "start of line" and "end of
- line", PCRE2 treats the subject string as consisting of a single line
- of characters, even if it actually contains newlines. The "start of
- line" metacharacter (^) matches only at the start of the string, and
- the "end of line" metacharacter ($) matches only at the end of the
- string, or before a terminating newline (except when PCRE2_DOLLAR_EN-
+ By default, for the purposes of matching "start of line" and "end of
+ line", PCRE2 treats the subject string as consisting of a single line
+ of characters, even if it actually contains newlines. The "start of
+ line" metacharacter (^) matches only at the start of the string, and
+ the "end of line" metacharacter ($) matches only at the end of the
+ string, or before a terminating newline (except when PCRE2_DOLLAR_EN-
DONLY is set). Note, however, that unless PCRE2_DOTALL is set, the "any
- character" metacharacter (.) does not match at a newline. This behav-
+ character" metacharacter (.) does not match at a newline. This behav-
iour (for ^, $, and dot) is the same as Perl.
- When PCRE2_MULTILINE it is set, the "start of line" and "end of line"
- constructs match immediately following or immediately before internal
- newlines in the subject string, respectively, as well as at the very
- start and end. This is equivalent to Perl's /m option, and it can be
+ When PCRE2_MULTILINE it is set, the "start of line" and "end of line"
+ constructs match immediately following or immediately before internal
+ newlines in the subject string, respectively, as well as at the very
+ start and end. This is equivalent to Perl's /m option, and it can be
changed within a pattern by a (?m) option setting. Note that the "start
of line" metacharacter does not match after a newline at the end of the
- subject, for compatibility with Perl. However, you can change this by
- setting the PCRE2_ALT_CIRCUMFLEX option. If there are no newlines in a
- subject string, or no occurrences of ^ or $ in a pattern, setting
+ subject, for compatibility with Perl. However, you can change this by
+ setting the PCRE2_ALT_CIRCUMFLEX option. If there are no newlines in a
+ subject string, or no occurrences of ^ or $ in a pattern, setting
PCRE2_MULTILINE has no effect.
PCRE2_NEVER_BACKSLASH_C
- This option locks out the use of \C in the pattern that is being com-
- piled. This escape can cause unpredictable behaviour in UTF-8 or
- UTF-16 modes, because it may leave the current matching point in the
+ This option locks out the use of \C in the pattern that is being com-
+ piled. This escape can cause unpredictable behaviour in UTF-8 or
+ UTF-16 modes, because it may leave the current matching point in the
middle of a multi-code-unit character. This option may be useful in ap-
plications that process patterns from external sources. Note that there
is also a build-time option that permanently locks out the use of \C.
@@ -1654,20 +1684,20 @@
PCRE2_NEVER_UCP
- This option locks out the use of Unicode properties for handling \B,
+ This option locks out the use of Unicode properties for handling \B,
\b, \D, \d, \S, \s, \W, \w, and some of the POSIX character classes, as
- described for the PCRE2_UCP option below. In particular, it prevents
- the creator of the pattern from enabling this facility by starting the
- pattern with (*UCP). This option may be useful in applications that
+ described for the PCRE2_UCP option below. In particular, it prevents
+ the creator of the pattern from enabling this facility by starting the
+ pattern with (*UCP). This option may be useful in applications that
process patterns from external sources. The option combination PCRE_UCP
and PCRE_NEVER_UCP causes an error.
PCRE2_NEVER_UTF
- This option locks out interpretation of the pattern as UTF-8, UTF-16,
+ This option locks out interpretation of the pattern as UTF-8, UTF-16,
or UTF-32, depending on which library is in use. In particular, it pre-
- vents the creator of the pattern from switching to UTF interpretation
- by starting the pattern with (*UTF). This option may be useful in ap-
+ vents the creator of the pattern from switching to UTF interpretation
+ by starting the pattern with (*UTF). This option may be useful in ap-
plications that process patterns from external sources. The combination
of PCRE2_UTF and PCRE2_NEVER_UTF causes an error.
@@ -1674,122 +1704,122 @@
PCRE2_NO_AUTO_CAPTURE
If this option is set, it disables the use of numbered capturing paren-
- theses in the pattern. Any opening parenthesis that is not followed by
- ? behaves as if it were followed by ?: but named parentheses can still
+ theses in the pattern. Any opening parenthesis that is not followed by
+ ? behaves as if it were followed by ?: but named parentheses can still
be used for capturing (and they acquire numbers in the usual way). This
- is the same as Perl's /n option. Note that, when this option is set,
- references to capture groups (backreferences or recursion/subroutine
- calls) may only refer to named groups, though the reference can be by
+ is the same as Perl's /n option. Note that, when this option is set,
+ references to capture groups (backreferences or recursion/subroutine
+ calls) may only refer to named groups, though the reference can be by
name or by number.
PCRE2_NO_AUTO_POSSESS
If this option is set, it disables "auto-possessification", which is an
- optimization that, for example, turns a+b into a++b in order to avoid
- backtracks into a+ that can never be successful. However, if callouts
- are in use, auto-possessification means that some callouts are never
+ optimization that, for example, turns a+b into a++b in order to avoid
+ backtracks into a+ that can never be successful. However, if callouts
+ are in use, auto-possessification means that some callouts are never
taken. You can set this option if you want the matching functions to do
- a full unoptimized search and run all the callouts, but it is mainly
+ a full unoptimized search and run all the callouts, but it is mainly
provided for testing purposes.
PCRE2_NO_DOTSTAR_ANCHOR
If this option is set, it disables an optimization that is applied when
- .* is the first significant item in a top-level branch of a pattern,
- and all the other branches also start with .* or with \A or \G or ^.
- The optimization is automatically disabled for .* if it is inside an
+ .* is the first significant item in a top-level branch of a pattern,
+ and all the other branches also start with .* or with \A or \G or ^.
+ The optimization is automatically disabled for .* if it is inside an
atomic group or a capture group that is the subject of a backreference,
- or if the pattern contains (*PRUNE) or (*SKIP). When the optimization
- is not disabled, such a pattern is automatically anchored if
+ or if the pattern contains (*PRUNE) or (*SKIP). When the optimization
+ is not disabled, such a pattern is automatically anchored if
PCRE2_DOTALL is set for all the .* items and PCRE2_MULTILINE is not set
- for any ^ items. Otherwise, the fact that any match must start either
- at the start of the subject or following a newline is remembered. Like
+ for any ^ items. Otherwise, the fact that any match must start either
+ at the start of the subject or following a newline is remembered. Like
other optimizations, this can cause callouts to be skipped.
PCRE2_NO_START_OPTIMIZE
- This is an option whose main effect is at matching time. It does not
+ This is an option whose main effect is at matching time. It does not
change what pcre2_compile() generates, but it does affect the output of
the JIT compiler.
- There are a number of optimizations that may occur at the start of a
- match, in order to speed up the process. For example, if it is known
- that an unanchored match must start with a specific code unit value,
- the matching code searches the subject for that value, and fails imme-
- diately if it cannot find it, without actually running the main match-
- ing function. This means that a special item such as (*COMMIT) at the
- start of a pattern is not considered until after a suitable starting
- point for the match has been found. Also, when callouts or (*MARK)
- items are in use, these "start-up" optimizations can cause them to be
- skipped if the pattern is never actually used. The start-up optimiza-
- tions are in effect a pre-scan of the subject that takes place before
+ There are a number of optimizations that may occur at the start of a
+ match, in order to speed up the process. For example, if it is known
+ that an unanchored match must start with a specific code unit value,
+ the matching code searches the subject for that value, and fails imme-
+ diately if it cannot find it, without actually running the main match-
+ ing function. This means that a special item such as (*COMMIT) at the
+ start of a pattern is not considered until after a suitable starting
+ point for the match has been found. Also, when callouts or (*MARK)
+ items are in use, these "start-up" optimizations can cause them to be
+ skipped if the pattern is never actually used. The start-up optimiza-
+ tions are in effect a pre-scan of the subject that takes place before
the pattern is run.
The PCRE2_NO_START_OPTIMIZE option disables the start-up optimizations,
- possibly causing performance to suffer, but ensuring that in cases
- where the result is "no match", the callouts do occur, and that items
+ possibly causing performance to suffer, but ensuring that in cases
+ where the result is "no match", the callouts do occur, and that items
such as (*COMMIT) and (*MARK) are considered at every possible starting
position in the subject string.
- Setting PCRE2_NO_START_OPTIMIZE may change the outcome of a matching
+ Setting PCRE2_NO_START_OPTIMIZE may change the outcome of a matching
operation. Consider the pattern
(*COMMIT)ABC
- When this is compiled, PCRE2 records the fact that a match must start
- with the character "A". Suppose the subject string is "DEFABC". The
- start-up optimization scans along the subject, finds "A" and runs the
- first match attempt from there. The (*COMMIT) item means that the pat-
- tern must match the current starting position, which in this case, it
- does. However, if the same match is run with PCRE2_NO_START_OPTIMIZE
- set, the initial scan along the subject string does not happen. The
- first match attempt is run starting from "D" and when this fails,
- (*COMMIT) prevents any further matches being tried, so the overall re-
+ When this is compiled, PCRE2 records the fact that a match must start
+ with the character "A". Suppose the subject string is "DEFABC". The
+ start-up optimization scans along the subject, finds "A" and runs the
+ first match attempt from there. The (*COMMIT) item means that the pat-
+ tern must match the current starting position, which in this case, it
+ does. However, if the same match is run with PCRE2_NO_START_OPTIMIZE
+ set, the initial scan along the subject string does not happen. The
+ first match attempt is run starting from "D" and when this fails,
+ (*COMMIT) prevents any further matches being tried, so the overall re-
sult is "no match".
- As another start-up optimization makes use of a minimum length for a
+ As another start-up optimization makes use of a minimum length for a
matching subject, which is recorded when possible. Consider the pattern
(*MARK:1)B(*MARK:2)(X|Y)
- The minimum length for a match is two characters. If the subject is
+ The minimum length for a match is two characters. If the subject is
"XXBB", the "starting character" optimization skips "XX", then tries to
- match "BB", which is long enough. In the process, (*MARK:2) is encoun-
- tered and remembered. When the match attempt fails, the next "B" is
- found, but there is only one character left, so there are no more at-
- tempts, and "no match" is returned with the "last mark seen" set to
- "2". If NO_START_OPTIMIZE is set, however, matches are tried at every
- possible starting position, including at the end of the subject, where
- (*MARK:1) is encountered, but there is no "B", so the "last mark seen"
- that is returned is "1". In this case, the optimizations do not affect
+ match "BB", which is long enough. In the process, (*MARK:2) is encoun-
+ tered and remembered. When the match attempt fails, the next "B" is
+ found, but there is only one character left, so there are no more at-
+ tempts, and "no match" is returned with the "last mark seen" set to
+ "2". If NO_START_OPTIMIZE is set, however, matches are tried at every
+ possible starting position, including at the end of the subject, where
+ (*MARK:1) is encountered, but there is no "B", so the "last mark seen"
+ that is returned is "1". In this case, the optimizations do not affect
the overall match result, which is still "no match", but they do affect
the auxiliary information that is returned.
PCRE2_NO_UTF_CHECK
- When PCRE2_UTF is set, the validity of the pattern as a UTF string is
- automatically checked. There are discussions about the validity of
- UTF-8 strings, UTF-16 strings, and UTF-32 strings in the pcre2unicode
- document. If an invalid UTF sequence is found, pcre2_compile() returns
+ When PCRE2_UTF is set, the validity of the pattern as a UTF string is
+ automatically checked. There are discussions about the validity of
+ UTF-8 strings, UTF-16 strings, and UTF-32 strings in the pcre2unicode
+ document. If an invalid UTF sequence is found, pcre2_compile() returns
a negative error code.
- If you know that your pattern is a valid UTF string, and you want to
- skip this check for performance reasons, you can set the
+ If you know that your pattern is a valid UTF string, and you want to
+ skip this check for performance reasons, you can set the
PCRE2_NO_UTF_CHECK option. When it is set, the effect of passing an in-
- valid UTF string as a pattern is undefined. It may cause your program
+ valid UTF string as a pattern is undefined. It may cause your program
to crash or loop.
Note that this option can also be passed to pcre2_match() and
- pcre_dfa_match(), to suppress UTF validity checking of the subject
+ pcre_dfa_match(), to suppress UTF validity checking of the subject
string.
Note also that setting PCRE2_NO_UTF_CHECK at compile time does not dis-
- able the error that is given if an escape sequence for an invalid Uni-
- code code point is encountered in the pattern. In particular, the so-
- called "surrogate" code points (0xd800 to 0xdfff) are invalid. If you
- want to allow escape sequences such as \x{d800} you can set the
- PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES extra option, as described in the
- section entitled "Extra compile options" below. However, this is pos-
+ able the error that is given if an escape sequence for an invalid Uni-
+ code code point is encountered in the pattern. In particular, the so-
+ called "surrogate" code points (0xd800 to 0xdfff) are invalid. If you
+ want to allow escape sequences such as \x{d800} you can set the
+ PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES extra option, as described in the
+ section entitled "Extra compile options" below. However, this is pos-
sible only in UTF-8 and UTF-32 modes, because these values are not rep-
resentable in UTF-16.
@@ -1796,132 +1826,132 @@
PCRE2_UCP
This option has two effects. Firstly, it change the way PCRE2 processes
- \B, \b, \D, \d, \S, \s, \W, \w, and some of the POSIX character
- classes. By default, only ASCII characters are recognized, but if
+ \B, \b, \D, \d, \S, \s, \W, \w, and some of the POSIX character
+ classes. By default, only ASCII characters are recognized, but if
PCRE2_UCP is set, Unicode properties are used instead to classify char-
- acters. More details are given in the section on generic character
- types in the pcre2pattern page. If you set PCRE2_UCP, matching one of
+ acters. More details are given in the section on generic character
+ types in the pcre2pattern page. If you set PCRE2_UCP, matching one of
the items it affects takes much longer.
- The second effect of PCRE2_UCP is to force the use of Unicode proper-
- ties for upper/lower casing operations on characters with code points
- greater than 127, even when PCRE2_UTF is not set. This makes it possi-
+ The second effect of PCRE2_UCP is to force the use of Unicode proper-
+ ties for upper/lower casing operations on characters with code points
+ greater than 127, even when PCRE2_UTF is not set. This makes it possi-
ble, for example, to process strings in the 16-bit UCS-2 code. This op-
- tion is available only if PCRE2 has been compiled with Unicode support
+ tion is available only if PCRE2 has been compiled with Unicode support
(which is the default).
PCRE2_UNGREEDY
- This option inverts the "greediness" of the quantifiers so that they
- are not greedy by default, but become greedy if followed by "?". It is
- not compatible with Perl. It can also be set by a (?U) option setting
+ This option inverts the "greediness" of the quantifiers so that they
+ are not greedy by default, but become greedy if followed by "?". It is
+ not compatible with Perl. It can also be set by a (?U) option setting
within the pattern.
PCRE2_USE_OFFSET_LIMIT
This option must be set for pcre2_compile() if pcre2_set_offset_limit()
- is going to be used to set a non-default offset limit in a match con-
- text for matches that use this pattern. An error is generated if an
- offset limit is set without this option. For more details, see the de-
- scription of pcre2_set_offset_limit() in the section that describes
+ is going to be used to set a non-default offset limit in a match con-
+ text for matches that use this pattern. An error is generated if an
+ offset limit is set without this option. For more details, see the de-
+ scription of pcre2_set_offset_limit() in the section that describes
match contexts. See also the PCRE2_FIRSTLINE option above.
PCRE2_UTF
- This option causes PCRE2 to regard both the pattern and the subject
- strings that are subsequently processed as strings of UTF characters
- instead of single-code-unit strings. It is available when PCRE2 is
- built to include Unicode support (which is the default). If Unicode
+ This option causes PCRE2 to regard both the pattern and the subject
+ strings that are subsequently processed as strings of UTF characters
+ instead of single-code-unit strings. It is available when PCRE2 is
+ built to include Unicode support (which is the default). If Unicode
support is not available, the use of this option provokes an error. De-
- tails of how PCRE2_UTF changes the behaviour of PCRE2 are given in the
+ tails of how PCRE2_UTF changes the behaviour of PCRE2 are given in the
pcre2unicode page. In particular, note that it changes the way
PCRE2_CASELESS handles characters with code points greater than 127.
Extra compile options
- The option bits that can be set in a compile context by calling the
+ The option bits that can be set in a compile context by calling the
pcre2_set_compile_extra_options() function are as follows:
PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES
- This option applies when compiling a pattern in UTF-8 or UTF-32 mode.
- It is forbidden in UTF-16 mode, and ignored in non-UTF modes. Unicode
+ This option applies when compiling a pattern in UTF-8 or UTF-32 mode.
+ It is forbidden in UTF-16 mode, and ignored in non-UTF modes. Unicode
"surrogate" code points in the range 0xd800 to 0xdfff are used in pairs
- in UTF-16 to encode code points with values in the range 0x10000 to
- 0x10ffff. The surrogates cannot therefore be represented in UTF-16.
+ in UTF-16 to encode code points with values in the range 0x10000 to
+ 0x10ffff. The surrogates cannot therefore be represented in UTF-16.
They can be represented in UTF-8 and UTF-32, but are defined as invalid
- code points, and cause errors if encountered in a UTF-8 or UTF-32
+ code points, and cause errors if encountered in a UTF-8 or UTF-32
string that is being checked for validity by PCRE2.
- These values also cause errors if encountered in escape sequences such
+ These values also cause errors if encountered in escape sequences such
as \x{d912} within a pattern. However, it seems that some applications,
when using PCRE2 to check for unwanted characters in UTF-8 strings, ex-
- plicitly test for the surrogates using escape sequences. The
- PCRE2_NO_UTF_CHECK option does not disable the error that occurs, be-
+ plicitly test for the surrogates using escape sequences. The
+ PCRE2_NO_UTF_CHECK option does not disable the error that occurs, be-
cause it applies only to the testing of input strings for UTF validity.
- If the extra option PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES is set, surro-
- gate code point values in UTF-8 and UTF-32 patterns no longer provoke
- errors and are incorporated in the compiled pattern. However, they can
- only match subject characters if the matching function is called with
+ If the extra option PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES is set, surro-
+ gate code point values in UTF-8 and UTF-32 patterns no longer provoke
+ errors and are incorporated in the compiled pattern. However, they can
+ only match subject characters if the matching function is called with
PCRE2_NO_UTF_CHECK set.
PCRE2_EXTRA_ALT_BSUX
- The original option PCRE2_ALT_BSUX causes PCRE2 to process \U, \u, and
- \x in the way that ECMAscript (aka JavaScript) does. Additional func-
+ The original option PCRE2_ALT_BSUX causes PCRE2 to process \U, \u, and
+ \x in the way that ECMAscript (aka JavaScript) does. Additional func-
tionality was defined by ECMAscript 6; setting PCRE2_EXTRA_ALT_BSUX has
- the effect of PCRE2_ALT_BSUX, but in addition it recognizes \u{hhh..}
+ the effect of PCRE2_ALT_BSUX, but in addition it recognizes \u{hhh..}
as a hexadecimal character code, where hhh.. is any number of hexadeci-
mal digits.
PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL
- This is a dangerous option. Use with care. By default, an unrecognized
- escape such as \j or a malformed one such as \x{2z} causes a compile-
+ This is a dangerous option. Use with care. By default, an unrecognized
+ escape such as \j or a malformed one such as \x{2z} causes a compile-
time error when detected by pcre2_compile(). Perl is somewhat inconsis-
- tent in handling such items: for example, \j is treated as a literal
- "j", and non-hexadecimal digits in \x{} are just ignored, though warn-
- ings are given in both cases if Perl's warning switch is enabled. How-
- ever, a malformed octal number after \o{ always causes an error in
+ tent in handling such items: for example, \j is treated as a literal
+ "j", and non-hexadecimal digits in \x{} are just ignored, though warn-
+ ings are given in both cases if Perl's warning switch is enabled. How-
+ ever, a malformed octal number after \o{ always causes an error in
Perl.
- If the PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL extra option is passed to
- pcre2_compile(), all unrecognized or malformed escape sequences are
- treated as single-character escapes. For example, \j is a literal "j"
- and \x{2z} is treated as the literal string "x{2z}". Setting this op-
+ If the PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL extra option is passed to
+ pcre2_compile(), all unrecognized or malformed escape sequences are
+ treated as single-character escapes. For example, \j is a literal "j"
+ and \x{2z} is treated as the literal string "x{2z}". Setting this op-
tion means that typos in patterns may go undetected and have unexpected
- results. Also note that a sequence such as [\N{] is interpreted as a
- malformed attempt at [\N{...}] and so is treated as [N{] whereas [\N]
+ results. Also note that a sequence such as [\N{] is interpreted as a
+ malformed attempt at [\N{...}] and so is treated as [N{] whereas [\N]
gives an error because an unqualified \N is a valid escape sequence but
- is not supported in a character class. To reiterate: this is a danger-
+ is not supported in a character class. To reiterate: this is a danger-
ous option. Use with great care.
PCRE2_EXTRA_ESCAPED_CR_IS_LF
- There are some legacy applications where the escape sequence \r in a
- pattern is expected to match a newline. If this option is set, \r in a
- pattern is converted to \n so that it matches a LF (linefeed) instead
- of a CR (carriage return) character. The option does not affect a lit-
- eral CR in the pattern, nor does it affect CR specified as an explicit
+ There are some legacy applications where the escape sequence \r in a
+ pattern is expected to match a newline. If this option is set, \r in a
+ pattern is converted to \n so that it matches a LF (linefeed) instead
+ of a CR (carriage return) character. The option does not affect a lit-
+ eral CR in the pattern, nor does it affect CR specified as an explicit
code point such as \x{0D}.
PCRE2_EXTRA_MATCH_LINE
- This option is provided for use by the -x option of pcre2grep. It
- causes the pattern only to match complete lines. This is achieved by
- automatically inserting the code for "^(?:" at the start of the com-
- piled pattern and ")$" at the end. Thus, when PCRE2_MULTILINE is set,
- the matched line may be in the middle of the subject string. This op-
+ This option is provided for use by the -x option of pcre2grep. It
+ causes the pattern only to match complete lines. This is achieved by
+ automatically inserting the code for "^(?:" at the start of the com-
+ piled pattern and ")$" at the end. Thus, when PCRE2_MULTILINE is set,
+ the matched line may be in the middle of the subject string. This op-
tion can be used with PCRE2_LITERAL.
PCRE2_EXTRA_MATCH_WORD
- This option is provided for use by the -w option of pcre2grep. It
- causes the pattern only to match strings that have a word boundary at
- the start and the end. This is achieved by automatically inserting the
- code for "\b(?:" at the start of the compiled pattern and ")\b" at the
- end. The option may be used with PCRE2_LITERAL. However, it is ignored
+ This option is provided for use by the -w option of pcre2grep. It
+ causes the pattern only to match strings that have a word boundary at
+ the start and the end. This is achieved by automatically inserting the
+ code for "\b(?:" at the start of the compiled pattern and ")\b" at the
+ end. The option may be used with PCRE2_LITERAL. However, it is ignored
if PCRE2_EXTRA_MATCH_LINE is also set.
@@ -1944,16 +1974,16 @@
void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);
- These functions provide support for JIT compilation, which, if the
- just-in-time compiler is available, further processes a compiled pat-
+ These functions provide support for JIT compilation, which, if the
+ just-in-time compiler is available, further processes a compiled pat-
tern into machine code that executes much faster than the pcre2_match()
- interpretive matching function. Full details are given in the pcre2jit
+ interpretive matching function. Full details are given in the pcre2jit
documentation.
- JIT compilation is a heavyweight optimization. It can take some time
- for patterns to be analyzed, and for one-off matches and simple pat-
- terns the benefit of faster execution might be offset by a much slower
- compilation time. Most (but not all) patterns can be optimized by the
+ JIT compilation is a heavyweight optimization. It can take some time
+ for patterns to be analyzed, and for one-off matches and simple pat-
+ terns the benefit of faster execution might be offset by a much slower
+ compilation time. Most (but not all) patterns can be optimized by the
JIT compiler.
@@ -1964,46 +1994,46 @@
void pcre2_maketables_free(pcre2_general_context *gcontext,
const uint8_t *tables);
- PCRE2 handles caseless matching, and determines whether characters are
- letters, digits, or whatever, by reference to a set of tables, indexed
+ PCRE2 handles caseless matching, and determines whether characters are
+ letters, digits, or whatever, by reference to a set of tables, indexed
by character code point. However, this applies only to characters whose
- code points are less than 256. By default, higher-valued code points
+ code points are less than 256. By default, higher-valued code points
never match escapes such as \w or \d.
- When PCRE2 is built with Unicode support (the default), the Unicode
+ When PCRE2 is built with Unicode support (the default), the Unicode
properties of all characters can be tested with \p and \P, or, alterna-
- tively, the PCRE2_UCP option can be set when a pattern is compiled;
- this causes \w and friends to use Unicode property support instead of
- the built-in tables. PCRE2_UCP also causes upper/lower casing opera-
- tions on characters with code points greater than 127 to use Unicode
+ tively, the PCRE2_UCP option can be set when a pattern is compiled;
+ this causes \w and friends to use Unicode property support instead of
+ the built-in tables. PCRE2_UCP also causes upper/lower casing opera-
+ tions on characters with code points greater than 127 to use Unicode
properties. These effects apply even when PCRE2_UTF is not set.
- The use of locales with Unicode is discouraged. If you are handling
- characters with code points greater than 127, you should either use
+ The use of locales with Unicode is discouraged. If you are handling
+ characters with code points greater than 127, you should either use
Unicode support, or use locales, but not try to mix the two.
- PCRE2 contains a built-in set of character tables that are used by de-
- fault. These are sufficient for many applications. Normally, the in-
- ternal tables recognize only ASCII characters. However, when PCRE2 is
+ PCRE2 contains a built-in set of character tables that are used by de-
+ fault. These are sufficient for many applications. Normally, the in-
+ ternal tables recognize only ASCII characters. However, when PCRE2 is
built, it is possible to cause the internal tables to be rebuilt in the
default "C" locale of the local system, which may cause them to be dif-
ferent.
- The built-in tables can be overridden by tables supplied by the appli-
- cation that calls PCRE2. These may be created in a different locale
- from the default. As more and more applications change to using Uni-
+ The built-in tables can be overridden by tables supplied by the appli-
+ cation that calls PCRE2. These may be created in a different locale
+ from the default. As more and more applications change to using Uni-
code, the need for this locale support is expected to die away.
- External tables are built by calling the pcre2_maketables() function,
+ External tables are built by calling the pcre2_maketables() function,
in the relevant locale. The only argument to this function is a general
- context, which can be used to pass a custom memory allocator. If the
+ context, which can be used to pass a custom memory allocator. If the
argument is NULL, the system malloc() is used. The result can be passed
to pcre2_compile() as often as necessary, by creating a compile context
- and calling pcre2_set_character_tables() to set the tables pointer
+ and calling pcre2_set_character_tables() to set the tables pointer
therein.
- For example, to build and use tables that are appropriate for the
- French locale (where accented characters with values greater than 127
+ For example, to build and use tables that are appropriate for the
+ French locale (where accented characters with values greater than 127
are treated as letters), the following code could be used:
setlocale(LC_CTYPE, "fr_FR");
@@ -2012,31 +2042,31 @@
pcre2_set_character_tables(ccontext, tables);
re = pcre2_compile(..., ccontext);
- The locale name "fr_FR" is used on Linux and other Unix-like systems;
+ The locale name "fr_FR" is used on Linux and other Unix-like systems;
if you are using Windows, the name for the French locale is "french".
The pointer that is passed (via the compile context) to pcre2_compile()
is saved with the compiled pattern, and the same tables are used by the
- matching functions. Thus, for any single pattern, compilation and
- matching both happen in the same locale, but different patterns can be
+ matching functions. Thus, for any single pattern, compilation and
+ matching both happen in the same locale, but different patterns can be
processed in different locales.
- It is the caller's responsibility to ensure that the memory containing
+ It is the caller's responsibility to ensure that the memory containing
the tables remains available while they are still in use. When they are
- no longer needed, you can discard them using pcre2_maketables_free(),
- which should pass as its first parameter the same global context that
+ no longer needed, you can discard them using pcre2_maketables_free(),
+ which should pass as its first parameter the same global context that
was used to create the tables.
Saving locale tables
- The tables described above are just a sequence of binary bytes, which
- makes them independent of hardware characteristics such as endianness
- or whether the processor is 32-bit or 64-bit. A copy of the result of
- pcre2_maketables() can therefore be saved in a file or elsewhere and
- re-used later, even in a different program or on another computer. The
- size of the tables (number of bytes) must be obtained by calling
- pcre2_config() with the PCRE2_CONFIG_TABLES_LENGTH option because
- pcre2_maketables() does not return this value. Note that the
+ The tables described above are just a sequence of binary bytes, which
+ makes them independent of hardware characteristics such as endianness
+ or whether the processor is 32-bit or 64-bit. A copy of the result of
+ pcre2_maketables() can therefore be saved in a file or elsewhere and
+ re-used later, even in a different program or on another computer. The
+ size of the tables (number of bytes) must be obtained by calling
+ pcre2_config() with the PCRE2_CONFIG_TABLES_LENGTH option because
+ pcre2_maketables() does not return this value. Note that the
pcre2_dftables program, which is part of the PCRE2 build system, can be
used stand-alone to create a file that contains a set of binary tables.
See the pcre2build documentation for details.
@@ -2046,13 +2076,13 @@
int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where);
- The pcre2_pattern_info() function returns general information about a
+ The pcre2_pattern_info() function returns general information about a
compiled pattern. For information about callouts, see the next section.
- The first argument for pcre2_pattern_info() is a pointer to the com-
+ The first argument for pcre2_pattern_info() is a pointer to the com-
piled pattern. The second argument specifies which piece of information
- is required, and the third argument is a pointer to a variable to re-
- ceive the data. If the third argument is NULL, the first argument is
- ignored, and the function returns the size in bytes of the variable
+ is required, and the third argument is a pointer to a variable to re-
+ ceive the data. If the third argument is NULL, the first argument is
+ ignored, and the function returns the size in bytes of the variable
that is required for the information requested. Otherwise, the yield of
the function is zero for success, or one of the following negative num-
bers:
@@ -2063,8 +2093,8 @@
PCRE2_ERROR_UNSET the requested field is not set
The "magic number" is placed at the start of each compiled pattern as a
- simple check against passing an arbitrary memory pointer. Here is a
- typical call of pcre2_pattern_info(), to obtain the length of the com-
+ simple check against passing an arbitrary memory pointer. Here is a
+ typical call of pcre2_pattern_info(), to obtain the length of the com-
piled pattern:
int rc;
@@ -2082,22 +2112,22 @@
PCRE2_INFO_EXTRAOPTIONS
Return copies of the pattern's options. The third argument should point
- to a uint32_t variable. PCRE2_INFO_ARGOPTIONS returns exactly the op-
- tions that were passed to pcre2_compile(), whereas PCRE2_INFO_ALLOP-
- TIONS returns the compile options as modified by any top-level (*XXX)
- option settings such as (*UTF) at the start of the pattern itself.
- PCRE2_INFO_EXTRAOPTIONS returns the extra options that were set in the
- compile context by calling the pcre2_set_compile_extra_options() func-
+ to a uint32_t variable. PCRE2_INFO_ARGOPTIONS returns exactly the op-
+ tions that were passed to pcre2_compile(), whereas PCRE2_INFO_ALLOP-
+ TIONS returns the compile options as modified by any top-level (*XXX)
+ option settings such as (*UTF) at the start of the pattern itself.
+ PCRE2_INFO_EXTRAOPTIONS returns the extra options that were set in the
+ compile context by calling the pcre2_set_compile_extra_options() func-
tion.
- For example, if the pattern /(*UTF)abc/ is compiled with the PCRE2_EX-
- TENDED option, the result for PCRE2_INFO_ALLOPTIONS is PCRE2_EXTENDED
- and PCRE2_UTF. Option settings such as (?i) that can change within a
+ For example, if the pattern /(*UTF)abc/ is compiled with the PCRE2_EX-
+ TENDED option, the result for PCRE2_INFO_ALLOPTIONS is PCRE2_EXTENDED
+ and PCRE2_UTF. Option settings such as (?i) that can change within a
pattern do not affect the result of PCRE2_INFO_ALLOPTIONS, even if they
- appear right at the start of the pattern. (This was different in some
+ appear right at the start of the pattern. (This was different in some
earlier releases.)
- A pattern compiled without PCRE2_ANCHORED is automatically anchored by
+ A pattern compiled without PCRE2_ANCHORED is automatically anchored by
PCRE2 if the first significant item in every top-level branch is one of
the following:
@@ -2106,7 +2136,7 @@
\G always
.* sometimes - see below
- When .* is the first significant item, anchoring is possible only when
+ When .* is the first significant item, anchoring is possible only when
all the following are true:
.* is not in an atomic group
@@ -2116,15 +2146,15 @@
Neither (*PRUNE) nor (*SKIP) appears in the pattern
PCRE2_NO_DOTSTAR_ANCHOR is not set
- For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set in
+ For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set in
the options returned for PCRE2_INFO_ALLOPTIONS.
PCRE2_INFO_BACKREFMAX
- Return the number of the highest backreference in the pattern. The
- third argument should point to a uint32_t variable. Named capture
- groups acquire numbers as well as names, and these count towards the
- highest backreference. Backreferences such as \4 or \g{12} match the
+ Return the number of the highest backreference in the pattern. The
+ third argument should point to a uint32_t variable. Named capture
+ groups acquire numbers as well as names, and these count towards the
+ highest backreference. Backreferences such as \4 or \g{12} match the
captured characters of the given group, but in addition, the check that
a capture group is set in a conditional group such as (?(3)a|b) is also
a backreference. Zero is returned if there are no backreferences.
@@ -2131,56 +2161,56 @@
PCRE2_INFO_BSR
- The output is a uint32_t integer whose value indicates what character
- sequences the \R escape sequence matches. A value of PCRE2_BSR_UNICODE
- means that \R matches any Unicode line ending sequence; a value of
+ The output is a uint32_t integer whose value indicates what character
+ sequences the \R escape sequence matches. A value of PCRE2_BSR_UNICODE
+ means that \R matches any Unicode line ending sequence; a value of
PCRE2_BSR_ANYCRLF means that \R matches only CR, LF, or CRLF.
PCRE2_INFO_CAPTURECOUNT
- Return the highest capture group number in the pattern. In patterns
+ Return the highest capture group number in the pattern. In patterns
where (?| is not used, this is also the total number of capture groups.
The third argument should point to a uint32_t variable.
PCRE2_INFO_DEPTHLIMIT
- If the pattern set a backtracking depth limit by including an item of
- the form (*LIMIT_DEPTH=nnnn) at the start, the value is returned. The
+ If the pattern set a backtracking depth limit by including an item of
+ the form (*LIMIT_DEPTH=nnnn) at the start, the value is returned. The
third argument should point to a uint32_t integer. If no such value has
- been set, the call to pcre2_pattern_info() returns the error PCRE2_ER-
+ been set, the call to pcre2_pattern_info() returns the error PCRE2_ER-
ROR_UNSET. Note that this limit will only be used during matching if it
- is less than the limit set or defaulted by the caller of the match
+ is less than the limit set or defaulted by the caller of the match
function.
PCRE2_INFO_FIRSTBITMAP
- In the absence of a single first code unit for a non-anchored pattern,
- pcre2_compile() may construct a 256-bit table that defines a fixed set
- of values for the first code unit in any match. For example, a pattern
- that starts with [abc] results in a table with three bits set. When
- code unit values greater than 255 are supported, the flag bit for 255
- means "any code unit of value 255 or above". If such a table was con-
- structed, a pointer to it is returned. Otherwise NULL is returned. The
+ In the absence of a single first code unit for a non-anchored pattern,
+ pcre2_compile() may construct a 256-bit table that defines a fixed set
+ of values for the first code unit in any match. For example, a pattern
+ that starts with [abc] results in a table with three bits set. When
+ code unit values greater than 255 are supported, the flag bit for 255
+ means "any code unit of value 255 or above". If such a table was con-
+ structed, a pointer to it is returned. Otherwise NULL is returned. The
third argument should point to a const uint8_t * variable.
PCRE2_INFO_FIRSTCODETYPE
Return information about the first code unit of any matched string, for
- a non-anchored pattern. The third argument should point to a uint32_t
- variable. If there is a fixed first value, for example, the letter "c"
- from a pattern such as (cat|cow|coyote), 1 is returned, and the value
- can be retrieved using PCRE2_INFO_FIRSTCODEUNIT. If there is no fixed
- first value, but it is known that a match can occur only at the start
- of the subject or following a newline in the subject, 2 is returned.
+ a non-anchored pattern. The third argument should point to a uint32_t
+ variable. If there is a fixed first value, for example, the letter "c"
+ from a pattern such as (cat|cow|coyote), 1 is returned, and the value
+ can be retrieved using PCRE2_INFO_FIRSTCODEUNIT. If there is no fixed
+ first value, but it is known that a match can occur only at the start
+ of the subject or following a newline in the subject, 2 is returned.
Otherwise, and for anchored patterns, 0 is returned.
PCRE2_INFO_FIRSTCODEUNIT
- Return the value of the first code unit of any matched string for a
- pattern where PCRE2_INFO_FIRSTCODETYPE returns 1; otherwise return 0.
- The third argument should point to a uint32_t variable. In the 8-bit
- library, the value is always less than 256. In the 16-bit library the
- value can be up to 0xffff. In the 32-bit library in UTF-32 mode the
+ Return the value of the first code unit of any matched string for a
+ pattern where PCRE2_INFO_FIRSTCODETYPE returns 1; otherwise return 0.
+ The third argument should point to a uint32_t variable. In the 8-bit
+ library, the value is always less than 256. In the 16-bit library the
+ value can be up to 0xffff. In the 32-bit library in UTF-32 mode the
value can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32
mode.
@@ -2187,8 +2217,8 @@
PCRE2_INFO_FRAMESIZE
Return the size (in bytes) of the data frames that are used to remember
- backtracking positions when the pattern is processed by pcre2_match()
- without the use of JIT. The third argument should point to a size_t
+ backtracking positions when the pattern is processed by pcre2_match()
+ without the use of JIT. The third argument should point to a size_t
variable. The frame size depends on the number of capturing parentheses
in the pattern. Each additional capture group adds two PCRE2_SIZE vari-
ables.
@@ -2195,15 +2225,15 @@
PCRE2_INFO_HASBACKSLASHC
- Return 1 if the pattern contains any instances of \C, otherwise 0. The
+ Return 1 if the pattern contains any instances of \C, otherwise 0. The
third argument should point to a uint32_t variable.
PCRE2_INFO_HASCRORLF
- Return 1 if the pattern contains any explicit matches for CR or LF
- characters, otherwise 0. The third argument should point to a uint32_t
- variable. An explicit match is either a literal CR or LF character, or
- \r or \n or one of the equivalent hexadecimal or octal escape se-
+ Return 1 if the pattern contains any explicit matches for CR or LF
+ characters, otherwise 0. The third argument should point to a uint32_t
+ variable. An explicit match is either a literal CR or LF character, or
+ \r or \n or one of the equivalent hexadecimal or octal escape se-
quences.
PCRE2_INFO_HEAPLIMIT
@@ -2211,45 +2241,45 @@
If the pattern set a heap memory limit by including an item of the form
(*LIMIT_HEAP=nnnn) at the start, the value is returned. The third argu-
ment should point to a uint32_t integer. If no such value has been set,
- the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET.
- Note that this limit will only be used during matching if it is less
+ the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET.
+ Note that this limit will only be used during matching if it is less
than the limit set or defaulted by the caller of the match function.
PCRE2_INFO_JCHANGED
- Return 1 if the (?J) or (?-J) option setting is used in the pattern,
- otherwise 0. The third argument should point to a uint32_t variable.
- (?J) and (?-J) set and unset the local PCRE2_DUPNAMES option, respec-
+ Return 1 if the (?J) or (?-J) option setting is used in the pattern,
+ otherwise 0. The third argument should point to a uint32_t variable.
+ (?J) and (?-J) set and unset the local PCRE2_DUPNAMES option, respec-
tively.
PCRE2_INFO_JITSIZE
- If the compiled pattern was successfully processed by pcre2_jit_com-
- pile(), return the size of the JIT compiled code, otherwise return
+ If the compiled pattern was successfully processed by pcre2_jit_com-
+ pile(), return the size of the JIT compiled code, otherwise return
zero. The third argument should point to a size_t variable.
PCRE2_INFO_LASTCODETYPE
- Returns 1 if there is a rightmost literal code unit that must exist in
- any matched string, other than at its start. The third argument should
+ Returns 1 if there is a rightmost literal code unit that must exist in
+ any matched string, other than at its start. The third argument should
point to a uint32_t variable. If there is no such value, 0 is returned.
- When 1 is returned, the code unit value itself can be retrieved using
+ When 1 is returned, the code unit value itself can be retrieved using
PCRE2_INFO_LASTCODEUNIT. For anchored patterns, a last literal value is
- recorded only if it follows something of variable length. For example,
- for the pattern /^a\d+z\d+/ the returned value is 1 (with "z" returned
- from PCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/ the returned value is
+ recorded only if it follows something of variable length. For example,
+ for the pattern /^a\d+z\d+/ the returned value is 1 (with "z" returned
+ from PCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/ the returned value is
0.
PCRE2_INFO_LASTCODEUNIT
- Return the value of the rightmost literal code unit that must exist in
- any matched string, other than at its start, for a pattern where
+ Return the value of the rightmost literal code unit that must exist in
+ any matched string, other than at its start, for a pattern where
PCRE2_INFO_LASTCODETYPE returns 1. Otherwise, return 0. The third argu-
ment should point to a uint32_t variable.
PCRE2_INFO_MATCHEMPTY
- Return 1 if the pattern might match an empty string, otherwise 0. The
+ Return 1 if the pattern might match an empty string, otherwise 0. The
third argument should point to a uint32_t variable. When a pattern con-
tains recursive subroutine calls it is not always possible to determine
whether or not it can match an empty string. PCRE2 takes a cautious ap-
@@ -2257,44 +2287,44 @@
PCRE2_INFO_MATCHLIMIT
- If the pattern set a match limit by including an item of the form
- (*LIMIT_MATCH=nnnn) at the start, the value is returned. The third ar-
- gument should point to a uint32_t integer. If no such value has been
+ If the pattern set a match limit by including an item of the form
+ (*LIMIT_MATCH=nnnn) at the start, the value is returned. The third ar-
+ gument should point to a uint32_t integer. If no such value has been
set, the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UN-
- SET. Note that this limit will only be used during matching if it is
- less than the limit set or defaulted by the caller of the match func-
+ SET. Note that this limit will only be used during matching if it is
+ less than the limit set or defaulted by the caller of the match func-
tion.
PCRE2_INFO_MAXLOOKBEHIND
- A lookbehind assertion moves back a certain number of characters (not
- code units) when it starts to process each of its branches. This re-
- quest returns the largest of these backward moves. The third argument
+ A lookbehind assertion moves back a certain number of characters (not
+ code units) when it starts to process each of its branches. This re-
+ quest returns the largest of these backward moves. The third argument
should point to a uint32_t integer. The simple assertions \b and \B re-
- quire a one-character lookbehind and cause PCRE2_INFO_MAXLOOKBEHIND to
- return 1 in the absence of anything longer. \A also registers a one-
- character lookbehind, though it does not actually inspect the previous
+ quire a one-character lookbehind and cause PCRE2_INFO_MAXLOOKBEHIND to
+ return 1 in the absence of anything longer. \A also registers a one-
+ character lookbehind, though it does not actually inspect the previous
character.
Note that this information is useful for multi-segment matching only if
- the pattern contains no nested lookbehinds. For example, the pattern
- (?<=a(?<=ba)c) returns a maximum lookbehind of 2, but when it is pro-
- cessed, the first lookbehind moves back by two characters, matches one
- character, then the nested lookbehind also moves back by two charac-
+ the pattern contains no nested lookbehinds. For example, the pattern
+ (?<=a(?<=ba)c) returns a maximum lookbehind of 2, but when it is pro-
+ cessed, the first lookbehind moves back by two characters, matches one
+ character, then the nested lookbehind also moves back by two charac-
ters. This puts the matching point three characters earlier than it was
- at the start. PCRE2_INFO_MAXLOOKBEHIND is really only useful as a de-
- bugging tool. See the pcre2partial documentation for a discussion of
+ at the start. PCRE2_INFO_MAXLOOKBEHIND is really only useful as a de-
+ bugging tool. See the pcre2partial documentation for a discussion of
multi-segment matching.
PCRE2_INFO_MINLENGTH
- If a minimum length for matching subject strings was computed, its
+ If a minimum length for matching subject strings was computed, its
value is returned. Otherwise the returned value is 0. This value is not
- computed when PCRE2_NO_START_OPTIMIZE is set. The value is a number of
- characters, which in UTF mode may be different from the number of code
- units. The third argument should point to a uint32_t variable. The
- value is a lower bound to the length of any matching string. There may
- not be any strings of that length that do actually match, but every
+ computed when PCRE2_NO_START_OPTIMIZE is set. The value is a number of
+ characters, which in UTF mode may be different from the number of code
+ units. The third argument should point to a uint32_t variable. The
+ value is a lower bound to the length of any matching string. There may
+ not be any strings of that length that do actually match, but every
string that does match is at least that long.
PCRE2_INFO_NAMECOUNT
@@ -2302,44 +2332,44 @@
PCRE2_INFO_NAMETABLE
PCRE2 supports the use of named as well as numbered capturing parenthe-
- ses. The names are just an additional way of identifying the parenthe-
+ ses. The names are just an additional way of identifying the parenthe-
ses, which still acquire numbers. Several convenience functions such as
- pcre2_substring_get_byname() are provided for extracting captured sub-
- strings by name. It is also possible to extract the data directly, by
- first converting the name to a number in order to access the correct
- pointers in the output vector (described with pcre2_match() below). To
+ pcre2_substring_get_byname() are provided for extracting captured sub-
+ strings by name. It is also possible to extract the data directly, by
+ first converting the name to a number in order to access the correct
+ pointers in the output vector (described with pcre2_match() below). To
do the conversion, you need to use the name-to-number map, which is de-
scribed by these three values.
- The map consists of a number of fixed-size entries. PCRE2_INFO_NAME-
- COUNT gives the number of entries, and PCRE2_INFO_NAMEENTRYSIZE gives
- the size of each entry in code units; both of these return a uint32_t
+ The map consists of a number of fixed-size entries. PCRE2_INFO_NAME-
+ COUNT gives the number of entries, and PCRE2_INFO_NAMEENTRYSIZE gives
+ the size of each entry in code units; both of these return a uint32_t
value. The entry size depends on the length of the longest name.
PCRE2_INFO_NAMETABLE returns a pointer to the first entry of the table.
This is a PCRE2_SPTR pointer to a block of code units. In the 8-bit li-
- brary, the first two bytes of each entry are the number of the captur-
- ing parenthesis, most significant byte first. In the 16-bit library,
- the pointer points to 16-bit code units, the first of which contains
- the parenthesis number. In the 32-bit library, the pointer points to
- 32-bit code units, the first of which contains the parenthesis number.
+ brary, the first two bytes of each entry are the number of the captur-
+ ing parenthesis, most significant byte first. In the 16-bit library,
+ the pointer points to 16-bit code units, the first of which contains
+ the parenthesis number. In the 32-bit library, the pointer points to
+ 32-bit code units, the first of which contains the parenthesis number.
The rest of the entry is the corresponding name, zero terminated.
- The names are in alphabetical order. If (?| is used to create multiple
+ The names are in alphabetical order. If (?| is used to create multiple
capture groups with the same number, as described in the section on du-
plicate group numbers in the pcre2pattern page, the groups may be given
- the same name, but there is only one entry in the table. Different
+ the same name, but there is only one entry in the table. Different
names for groups of the same number are not permitted.
- Duplicate names for capture groups with different numbers are permit-
+ Duplicate names for capture groups with different numbers are permit-
ted, but only if PCRE2_DUPNAMES is set. They appear in the table in the
- order in which they were found in the pattern. In the absence of (?|
- this is the order of increasing number; when (?| is used this is not
- necessarily the case because later capture groups may have lower num-
+ order in which they were found in the pattern. In the absence of (?|
+ this is the order of increasing number; when (?| is used this is not
+ necessarily the case because later capture groups may have lower num-
bers.
- As a simple example of the name/number table, consider the following
- pattern after compilation by the 8-bit library (assume PCRE2_EXTENDED
+ As a simple example of the name/number table, consider the following
+ pattern after compilation by the 8-bit library (assume PCRE2_EXTENDED
is set, so white space - including newlines - is ignored):
(?<date> (?<year>(\d\d)?\d\d) -
@@ -2346,7 +2376,7 @@
(?<month>\d\d) - (?<day>\d\d) )
There are four named capture groups, so the table has four entries, and
- each entry in the table is eight bytes long. The table is as follows,
+ each entry in the table is eight bytes long. The table is as follows,
with non-printing bytes shows in hexadecimal, and undefined bytes shown
as ??:
@@ -2355,8 +2385,8 @@
00 04 m o n t h 00
00 02 y e a r 00 ??
- When writing code to extract data from named capture groups using the
- name-to-number map, remember that the length of the entries is likely
+ When writing code to extract data from named capture groups using the
+ name-to-number map, remember that the length of the entries is likely
to be different for each compiled pattern.
PCRE2_INFO_NEWLINE
@@ -2375,14 +2405,14 @@
PCRE2_INFO_SIZE
- Return the size of the compiled pattern in bytes (for all three li-
- braries). The third argument should point to a size_t variable. This
- value includes the size of the general data block that precedes the
- code units of the compiled pattern itself. The value that is used when
- pcre2_compile() is getting memory in which to place the compiled pat-
+ Return the size of the compiled pattern in bytes (for all three li-
+ braries). The third argument should point to a size_t variable. This
+ value includes the size of the general data block that precedes the
+ code units of the compiled pattern itself. The value that is used when
+ pcre2_compile() is getting memory in which to place the compiled pat-
tern may be slightly larger than the value returned by this option, be-
- cause there are cases where the code that calculates the size has to
- over-estimate. Processing a pattern with the JIT compiler does not al-
+ cause there are cases where the code that calculates the size has to
+ over-estimate. Processing a pattern with the JIT compiler does not al-
ter the value returned by this option.
@@ -2393,30 +2423,30 @@
void *user_data);
A script language that supports the use of string arguments in callouts
- might like to scan all the callouts in a pattern before running the
+ might like to scan all the callouts in a pattern before running the
match. This can be done by calling pcre2_callout_enumerate(). The first
- argument is a pointer to a compiled pattern, the second points to a
- callback function, and the third is arbitrary user data. The callback
- function is called for every callout in the pattern in the order in
+ argument is a pointer to a compiled pattern, the second points to a
+ callback function, and the third is arbitrary user data. The callback
+ function is called for every callout in the pattern in the order in
which they appear. Its first argument is a pointer to a callout enumer-
- ation block, and its second argument is the user_data value that was
- passed to pcre2_callout_enumerate(). The contents of the callout enu-
- meration block are described in the pcre2callout documentation, which
+ ation block, and its second argument is the user_data value that was
+ passed to pcre2_callout_enumerate(). The contents of the callout enu-
+ meration block are described in the pcre2callout documentation, which
also gives further details about callouts.
SERIALIZATION AND PRECOMPILING
- It is possible to save compiled patterns on disc or elsewhere, and
- reload them later, subject to a number of restrictions. The host on
- which the patterns are reloaded must be running the same version of
+ It is possible to save compiled patterns on disc or elsewhere, and
+ reload them later, subject to a number of restrictions. The host on
+ which the patterns are reloaded must be running the same version of
PCRE2, with the same code unit width, and must also have the same endi-
- anness, pointer width, and PCRE2_SIZE type. Before compiled patterns
- can be saved, they must be converted to a "serialized" form, which in
- the case of PCRE2 is really just a bytecode dump. The functions whose
- names begin with pcre2_serialize_ are used for converting to and from
- the serialized form. They are described in the pcre2serialize documen-
- tation. Note that PCRE2 serialization does not convert compiled pat-
+ anness, pointer width, and PCRE2_SIZE type. Before compiled patterns
+ can be saved, they must be converted to a "serialized" form, which in
+ the case of PCRE2 is really just a bytecode dump. The functions whose
+ names begin with pcre2_serialize_ are used for converting to and from
+ the serialized form. They are described in the pcre2serialize documen-
+ tation. Note that PCRE2 serialization does not convert compiled pat-
terns to an abstract format like Java or .NET serialization.
@@ -2430,58 +2460,58 @@
void pcre2_match_data_free(pcre2_match_data *match_data);
- Information about a successful or unsuccessful match is placed in a
- match data block, which is an opaque structure that is accessed by
- function calls. In particular, the match data block contains a vector
- of offsets into the subject string that define the matched part of the
- subject and any substrings that were captured. This is known as the
+ Information about a successful or unsuccessful match is placed in a
+ match data block, which is an opaque structure that is accessed by
+ function calls. In particular, the match data block contains a vector
+ of offsets into the subject string that define the matched part of the
+ subject and any substrings that were captured. This is known as the
ovector.
- Before calling pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match()
+ Before calling pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match()
you must create a match data block by calling one of the creation func-
- tions above. For pcre2_match_data_create(), the first argument is the
- number of pairs of offsets in the ovector. One pair of offsets is re-
- quired to identify the string that matched the whole pattern, with an
- additional pair for each captured substring. For example, a value of 4
- creates enough space to record the matched portion of the subject plus
- three captured substrings. A minimum of at least 1 pair is imposed by
+ tions above. For pcre2_match_data_create(), the first argument is the
+ number of pairs of offsets in the ovector. One pair of offsets is re-
+ quired to identify the string that matched the whole pattern, with an
+ additional pair for each captured substring. For example, a value of 4
+ creates enough space to record the matched portion of the subject plus
+ three captured substrings. A minimum of at least 1 pair is imposed by
pcre2_match_data_create(), so it is always possible to return the over-
all matched string.
The second argument of pcre2_match_data_create() is a pointer to a gen-
- eral context, which can specify custom memory management for obtaining
+ eral context, which can specify custom memory management for obtaining
the memory for the match data block. If you are not using custom memory
management, pass NULL, which causes malloc() to be used.
- For pcre2_match_data_create_from_pattern(), the first argument is a
+ For pcre2_match_data_create_from_pattern(), the first argument is a
pointer to a compiled pattern. The ovector is created to be exactly the
right size to hold all the substrings a pattern might capture. The sec-
- ond argument is again a pointer to a general context, but in this case
+ ond argument is again a pointer to a general context, but in this case
if NULL is passed, the memory is obtained using the same allocator that
was used for the compiled pattern (custom or default).
- A match data block can be used many times, with the same or different
- compiled patterns. You can extract information from a match data block
- after a match operation has finished, using functions that are de-
+ A match data block can be used many times, with the same or different
+ compiled patterns. You can extract information from a match data block
+ after a match operation has finished, using functions that are de-
scribed in the sections on matched strings and other match data below.
- When a call of pcre2_match() fails, valid data is available in the
- match block only when the error is PCRE2_ERROR_NOMATCH, PCRE2_ER-
- ROR_PARTIAL, or one of the error codes for an invalid UTF string. Ex-
+ When a call of pcre2_match() fails, valid data is available in the
+ match block only when the error is PCRE2_ERROR_NOMATCH, PCRE2_ER-
+ ROR_PARTIAL, or one of the error codes for an invalid UTF string. Ex-
actly what is available depends on the error, and is detailed below.
- When one of the matching functions is called, pointers to the compiled
- pattern and the subject string are set in the match data block so that
- they can be referenced by the extraction functions after a successful
+ When one of the matching functions is called, pointers to the compiled
+ pattern and the subject string are set in the match data block so that
+ they can be referenced by the extraction functions after a successful
match. After running a match, you must not free a compiled pattern or a
- subject string until after all operations on the match data block (for
- that match) have taken place, unless, in the case of the subject
- string, you have used the PCRE2_COPY_MATCHED_SUBJECT option, which is
- described in the section entitled "Option bits for pcre2_match()" be-
+ subject string until after all operations on the match data block (for
+ that match) have taken place, unless, in the case of the subject
+ string, you have used the PCRE2_COPY_MATCHED_SUBJECT option, which is
+ described in the section entitled "Option bits for pcre2_match()" be-
low.
- When a match data block itself is no longer needed, it should be freed
- by calling pcre2_match_data_free(). If this function is called with a
+ When a match data block itself is no longer needed, it should be freed
+ by calling pcre2_match_data_free(). If this function is called with a
NULL argument, it returns immediately, without doing anything.
@@ -2492,15 +2522,15 @@
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
- The function pcre2_match() is called to match a subject string against
- a compiled pattern, which is passed in the code argument. You can call
+ The function pcre2_match() is called to match a subject string against
+ a compiled pattern, which is passed in the code argument. You can call
pcre2_match() with the same code argument as many times as you like, in
- order to find multiple matches in the subject string or to match dif-
+ order to find multiple matches in the subject string or to match dif-
ferent subject strings with the same pattern.
- This function is the main matching facility of the library, and it op-
- erates in a Perl-like manner. For specialist use there is also an al-
- ternative matching function, which is described below in the section
+ This function is the main matching facility of the library, and it op-
+ erates in a Perl-like manner. For specialist use there is also an al-
+ ternative matching function, which is described below in the section
about the pcre2_dfa_match() function.
Here is an example of a simple call to pcre2_match():
@@ -2515,7 +2545,7 @@
md, /* the match data block */
NULL); /* a match context; NULL means use defaults */
- If the subject string is zero-terminated, the length can be given as
+ If the subject string is zero-terminated, the length can be given as
PCRE2_ZERO_TERMINATED. A match context must be provided if certain less
common matching parameters are to be changed. For details, see the sec-
tion on the match context above.
@@ -2522,110 +2552,110 @@
The string to be matched by pcre2_match()
- The subject string is passed to pcre2_match() as a pointer in subject,
- a length in length, and a starting offset in startoffset. The length
- and offset are in code units, not characters. That is, they are in
- bytes for the 8-bit library, 16-bit code units for the 16-bit library,
- and 32-bit code units for the 32-bit library, whether or not UTF pro-
+ The subject string is passed to pcre2_match() as a pointer in subject,
+ a length in length, and a starting offset in startoffset. The length
+ and offset are in code units, not characters. That is, they are in
+ bytes for the 8-bit library, 16-bit code units for the 16-bit library,
+ and 32-bit code units for the 32-bit library, whether or not UTF pro-
cessing is enabled.
If startoffset is greater than the length of the subject, pcre2_match()
- returns PCRE2_ERROR_BADOFFSET. When the starting offset is zero, the
- search for a match starts at the beginning of the subject, and this is
+ returns PCRE2_ERROR_BADOFFSET. When the starting offset is zero, the
+ search for a match starts at the beginning of the subject, and this is
by far the most common case. In UTF-8 or UTF-16 mode, the starting off-
- set must point to the start of a character, or to the end of the sub-
- ject (in UTF-32 mode, one code unit equals one character, so all off-
- sets are valid). Like the pattern string, the subject may contain bi-
+ set must point to the start of a character, or to the end of the sub-
+ ject (in UTF-32 mode, one code unit equals one character, so all off-
+ sets are valid). Like the pattern string, the subject may contain bi-
nary zeros.
- A non-zero starting offset is useful when searching for another match
- in the same subject by calling pcre2_match() again after a previous
- success. Setting startoffset differs from passing over a shortened
- string and setting PCRE2_NOTBOL in the case of a pattern that begins
+ A non-zero starting offset is useful when searching for another match
+ in the same subject by calling pcre2_match() again after a previous
+ success. Setting startoffset differs from passing over a shortened
+ string and setting PCRE2_NOTBOL in the case of a pattern that begins
with any kind of lookbehind. For example, consider the pattern
\Biss\B
- which finds occurrences of "iss" in the middle of words. (\B matches
- only if the current position in the subject is not a word boundary.)
+ which finds occurrences of "iss" in the middle of words. (\B matches
+ only if the current position in the subject is not a word boundary.)
When applied to the string "Mississipi" the first call to pcre2_match()
- finds the first occurrence. If pcre2_match() is called again with just
- the remainder of the subject, namely "issipi", it does not match, be-
- cause \B is always false at the start of the subject, which is deemed
- to be a word boundary. However, if pcre2_match() is passed the entire
+ finds the first occurrence. If pcre2_match() is called again with just
+ the remainder of the subject, namely "issipi", it does not match, be-
+ cause \B is always false at the start of the subject, which is deemed
+ to be a word boundary. However, if pcre2_match() is passed the entire
string again, but with startoffset set to 4, it finds the second occur-
- rence of "iss" because it is able to look behind the starting point to
+ rence of "iss" because it is able to look behind the starting point to
discover that it is preceded by a letter.
- Finding all the matches in a subject is tricky when the pattern can
+ Finding all the matches in a subject is tricky when the pattern can
match an empty string. It is possible to emulate Perl's /g behaviour by
- first trying the match again at the same offset, with the
- PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED options, and then if that
- fails, advancing the starting offset and trying an ordinary match
- again. There is some code that demonstrates how to do this in the
- pcre2demo sample program. In the most general case, you have to check
- to see if the newline convention recognizes CRLF as a newline, and if
- so, and the current character is CR followed by LF, advance the start-
+ first trying the match again at the same offset, with the
+ PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED options, and then if that
+ fails, advancing the starting offset and trying an ordinary match
+ again. There is some code that demonstrates how to do this in the
+ pcre2demo sample program. In the most general case, you have to check
+ to see if the newline convention recognizes CRLF as a newline, and if
+ so, and the current character is CR followed by LF, advance the start-
ing offset by two characters instead of one.
If a non-zero starting offset is passed when the pattern is anchored, a
single attempt to match at the given offset is made. This can only suc-
- ceed if the pattern does not require the match to be at the start of
- the subject. In other words, the anchoring must be the result of set-
- ting the PCRE2_ANCHORED option or the use of .* with PCRE2_DOTALL, not
+ ceed if the pattern does not require the match to be at the start of
+ the subject. In other words, the anchoring must be the result of set-
+ ting the PCRE2_ANCHORED option or the use of .* with PCRE2_DOTALL, not
by starting the pattern with ^ or \A.
Option bits for pcre2_match()
The unused bits of the options argument for pcre2_match() must be zero.
- The only bits that may be set are PCRE2_ANCHORED,
- PCRE2_COPY_MATCHED_SUBJECT, PCRE2_ENDANCHORED, PCRE2_NOTBOL, PCRE2_NO-
+ The only bits that may be set are PCRE2_ANCHORED,
+ PCRE2_COPY_MATCHED_SUBJECT, PCRE2_ENDANCHORED, PCRE2_NOTBOL, PCRE2_NO-
TEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_JIT,
- PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT. Their
+ PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT. Their
action is described below.
- Setting PCRE2_ANCHORED or PCRE2_ENDANCHORED at match time is not sup-
- ported by the just-in-time (JIT) compiler. If it is set, JIT matching
- is disabled and the interpretive code in pcre2_match() is run. Apart
- from PCRE2_NO_JIT (obviously), the remaining options are supported for
+ Setting PCRE2_ANCHORED or PCRE2_ENDANCHORED at match time is not sup-
+ ported by the just-in-time (JIT) compiler. If it is set, JIT matching
+ is disabled and the interpretive code in pcre2_match() is run. Apart
+ from PCRE2_NO_JIT (obviously), the remaining options are supported for
JIT matching.
PCRE2_ANCHORED
The PCRE2_ANCHORED option limits pcre2_match() to matching at the first
- matching position. If a pattern was compiled with PCRE2_ANCHORED, or
- turned out to be anchored by virtue of its contents, it cannot be made
- unachored at matching time. Note that setting the option at match time
+ matching position. If a pattern was compiled with PCRE2_ANCHORED, or
+ turned out to be anchored by virtue of its contents, it cannot be made
+ unachored at matching time. Note that setting the option at match time
disables JIT matching.
PCRE2_COPY_MATCHED_SUBJECT
- By default, a pointer to the subject is remembered in the match data
- block so that, after a successful match, it can be referenced by the
- substring extraction functions. This means that the subject's memory
- must not be freed until all such operations are complete. For some ap-
- plications where the lifetime of the subject string is not guaranteed,
- it may be necessary to make a copy of the subject string, but it is
- wasteful to do this unless the match is successful. After a successful
- match, if PCRE2_COPY_MATCHED_SUBJECT is set, the subject is copied and
- the new pointer is remembered in the match data block instead of the
- original subject pointer. The memory allocator that was used for the
- match block itself is used. The copy is automatically freed when
- pcre2_match_data_free() is called to free the match data block. It is
+ By default, a pointer to the subject is remembered in the match data
+ block so that, after a successful match, it can be referenced by the
+ substring extraction functions. This means that the subject's memory
+ must not be freed until all such operations are complete. For some ap-
+ plications where the lifetime of the subject string is not guaranteed,
+ it may be necessary to make a copy of the subject string, but it is
+ wasteful to do this unless the match is successful. After a successful
+ match, if PCRE2_COPY_MATCHED_SUBJECT is set, the subject is copied and
+ the new pointer is remembered in the match data block instead of the
+ original subject pointer. The memory allocator that was used for the
+ match block itself is used. The copy is automatically freed when
+ pcre2_match_data_free() is called to free the match data block. It is
also automatically freed if the match data block is re-used for another
match operation.
PCRE2_ENDANCHORED
- If the PCRE2_ENDANCHORED option is set, any string that pcre2_match()
- matches must be right at the end of the subject string. Note that set-
+ If the PCRE2_ENDANCHORED option is set, any string that pcre2_match()
+ matches must be right at the end of the subject string. Note that set-
ting the option at match time disables JIT matching.
PCRE2_NOTBOL
This option specifies that first character of the subject string is not
- the beginning of a line, so the circumflex metacharacter should not
- match before it. Setting this without having set PCRE2_MULTILINE at
+ the beginning of a line, so the circumflex metacharacter should not
+ match before it. Setting this without having set PCRE2_MULTILINE at
compile time causes circumflex never to match. This option affects only
the behaviour of the circumflex metacharacter. It does not affect \A.
@@ -2632,9 +2662,9 @@
PCRE2_NOTEOL
This option specifies that the end of the subject string is not the end
- of a line, so the dollar metacharacter should not match it nor (except
- in multiline mode) a newline immediately before it. Setting this with-
- out having set PCRE2_MULTILINE at compile time causes dollar never to
+ of a line, so the dollar metacharacter should not match it nor (except
+ in multiline mode) a newline immediately before it. Setting this with-
+ out having set PCRE2_MULTILINE at compile time causes dollar never to
match. This option affects only the behaviour of the dollar metacharac-
ter. It does not affect \Z or \z.
@@ -2641,67 +2671,67 @@
PCRE2_NOTEMPTY
An empty string is not considered to be a valid match if this option is
- set. If there are alternatives in the pattern, they are tried. If all
- the alternatives match the empty string, the entire match fails. For
+ set. If there are alternatives in the pattern, they are tried. If all
+ the alternatives match the empty string, the entire match fails. For
example, if the pattern
a?b?
- is applied to a string not beginning with "a" or "b", it matches an
+ is applied to a string not beginning with "a" or "b", it matches an
empty string at the start of the subject. With PCRE2_NOTEMPTY set, this
- match is not valid, so pcre2_match() searches further into the string
+ match is not valid, so pcre2_match() searches further into the string
for occurrences of "a" or "b".
PCRE2_NOTEMPTY_ATSTART
- This is like PCRE2_NOTEMPTY, except that it locks out an empty string
+ This is like PCRE2_NOTEMPTY, except that it locks out an empty string
match only at the first matching position, that is, at the start of the
- subject plus the starting offset. An empty string match later in the
+ subject plus the starting offset. An empty string match later in the
subject is permitted. If the pattern is anchored, such a match can oc-
cur only if the pattern contains \K.
PCRE2_NO_JIT
- By default, if a pattern has been successfully processed by
- pcre2_jit_compile(), JIT is automatically used when pcre2_match() is
- called with options that JIT supports. Setting PCRE2_NO_JIT disables
+ By default, if a pattern has been successfully processed by
+ pcre2_jit_compile(), JIT is automatically used when pcre2_match() is
+ called with options that JIT supports. Setting PCRE2_NO_JIT disables
the use of JIT; it forces matching to be done by the interpreter.
PCRE2_NO_UTF_CHECK
When PCRE2_UTF is set at compile time, the validity of the subject as a
- UTF string is checked unless PCRE2_NO_UTF_CHECK is passed to
+ UTF string is checked unless PCRE2_NO_UTF_CHECK is passed to
pcre2_match() or PCRE2_MATCH_INVALID_UTF was passed to pcre2_compile().
The latter special case is discussed in detail in the pcre2unicode doc-
umentation.
- In the default case, if a non-zero starting offset is given, the check
- is applied only to that part of the subject that could be inspected
- during matching, and there is a check that the starting offset points
- to the first code unit of a character or to the end of the subject. If
- there are no lookbehind assertions in the pattern, the check starts at
+ In the default case, if a non-zero starting offset is given, the check
+ is applied only to that part of the subject that could be inspected
+ during matching, and there is a check that the starting offset points
+ to the first code unit of a character or to the end of the subject. If
+ there are no lookbehind assertions in the pattern, the check starts at
the starting offset. Otherwise, it starts at the length of the longest
- lookbehind before the starting offset, or at the start of the subject
- if there are not that many characters before the starting offset. Note
+ lookbehind before the starting offset, or at the start of the subject
+ if there are not that many characters before the starting offset. Note
that the sequences \b and \B are one-character lookbehinds.
The check is carried out before any other processing takes place, and a
- negative error code is returned if the check fails. There are several
- UTF error codes for each code unit width, corresponding to different
- problems with the code unit sequence. There are discussions about the
- validity of UTF-8 strings, UTF-16 strings, and UTF-32 strings in the
+ negative error code is returned if the check fails. There are several
+ UTF error codes for each code unit width, corresponding to different
+ problems with the code unit sequence. There are discussions about the
+ validity of UTF-8 strings, UTF-16 strings, and UTF-32 strings in the
pcre2unicode documentation.
If you know that your subject is valid, and you want to skip this check
for performance reasons, you can set the PCRE2_NO_UTF_CHECK option when
- calling pcre2_match(). You might want to do this for the second and
- subsequent calls to pcre2_match() if you are making repeated calls to
+ calling pcre2_match(). You might want to do this for the second and
+ subsequent calls to pcre2_match() if you are making repeated calls to
find multiple matches in the same subject string.
- Warning: Unless PCRE2_MATCH_INVALID_UTF was set at compile time, when
- PCRE2_NO_UTF_CHECK is set at match time the effect of passing an in-
+ Warning: Unless PCRE2_MATCH_INVALID_UTF was set at compile time, when
+ PCRE2_NO_UTF_CHECK is set at match time the effect of passing an in-
valid string as a subject, or an invalid value of startoffset, is unde-
- fined. Your program may crash or loop indefinitely or give wrong re-
+ fined. Your program may crash or loop indefinitely or give wrong re-
sults.
PCRE2_PARTIAL_HARD
@@ -2708,22 +2738,22 @@
PCRE2_PARTIAL_SOFT
These options turn on the partial matching feature. A partial match oc-
- curs if the end of the subject string is reached successfully, but
+ curs if the end of the subject string is reached successfully, but
there are not enough subject characters to complete the match. In addi-
- tion, either at least one character must have been inspected or the
- pattern must contain a lookbehind, or the pattern must be one that
+ tion, either at least one character must have been inspected or the
+ pattern must contain a lookbehind, or the pattern must be one that
could match an empty string.
- If this situation arises when PCRE2_PARTIAL_SOFT (but not PCRE2_PAR-
+ If this situation arises when PCRE2_PARTIAL_SOFT (but not PCRE2_PAR-
TIAL_HARD) is set, matching continues by testing any remaining alterna-
- tives. Only if no complete match can be found is PCRE2_ERROR_PARTIAL
- returned instead of PCRE2_ERROR_NOMATCH. In other words, PCRE2_PAR-
- TIAL_SOFT specifies that the caller is prepared to handle a partial
+ tives. Only if no complete match can be found is PCRE2_ERROR_PARTIAL
+ returned instead of PCRE2_ERROR_NOMATCH. In other words, PCRE2_PAR-
+ TIAL_SOFT specifies that the caller is prepared to handle a partial
match, but only if no complete match can be found.
- If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In this
- case, if a partial match is found, pcre2_match() immediately returns
- PCRE2_ERROR_PARTIAL, without considering any other alternatives. In
+ If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In this
+ case, if a partial match is found, pcre2_match() immediately returns
+ PCRE2_ERROR_PARTIAL, without considering any other alternatives. In
other words, when PCRE2_PARTIAL_HARD is set, a partial match is consid-
ered to be more important that an alternative complete match.
@@ -2733,38 +2763,38 @@
NEWLINE HANDLING WHEN MATCHING
- When PCRE2 is built, a default newline convention is set; this is usu-
- ally the standard convention for the operating system. The default can
- be overridden in a compile context by calling pcre2_set_newline(). It
- can also be overridden by starting a pattern string with, for example,
- (*CRLF), as described in the section on newline conventions in the
- pcre2pattern page. During matching, the newline choice affects the be-
- haviour of the dot, circumflex, and dollar metacharacters. It may also
- alter the way the match starting position is advanced after a match
+ When PCRE2 is built, a default newline convention is set; this is usu-
+ ally the standard convention for the operating system. The default can
+ be overridden in a compile context by calling pcre2_set_newline(). It
+ can also be overridden by starting a pattern string with, for example,
+ (*CRLF), as described in the section on newline conventions in the
+ pcre2pattern page. During matching, the newline choice affects the be-
+ haviour of the dot, circumflex, and dollar metacharacters. It may also
+ alter the way the match starting position is advanced after a match
failure for an unanchored pattern.
When PCRE2_NEWLINE_CRLF, PCRE2_NEWLINE_ANYCRLF, or PCRE2_NEWLINE_ANY is
- set as the newline convention, and a match attempt for an unanchored
+ set as the newline convention, and a match attempt for an unanchored
pattern fails when the current starting position is at a CRLF sequence,
- and the pattern contains no explicit matches for CR or LF characters,
- the match position is advanced by two characters instead of one, in
+ and the pattern contains no explicit matches for CR or LF characters,
+ the match position is advanced by two characters instead of one, in
other words, to after the CRLF.
The above rule is a compromise that makes the most common cases work as
- expected. For example, if the pattern is .+A (and the PCRE2_DOTALL op-
- tion is not set), it does not match the string "\r\nA" because, after
- failing at the start, it skips both the CR and the LF before retrying.
- However, the pattern [\r\n]A does match that string, because it con-
+ expected. For example, if the pattern is .+A (and the PCRE2_DOTALL op-
+ tion is not set), it does not match the string "\r\nA" because, after
+ failing at the start, it skips both the CR and the LF before retrying.
+ However, the pattern [\r\n]A does match that string, because it con-
tains an explicit CR or LF reference, and so advances only by one char-
acter after the first failure.
An explicit match for CR of LF is either a literal appearance of one of
- those characters in the pattern, or one of the \r or \n or equivalent
+ those characters in the pattern, or one of the \r or \n or equivalent
octal or hexadecimal escape sequences. Implicit matches such as [^X] do
- not count, nor does \s, even though it includes CR and LF in the char-
+ not count, nor does \s, even though it includes CR and LF in the char-
acters that it matches.
- Notwithstanding the above, anomalous effects may still occur when CRLF
+ Notwithstanding the above, anomalous effects may still occur when CRLF
is a valid newline sequence and explicit \r or \n escapes appear in the
pattern.
@@ -2775,82 +2805,82 @@
PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);
- In general, a pattern matches a certain portion of the subject, and in
- addition, further substrings from the subject may be picked out by
- parenthesized parts of the pattern. Following the usage in Jeffrey
- Friedl's book, this is called "capturing" in what follows, and the
- phrase "capture group" (Perl terminology) is used for a fragment of a
- pattern that picks out a substring. PCRE2 supports several other kinds
+ In general, a pattern matches a certain portion of the subject, and in
+ addition, further substrings from the subject may be picked out by
+ parenthesized parts of the pattern. Following the usage in Jeffrey
+ Friedl's book, this is called "capturing" in what follows, and the
+ phrase "capture group" (Perl terminology) is used for a fragment of a
+ pattern that picks out a substring. PCRE2 supports several other kinds
of parenthesized group that do not cause substrings to be captured. The
- pcre2_pattern_info() function can be used to find out how many capture
+ pcre2_pattern_info() function can be used to find out how many capture
groups there are in a compiled pattern.
- You can use auxiliary functions for accessing captured substrings by
+ You can use auxiliary functions for accessing captured substrings by
number or by name, as described in sections below.
Alternatively, you can make direct use of the vector of PCRE2_SIZE val-
- ues, called the ovector, which contains the offsets of captured
- strings. It is part of the match data block. The function
- pcre2_get_ovector_pointer() returns the address of the ovector, and
+ ues, called the ovector, which contains the offsets of captured
+ strings. It is part of the match data block. The function
+ pcre2_get_ovector_pointer() returns the address of the ovector, and
pcre2_get_ovector_count() returns the number of pairs of values it con-
tains.
Within the ovector, the first in each pair of values is set to the off-
set of the first code unit of a substring, and the second is set to the
- offset of the first code unit after the end of a substring. These val-
- ues are always code unit offsets, not character offsets. That is, they
+ offset of the first code unit after the end of a substring. These val-
+ ues are always code unit offsets, not character offsets. That is, they
are byte offsets in the 8-bit library, 16-bit offsets in the 16-bit li-
brary, and 32-bit offsets in the 32-bit library.
- After a partial match (error return PCRE2_ERROR_PARTIAL), only the
- first pair of offsets (that is, ovector[0] and ovector[1]) are set.
- They identify the part of the subject that was partially matched. See
+ After a partial match (error return PCRE2_ERROR_PARTIAL), only the
+ first pair of offsets (that is, ovector[0] and ovector[1]) are set.
+ They identify the part of the subject that was partially matched. See
the pcre2partial documentation for details of partial matching.
- After a fully successful match, the first pair of offsets identifies
- the portion of the subject string that was matched by the entire pat-
- tern. The next pair is used for the first captured substring, and so
- on. The value returned by pcre2_match() is one more than the highest
- numbered pair that has been set. For example, if two substrings have
- been captured, the returned value is 3. If there are no captured sub-
+ After a fully successful match, the first pair of offsets identifies
+ the portion of the subject string that was matched by the entire pat-
+ tern. The next pair is used for the first captured substring, and so
+ on. The value returned by pcre2_match() is one more than the highest
+ numbered pair that has been set. For example, if two substrings have
+ been captured, the returned value is 3. If there are no captured sub-
strings, the return value from a successful match is 1, indicating that
just the first pair of offsets has been set.
- If a pattern uses the \K escape sequence within a positive assertion,
+ If a pattern uses the \K escape sequence within a positive assertion,
the reported start of a successful match can be greater than the end of
- the match. For example, if the pattern (?=ab\K) is matched against
+ the match. For example, if the pattern (?=ab\K) is matched against
"ab", the start and end offset values for the match are 2 and 0.
- If a capture group is matched repeatedly within a single match opera-
+ If a capture group is matched repeatedly within a single match opera-
tion, it is the last portion of the subject that it matched that is re-
turned.
If the ovector is too small to hold all the captured substring offsets,
- as much as possible is filled in, and the function returns a value of
- zero. If captured substrings are not of interest, pcre2_match() may be
+ as much as possible is filled in, and the function returns a value of
+ zero. If captured substrings are not of interest, pcre2_match() may be
called with a match data block whose ovector is of minimum length (that
is, one pair).
- It is possible for capture group number n+1 to match some part of the
- subject when group n has not been used at all. For example, if the
+ It is possible for capture group number n+1 to match some part of the
+ subject when group n has not been used at all. For example, if the
string "abc" is matched against the pattern (a|(z))(bc) the return from
- the function is 4, and groups 1 and 3 are matched, but 2 is not. When
- this happens, both values in the offset pairs corresponding to unused
+ the function is 4, and groups 1 and 3 are matched, but 2 is not. When
+ this happens, both values in the offset pairs corresponding to unused
groups are set to PCRE2_UNSET.
- Offset values that correspond to unused groups at the end of the ex-
- pression are also set to PCRE2_UNSET. For example, if the string "abc"
- is matched against the pattern (abc)(x(yz)?)? groups 2 and 3 are not
- matched. The return from the function is 2, because the highest used
- capture group number is 1. The offsets for for the second and third
- capture groupss (assuming the vector is large enough, of course) are
+ Offset values that correspond to unused groups at the end of the ex-
+ pression are also set to PCRE2_UNSET. For example, if the string "abc"
+ is matched against the pattern (abc)(x(yz)?)? groups 2 and 3 are not
+ matched. The return from the function is 2, because the highest used
+ capture group number is 1. The offsets for for the second and third
+ capture groupss (assuming the vector is large enough, of course) are
set to PCRE2_UNSET.
Elements in the ovector that do not correspond to capturing parentheses
in the pattern are never changed. That is, if a pattern contains n cap-
turing parentheses, no more than ovector[0] to ovector[2n+1] are set by
- pcre2_match(). The other elements retain whatever values they previ-
- ously had. After a failed match attempt, the contents of the ovector
+ pcre2_match(). The other elements retain whatever values they previ-
+ ously had. After a failed match attempt, the contents of the ovector
are unchanged.
@@ -2860,25 +2890,25 @@
PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);
- As well as the offsets in the ovector, other information about a match
- is retained in the match data block and can be retrieved by the above
- functions in appropriate circumstances. If they are called at other
+ As well as the offsets in the ovector, other information about a match
+ is retained in the match data block and can be retrieved by the above
+ functions in appropriate circumstances. If they are called at other
times, the result is undefined.
- After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a
- failure to match (PCRE2_ERROR_NOMATCH), a mark name may be available.
- The function pcre2_get_mark() can be called to access this name, which
- can be specified in the pattern by any of the backtracking control
+ After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a
+ failure to match (PCRE2_ERROR_NOMATCH), a mark name may be available.
+ The function pcre2_get_mark() can be called to access this name, which
+ can be specified in the pattern by any of the backtracking control
verbs, not just (*MARK). The same function applies to all the verbs. It
returns a pointer to the zero-terminated name, which is within the com-
piled pattern. If no name is available, NULL is returned. The length of
- the name (excluding the terminating zero) is stored in the code unit
- that precedes the name. You should use this length instead of relying
+ the name (excluding the terminating zero) is stored in the code unit
+ that precedes the name. You should use this length instead of relying
on the terminating zero if the name might contain a binary zero.
- After a successful match, the name that is returned is the last mark
+ After a successful match, the name that is returned is the last mark
name encountered on the matching path through the pattern. Instances of
- backtracking verbs without names do not count. Thus, for example, if
+ backtracking verbs without names do not count. Thus, for example, if
the matching path contains (*MARK:A)(*PRUNE), the name "A" is returned.
After a "no match" or a partial match, the last encountered name is re-
turned. For example, consider this pattern:
@@ -2885,30 +2915,30 @@
^(*MARK:A)((*MARK:B)a|b)c
- When it matches "bc", the returned name is A. The B mark is "seen" in
- the first branch of the group, but it is not on the matching path. On
- the other hand, when this pattern fails to match "bx", the returned
+ When it matches "bc", the returned name is A. The B mark is "seen" in
+ the first branch of the group, but it is not on the matching path. On
+ the other hand, when this pattern fails to match "bx", the returned
name is B.
- Warning: By default, certain start-of-match optimizations are used to
- give a fast "no match" result in some situations. For example, if the
- anchoring is removed from the pattern above, there is an initial check
- for the presence of "c" in the subject before running the matching en-
+ Warning: By default, certain start-of-match optimizations are used to
+ give a fast "no match" result in some situations. For example, if the
+ anchoring is removed from the pattern above, there is an initial check
+ for the presence of "c" in the subject before running the matching en-
gine. This check fails for "bx", causing a match failure without seeing
- any marks. You can disable the start-of-match optimizations by setting
- the PCRE2_NO_START_OPTIMIZE option for pcre2_compile() or by starting
+ any marks. You can disable the start-of-match optimizations by setting
+ the PCRE2_NO_START_OPTIMIZE option for pcre2_compile() or by starting
the pattern with (*NO_START_OPT).
- After a successful match, a partial match, or one of the invalid UTF
- errors (for example, PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar() can
+ After a successful match, a partial match, or one of the invalid UTF
+ errors (for example, PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar() can
be called. After a successful or partial match it returns the code unit
- offset of the character at which the match started. For a non-partial
- match, this can be different to the value of ovector[0] if the pattern
- contains the \K escape sequence. After a partial match, however, this
- value is always the same as ovector[0] because \K does not affect the
+ offset of the character at which the match started. For a non-partial
+ match, this can be different to the value of ovector[0] if the pattern
+ contains the \K escape sequence. After a partial match, however, this
+ value is always the same as ovector[0] because \K does not affect the
result of a partial match.
- After a UTF check failure, pcre2_get_startchar() can be used to obtain
+ After a UTF check failure, pcre2_get_startchar() can be used to obtain
the code unit offset of the invalid UTF character. Details are given in
the pcre2unicode page.
@@ -2915,14 +2945,14 @@
ERROR RETURNS FROM pcre2_match()
- If pcre2_match() fails, it returns a negative number. This can be con-
- verted to a text string by calling the pcre2_get_error_message() func-
- tion (see "Obtaining a textual error message" below). Negative error
- codes are also returned by other functions, and are documented with
- them. The codes are given names in the header file. If UTF checking is
+ If pcre2_match() fails, it returns a negative number. This can be con-
+ verted to a text string by calling the pcre2_get_error_message() func-
+ tion (see "Obtaining a textual error message" below). Negative error
+ codes are also returned by other functions, and are documented with
+ them. The codes are given names in the header file. If UTF checking is
in force and an invalid UTF subject string is detected, one of a number
- of UTF-specific negative error codes is returned. Details are given in
- the pcre2unicode page. The following are the other errors that may be
+ of UTF-specific negative error codes is returned. Details are given in
+ the pcre2unicode page. The following are the other errors that may be
returned by pcre2_match():
PCRE2_ERROR_NOMATCH
@@ -2931,20 +2961,20 @@
PCRE2_ERROR_PARTIAL
- The subject string did not match, but it did match partially. See the
+ The subject string did not match, but it did match partially. See the
pcre2partial documentation for details of partial matching.
PCRE2_ERROR_BADMAGIC
PCRE2 stores a 4-byte "magic number" at the start of the compiled code,
- to catch the case when it is passed a junk pointer. This is the error
+ to catch the case when it is passed a junk pointer. This is the error
that is returned when the magic number is not present.
PCRE2_ERROR_BADMODE
- This error is given when a compiled pattern is passed to a function in
- a library of a different code unit width, for example, a pattern com-
- piled by the 8-bit library is passed to a 16-bit or 32-bit library
+ This error is given when a compiled pattern is passed to a function in
+ a library of a different code unit width, for example, a pattern com-
+ piled by the 8-bit library is passed to a 16-bit or 32-bit library
function.
PCRE2_ERROR_BADOFFSET
@@ -2958,15 +2988,15 @@
PCRE2_ERROR_BADUTFOFFSET
The UTF code unit sequence that was passed as a subject was checked and
- found to be valid (the PCRE2_NO_UTF_CHECK option was not set), but the
- value of startoffset did not point to the beginning of a UTF character
+ found to be valid (the PCRE2_NO_UTF_CHECK option was not set), but the
+ value of startoffset did not point to the beginning of a UTF character
or the end of the subject.
PCRE2_ERROR_CALLOUT
- This error is never generated by pcre2_match() itself. It is provided
- for use by callout functions that want to cause pcre2_match() or
- pcre2_callout_enumerate() to return a distinctive error code. See the
+ This error is never generated by pcre2_match() itself. It is provided
+ for use by callout functions that want to cause pcre2_match() or
+ pcre2_callout_enumerate() to return a distinctive error code. See the
pcre2callout documentation for details.
PCRE2_ERROR_DEPTHLIMIT
@@ -2979,7 +3009,7 @@
PCRE2_ERROR_INTERNAL
- An unexpected internal error has occurred. This error could be caused
+ An unexpected internal error has occurred. This error could be caused
by a bug in PCRE2 or by overwriting of the compiled pattern.
PCRE2_ERROR_JIT_STACKLIMIT
@@ -2986,7 +3016,7 @@
This error is returned when a pattern that was successfully studied us-
ing JIT is being matched, but the memory available for the just-in-time
- processing stack is not large enough. See the pcre2jit documentation
+ processing stack is not large enough. See the pcre2jit documentation
for more details.
PCRE2_ERROR_MATCHLIMIT
@@ -2995,11 +3025,11 @@
PCRE2_ERROR_NOMEMORY
- If a pattern contains many nested backtracking points, heap memory is
- used to remember them. This error is given when the memory allocation
- function (default or custom) fails. Note that a different error,
- PCRE2_ERROR_HEAPLIMIT, is given if the amount of memory needed exceeds
- the heap limit. PCRE2_ERROR_NOMEMORY is also returned if
+ If a pattern contains many nested backtracking points, heap memory is
+ used to remember them. This error is given when the memory allocation
+ function (default or custom) fails. Note that a different error,
+ PCRE2_ERROR_HEAPLIMIT, is given if the amount of memory needed exceeds
+ the heap limit. PCRE2_ERROR_NOMEMORY is also returned if
PCRE2_COPY_MATCHED_SUBJECT is set and memory allocation fails.
PCRE2_ERROR_NULL
@@ -3008,12 +3038,12 @@
PCRE2_ERROR_RECURSELOOP
- This error is returned when pcre2_match() detects a recursion loop
- within the pattern. Specifically, it means that either the whole pat-
+ This error is returned when pcre2_match() detects a recursion loop
+ within the pattern. Specifically, it means that either the whole pat-
tern or a capture group has been called recursively for the second time
- at the same position in the subject string. Some simple patterns that
- might do this are detected and faulted at compile time, but more com-
- plicated cases, in particular mutual recursions between two different
+ at the same position in the subject string. Some simple patterns that
+ might do this are detected and faulted at compile time, but more com-
+ plicated cases, in particular mutual recursions between two different
groups, cannot be detected until matching is attempted.
@@ -3022,20 +3052,20 @@
int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
PCRE2_SIZE bufflen);
- A text message for an error code from any PCRE2 function (compile,
- match, or auxiliary) can be obtained by calling pcre2_get_error_mes-
- sage(). The code is passed as the first argument, with the remaining
- two arguments specifying a code unit buffer and its length in code
- units, into which the text message is placed. The message is returned
- in code units of the appropriate width for the library that is being
+ A text message for an error code from any PCRE2 function (compile,
+ match, or auxiliary) can be obtained by calling pcre2_get_error_mes-
+ sage(). The code is passed as the first argument, with the remaining
+ two arguments specifying a code unit buffer and its length in code
+ units, into which the text message is placed. The message is returned
+ in code units of the appropriate width for the library that is being
used.
- The returned message is terminated with a trailing zero, and the func-
- tion returns the number of code units used, excluding the trailing
+ The returned message is terminated with a trailing zero, and the func-
+ tion returns the number of code units used, excluding the trailing
zero. If the error number is unknown, the negative error code PCRE2_ER-
- ROR_BADDATA is returned. If the buffer is too small, the message is
+ ROR_BADDATA is returned. If the buffer is too small, the message is
truncated (but still with a trailing zero), and the negative error code
- PCRE2_ERROR_NOMEMORY is returned. None of the messages are very long;
+ PCRE2_ERROR_NOMEMORY is returned. None of the messages are very long;
a buffer size of 120 code units is ample.
@@ -3054,39 +3084,39 @@
void pcre2_substring_free(PCRE2_UCHAR *buffer);
- Captured substrings can be accessed directly by using the ovector as
+ Captured substrings can be accessed directly by using the ovector as
described above. For convenience, auxiliary functions are provided for
- extracting captured substrings as new, separate, zero-terminated
+ extracting captured substrings as new, separate, zero-terminated
strings. A substring that contains a binary zero is correctly extracted
- and has a further zero added on the end, but the result is not, of
+ and has a further zero added on the end, but the result is not, of
course, a C string.
The functions in this section identify substrings by number. The number
zero refers to the entire matched substring, with higher numbers refer-
- ring to substrings captured by parenthesized groups. After a partial
- match, only substring zero is available. An attempt to extract any
- other substring gives the error PCRE2_ERROR_PARTIAL. The next section
+ ring to substrings captured by parenthesized groups. After a partial
+ match, only substring zero is available. An attempt to extract any
+ other substring gives the error PCRE2_ERROR_PARTIAL. The next section
describes similar functions for extracting captured substrings by name.
- If a pattern uses the \K escape sequence within a positive assertion,
+ If a pattern uses the \K escape sequence within a positive assertion,
the reported start of a successful match can be greater than the end of
- the match. For example, if the pattern (?=ab\K) is matched against
- "ab", the start and end offset values for the match are 2 and 0. In
- this situation, calling these functions with a zero substring number
+ the match. For example, if the pattern (?=ab\K) is matched against
+ "ab", the start and end offset values for the match are 2 and 0. In
+ this situation, calling these functions with a zero substring number
extracts a zero-length empty string.
- You can find the length in code units of a captured substring without
- extracting it by calling pcre2_substring_length_bynumber(). The first
- argument is a pointer to the match data block, the second is the group
- number, and the third is a pointer to a variable into which the length
- is placed. If you just want to know whether or not the substring has
+ You can find the length in code units of a captured substring without
+ extracting it by calling pcre2_substring_length_bynumber(). The first
+ argument is a pointer to the match data block, the second is the group
+ number, and the third is a pointer to a variable into which the length
+ is placed. If you just want to know whether or not the substring has
been captured, you can pass the third argument as NULL.
- The pcre2_substring_copy_bynumber() function copies a captured sub-
- string into a supplied buffer, whereas pcre2_substring_get_bynumber()
- copies it into new memory, obtained using the same memory allocation
- function that was used for the match data block. The first two argu-
- ments of these functions are a pointer to the match data block and a
+ The pcre2_substring_copy_bynumber() function copies a captured sub-
+ string into a supplied buffer, whereas pcre2_substring_get_bynumber()
+ copies it into new memory, obtained using the same memory allocation
+ function that was used for the match data block. The first two argu-
+ ments of these functions are a pointer to the match data block and a
capture group number.
The final arguments of pcre2_substring_copy_bynumber() are a pointer to
@@ -3095,25 +3125,25 @@
for the extracted substring, excluding the terminating zero.
For pcre2_substring_get_bynumber() the third and fourth arguments point
- to variables that are updated with a pointer to the new memory and the
- number of code units that comprise the substring, again excluding the
- terminating zero. When the substring is no longer needed, the memory
+ to variables that are updated with a pointer to the new memory and the
+ number of code units that comprise the substring, again excluding the
+ terminating zero. When the substring is no longer needed, the memory
should be freed by calling pcre2_substring_free().
- The return value from all these functions is zero for success, or a
- negative error code. If the pattern match failed, the match failure
- code is returned. If a substring number greater than zero is used af-
- ter a partial match, PCRE2_ERROR_PARTIAL is returned. Other possible
+ The return value from all these functions is zero for success, or a
+ negative error code. If the pattern match failed, the match failure
+ code is returned. If a substring number greater than zero is used af-
+ ter a partial match, PCRE2_ERROR_PARTIAL is returned. Other possible
error codes are:
PCRE2_ERROR_NOMEMORY
- The buffer was too small for pcre2_substring_copy_bynumber(), or the
+ The buffer was too small for pcre2_substring_copy_bynumber(), or the
attempt to get memory failed for pcre2_substring_get_bynumber().
PCRE2_ERROR_NOSUBSTRING
- There is no substring with that number in the pattern, that is, the
+ There is no substring with that number in the pattern, that is, the
number is greater than the number of capturing parentheses.
PCRE2_ERROR_UNAVAILABLE
@@ -3124,8 +3154,8 @@
PCRE2_ERROR_UNSET
- The substring did not participate in the match. For example, if the
- pattern is (abc)|(def) and the subject is "def", and the ovector con-
+ The substring did not participate in the match. For example, if the
+ pattern is (abc)|(def) and the subject is "def", and the ovector con-
tains at least two capturing slots, substring number 1 is unset.
@@ -3136,31 +3166,31 @@
void pcre2_substring_list_free(PCRE2_SPTR *list);
- The pcre2_substring_list_get() function extracts all available sub-
- strings and builds a list of pointers to them. It also (optionally)
- builds a second list that contains their lengths (in code units), ex-
- cluding a terminating zero that is added to each of them. All this is
+ The pcre2_substring_list_get() function extracts all available sub-
+ strings and builds a list of pointers to them. It also (optionally)
+ builds a second list that contains their lengths (in code units), ex-
+ cluding a terminating zero that is added to each of them. All this is
done in a single block of memory that is obtained using the same memory
allocation function that was used to get the match data block.
- This function must be called only after a successful match. If called
+ This function must be called only after a successful match. If called
after a partial match, the error code PCRE2_ERROR_PARTIAL is returned.
- The address of the memory block is returned via listptr, which is also
+ The address of the memory block is returned via listptr, which is also
the start of the list of string pointers. The end of the list is marked
- by a NULL pointer. The address of the list of lengths is returned via
- lengthsptr. If your strings do not contain binary zeros and you do not
+ by a NULL pointer. The address of the list of lengths is returned via
+ lengthsptr. If your strings do not contain binary zeros and you do not
therefore need the lengths, you may supply NULL as the lengthsptr argu-
- ment to disable the creation of a list of lengths. The yield of the
- function is zero if all went well, or PCRE2_ERROR_NOMEMORY if the mem-
- ory block could not be obtained. When the list is no longer needed, it
+ ment to disable the creation of a list of lengths. The yield of the
+ function is zero if all went well, or PCRE2_ERROR_NOMEMORY if the mem-
+ ory block could not be obtained. When the list is no longer needed, it
should be freed by calling pcre2_substring_list_free().
If this function encounters a substring that is unset, which can happen
- when capture group number n+1 matches some part of the subject, but
- group n has not been used at all, it returns an empty string. This can
+ when capture group number n+1 matches some part of the subject, but
+ group n has not been used at all, it returns an empty string. This can
be distinguished from a genuine zero-length substring by inspecting the
- appropriate offset in the ovector, which contain PCRE2_UNSET for unset
+ appropriate offset in the ovector, which contain PCRE2_UNSET for unset
substrings, or by calling pcre2_substring_length_bynumber().
@@ -3180,7 +3210,7 @@
void pcre2_substring_free(PCRE2_UCHAR *buffer);
- To extract a substring by name, you first have to find associated num-
+ To extract a substring by name, you first have to find associated num-
ber. For example, for this pattern:
(a+)b(?<xxx>\d+)...
@@ -3188,32 +3218,32 @@
the number of the capture group called "xxx" is 2. If the name is known
to be unique (PCRE2_DUPNAMES was not set), you can find the number from
the name by calling pcre2_substring_number_from_name(). The first argu-
- ment is the compiled pattern, and the second is the name. The yield of
- the function is the group number, PCRE2_ERROR_NOSUBSTRING if there is
- no group with that name, or PCRE2_ERROR_NOUNIQUESUBSTRING if there is
- more than one group with that name. Given the number, you can extract
- the substring directly from the ovector, or use one of the "bynumber"
+ ment is the compiled pattern, and the second is the name. The yield of
+ the function is the group number, PCRE2_ERROR_NOSUBSTRING if there is
+ no group with that name, or PCRE2_ERROR_NOUNIQUESUBSTRING if there is
+ more than one group with that name. Given the number, you can extract
+ the substring directly from the ovector, or use one of the "bynumber"
functions described above.
- For convenience, there are also "byname" functions that correspond to
+ For convenience, there are also "byname" functions that correspond to
the "bynumber" functions, the only difference being that the second ar-
- gument is a name instead of a number. If PCRE2_DUPNAMES is set and
+ gument is a name instead of a number. If PCRE2_DUPNAMES is set and
there are duplicate names, these functions scan all the groups with the
- given name, and return the captured substring from the first named
+ given name, and return the captured substring from the first named
group that is set.
- If there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING is
- returned. If all groups with the name have numbers that are greater
+ If there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING is
+ returned. If all groups with the name have numbers that are greater
than the number of slots in the ovector, PCRE2_ERROR_UNAVAILABLE is re-
- turned. If there is at least one group with a slot in the ovector, but
+ turned. If there is at least one group with a slot in the ovector, but
no group is found to be set, PCRE2_ERROR_UNSET is returned.
Warning: If the pattern uses the (?| feature to set up multiple capture
- groups with the same number, as described in the section on duplicate
+ groups with the same number, as described in the section on duplicate
group numbers in the pcre2pattern page, you cannot use names to distin-
- guish the different capture groups, because names are not included in
- the compiled code. The matching process uses only numbers. For this
- reason, the use of different names for groups with the same number
+ guish the different capture groups, because names are not included in
+ the compiled code. The matching process uses only numbers. For this
+ reason, the use of different names for groups with the same number
causes an error at compile time.
@@ -3226,108 +3256,108 @@
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
PCRE2_SIZE *outlengthptr);
- This function optionally calls pcre2_match() and then makes a copy of
- the subject string in outputbuffer, replacing parts that were matched
- with the replacement string, whose length is supplied in rlength. This
- can be given as PCRE2_ZERO_TERMINATED for a zero-terminated string.
+ This function optionally calls pcre2_match() and then makes a copy of
+ the subject string in outputbuffer, replacing parts that were matched
+ with the replacement string, whose length is supplied in rlength. This
+ can be given as PCRE2_ZERO_TERMINATED for a zero-terminated string.
There is an option (see PCRE2_SUBSTITUTE_REPLACEMENT_ONLY below) to re-
- turn just the replacement string(s). The default action is to perform
- just one replacement if the pattern matches, but there is an option
- that requests multiple replacements (see PCRE2_SUBSTITUTE_GLOBAL be-
+ turn just the replacement string(s). The default action is to perform
+ just one replacement if the pattern matches, but there is an option
+ that requests multiple replacements (see PCRE2_SUBSTITUTE_GLOBAL be-
low).
- If successful, pcre2_substitute() returns the number of substitutions
- that were carried out. This may be zero if no match was found, and is
- never greater than one unless PCRE2_SUBSTITUTE_GLOBAL is set. A nega-
+ If successful, pcre2_substitute() returns the number of substitutions
+ that were carried out. This may be zero if no match was found, and is
+ never greater than one unless PCRE2_SUBSTITUTE_GLOBAL is set. A nega-
tive value is returned if an error is detected.
- Matches in which a \K item in a lookahead in the pattern causes the
- match to end before it starts are not supported, and give rise to an
+ Matches in which a \K item in a lookahead in the pattern causes the
+ match to end before it starts are not supported, and give rise to an
error return. For global replacements, matches in which \K in a lookbe-
- hind causes the match to start earlier than the point that was reached
+ hind causes the match to start earlier than the point that was reached
in the previous iteration are also not supported.
- The first seven arguments of pcre2_substitute() are the same as for
+ The first seven arguments of pcre2_substitute() are the same as for
pcre2_match(), except that the partial matching options are not permit-
- ted, and match_data may be passed as NULL, in which case a match data
- block is obtained and freed within this function, using memory manage-
- ment functions from the match context, if provided, or else those that
+ ted, and match_data may be passed as NULL, in which case a match data
+ block is obtained and freed within this function, using memory manage-
+ ment functions from the match context, if provided, or else those that
were used to allocate memory for the compiled code.
- If match_data is not NULL and PCRE2_SUBSTITUTE_MATCHED is not set, the
+ If match_data is not NULL and PCRE2_SUBSTITUTE_MATCHED is not set, the
provided block is used for all calls to pcre2_match(), and its contents
- afterwards are the result of the final call. For global changes, this
+ afterwards are the result of the final call. For global changes, this
will always be a no-match error. The contents of the ovector within the
match data block may or may not have been changed.
- As well as the usual options for pcre2_match(), a number of additional
- options can be set in the options argument of pcre2_substitute(). One
- such option is PCRE2_SUBSTITUTE_MATCHED. When this is set, an external
- match_data block must be provided, and it must have been used for an
- external call to pcre2_match(). The data in the match_data block (re-
+ As well as the usual options for pcre2_match(), a number of additional
+ options can be set in the options argument of pcre2_substitute(). One
+ such option is PCRE2_SUBSTITUTE_MATCHED. When this is set, an external
+ match_data block must be provided, and it must have been used for an
+ external call to pcre2_match(). The data in the match_data block (re-
turn code, offset vector) is used for the first substitution instead of
- calling pcre2_match() from within pcre2_substitute(). This allows an
+ calling pcre2_match() from within pcre2_substitute(). This allows an
application to check for a match before choosing to substitute, without
having to repeat the match.
- The contents of the externally supplied match data block are not
- changed when PCRE2_SUBSTITUTE_MATCHED is set. If PCRE2_SUBSTI-
- TUTE_GLOBAL is also set, pcre2_match() is called after the first sub-
- stitution to check for further matches, but this is done using an in-
- ternally obtained match data block, thus always leaving the external
+ The contents of the externally supplied match data block are not
+ changed when PCRE2_SUBSTITUTE_MATCHED is set. If PCRE2_SUBSTI-
+ TUTE_GLOBAL is also set, pcre2_match() is called after the first sub-
+ stitution to check for further matches, but this is done using an in-
+ ternally obtained match data block, thus always leaving the external
block unchanged.
- The code argument is not used for matching before the first substitu-
- tion when PCRE2_SUBSTITUTE_MATCHED is set, but it must be provided,
- even when PCRE2_SUBSTITUTE_GLOBAL is not set, because it contains in-
+ The code argument is not used for matching before the first substitu-
+ tion when PCRE2_SUBSTITUTE_MATCHED is set, but it must be provided,
+ even when PCRE2_SUBSTITUTE_GLOBAL is not set, because it contains in-
formation such as the UTF setting and the number of capturing parenthe-
ses in the pattern.
- The default action of pcre2_substitute() is to return a copy of the
+ The default action of pcre2_substitute() is to return a copy of the
subject string with matched substrings replaced. However, if PCRE2_SUB-
- STITUTE_REPLACEMENT_ONLY is set, only the replacement substrings are
+ STITUTE_REPLACEMENT_ONLY is set, only the replacement substrings are
returned. In the global case, multiple replacements are concatenated in
- the output buffer. Substitution callouts (see below) can be used to
+ the output buffer. Substitution callouts (see below) can be used to
separate them if necessary.
- The outlengthptr argument of pcre2_substitute() must point to a vari-
- able that contains the length, in code units, of the output buffer. If
- the function is successful, the value is updated to contain the length
- in code units of the new string, excluding the trailing zero that is
+ The outlengthptr argument of pcre2_substitute() must point to a vari-
+ able that contains the length, in code units, of the output buffer. If
+ the function is successful, the value is updated to contain the length
+ in code units of the new string, excluding the trailing zero that is
automatically added.
- If the function is not successful, the value set via outlengthptr de-
- pends on the type of error. For syntax errors in the replacement
+ If the function is not successful, the value set via outlengthptr de-
+ pends on the type of error. For syntax errors in the replacement
string, the value is the offset in the replacement string where the er-
- ror was detected. For other errors, the value is PCRE2_UNSET by de-
+ ror was detected. For other errors, the value is PCRE2_UNSET by de-
fault. This includes the case of the output buffer being too small, un-
less PCRE2_SUBSTITUTE_OVERFLOW_LENGTH is set.
- PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the output
+ PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the output
buffer is too small. The default action is to return PCRE2_ERROR_NOMEM-
- ORY immediately. If this option is set, however, pcre2_substitute()
+ ORY immediately. If this option is set, however, pcre2_substitute()
continues to go through the motions of matching and substituting (with-
- out, of course, writing anything) in order to compute the size of buf-
- fer that is needed. This value is passed back via the outlengthptr
- variable, with the result of the function still being PCRE2_ER-
+ out, of course, writing anything) in order to compute the size of buf-
+ fer that is needed. This value is passed back via the outlengthptr
+ variable, with the result of the function still being PCRE2_ER-
ROR_NOMEMORY.
- Passing a buffer size of zero is a permitted way of finding out how
- much memory is needed for given substitution. However, this does mean
+ Passing a buffer size of zero is a permitted way of finding out how
+ much memory is needed for given substitution. However, this does mean
that the entire operation is carried out twice. Depending on the appli-
- cation, it may be more efficient to allocate a large buffer and free
- the excess afterwards, instead of using PCRE2_SUBSTITUTE_OVER-
+ cation, it may be more efficient to allocate a large buffer and free
+ the excess afterwards, instead of using PCRE2_SUBSTITUTE_OVER-
FLOW_LENGTH.
- The replacement string, which is interpreted as a UTF string in UTF
- mode, is checked for UTF validity unless PCRE2_NO_UTF_CHECK is set. An
+ The replacement string, which is interpreted as a UTF string in UTF
+ mode, is checked for UTF validity unless PCRE2_NO_UTF_CHECK is set. An
invalid UTF replacement string causes an immediate return with the rel-
evant UTF error code.
- If PCRE2_SUBSTITUTE_LITERAL is set, the replacement string is not in-
+ If PCRE2_SUBSTITUTE_LITERAL is set, the replacement string is not in-
terpreted in any way. By default, however, a dollar character is an es-
- cape character that can specify the insertion of characters from cap-
- ture groups and names from (*MARK) or other control verbs in the pat-
+ cape character that can specify the insertion of characters from cap-
+ ture groups and names from (*MARK) or other control verbs in the pat-
tern. The following forms are always recognized:
$$ insert a dollar character
@@ -3334,18 +3364,18 @@
$<n> or ${<n>} insert the contents of group <n>
$*MARK or ${*MARK} insert a control verb name
- Either a group number or a group name can be given for <n>. Curly
- brackets are required only if the following character would be inter-
+ Either a group number or a group name can be given for <n>. Curly
+ brackets are required only if the following character would be inter-
preted as part of the number or name. The number may be zero to include
- the entire matched string. For example, if the pattern a(b)c is
- matched with "=abc=" and the replacement string "+$1$0$1+", the result
+ the entire matched string. For example, if the pattern a(b)c is
+ matched with "=abc=" and the replacement string "+$1$0$1+", the result
is "=+babcb+=".
- $*MARK inserts the name from the last encountered backtracking control
- verb on the matching path that has a name. (*MARK) must always include
- a name, but the other verbs need not. For example, in the case of
+ $*MARK inserts the name from the last encountered backtracking control
+ verb on the matching path that has a name. (*MARK) must always include
+ a name, but the other verbs need not. For example, in the case of
(*MARK:A)(*PRUNE) the name inserted is "A", but for (*MARK:A)(*PRUNE:B)
- the relevant name is "B". This facility can be used to perform simple
+ the relevant name is "B". This facility can be used to perform simple
simultaneous substitutions, as this pcre2test example shows:
/(*MARK:pear)apple|(*MARK:orange)lemon/g,replace=${*MARK}
@@ -3353,15 +3383,15 @@
2: pear orange
PCRE2_SUBSTITUTE_GLOBAL causes the function to iterate over the subject
- string, replacing every matching substring. If this option is not set,
- only the first matching substring is replaced. The search for matches
- takes place in the original subject string (that is, previous replace-
- ments do not affect it). Iteration is implemented by advancing the
- startoffset value for each search, which is always passed the entire
+ string, replacing every matching substring. If this option is not set,
+ only the first matching substring is replaced. The search for matches
+ takes place in the original subject string (that is, previous replace-
+ ments do not affect it). Iteration is implemented by advancing the
+ startoffset value for each search, which is always passed the entire
subject string. If an offset limit is set in the match context, search-
ing stops when that limit is reached.
- You can restrict the effect of a global substitution to a portion of
+ You can restrict the effect of a global substitution to a portion of
the subject string by setting either or both of startoffset and an off-
set limit. Here is a pcre2test example:
@@ -3369,73 +3399,73 @@
ABC ABC ABC ABC\=offset=3,offset_limit=12
2: ABC A!C A!C ABC
- When continuing with global substitutions after matching a substring
+ When continuing with global substitutions after matching a substring
with zero length, an attempt to find a non-empty match at the same off-
set is performed. If this is not successful, the offset is advanced by
one character except when CRLF is a valid newline sequence and the next
- two characters are CR, LF. In this case, the offset is advanced by two
+ two characters are CR, LF. In this case, the offset is advanced by two
characters.
PCRE2_SUBSTITUTE_UNKNOWN_UNSET causes references to capture groups that
do not appear in the pattern to be treated as unset groups. This option
- should be used with care, because it means that a typo in a group name
+ should be used with care, because it means that a typo in a group name
or number no longer causes the PCRE2_ERROR_NOSUBSTRING error.
PCRE2_SUBSTITUTE_UNSET_EMPTY causes unset capture groups (including un-
- known groups when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) to be treated
- as empty strings when inserted as described above. If this option is
+ known groups when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) to be treated
+ as empty strings when inserted as described above. If this option is
not set, an attempt to insert an unset group causes the PCRE2_ERROR_UN-
- SET error. This option does not influence the extended substitution
+ SET error. This option does not influence the extended substitution
syntax described below.
- PCRE2_SUBSTITUTE_EXTENDED causes extra processing to be applied to the
- replacement string. Without this option, only the dollar character is
- special, and only the group insertion forms listed above are valid.
+ PCRE2_SUBSTITUTE_EXTENDED causes extra processing to be applied to the
+ replacement string. Without this option, only the dollar character is
+ special, and only the group insertion forms listed above are valid.
When PCRE2_SUBSTITUTE_EXTENDED is set, two things change:
- Firstly, backslash in a replacement string is interpreted as an escape
+ Firstly, backslash in a replacement string is interpreted as an escape
character. The usual forms such as \n or \x{ddd} can be used to specify
- particular character codes, and backslash followed by any non-alphanu-
- meric character quotes that character. Extended quoting can be coded
+ particular character codes, and backslash followed by any non-alphanu-
+ meric character quotes that character. Extended quoting can be coded
using \Q...\E, exactly as in pattern strings.
- There are also four escape sequences for forcing the case of inserted
- letters. The insertion mechanism has three states: no case forcing,
+ There are also four escape sequences for forcing the case of inserted
+ letters. The insertion mechanism has three states: no case forcing,
force upper case, and force lower case. The escape sequences change the
current state: \U and \L change to upper or lower case forcing, respec-
- tively, and \E (when not terminating a \Q quoted sequence) reverts to
- no case forcing. The sequences \u and \l force the next character (if
- it is a letter) to upper or lower case, respectively, and then the
+ tively, and \E (when not terminating a \Q quoted sequence) reverts to
+ no case forcing. The sequences \u and \l force the next character (if
+ it is a letter) to upper or lower case, respectively, and then the
state automatically reverts to no case forcing. Case forcing applies to
- all inserted characters, including those from capture groups and let-
- ters within \Q...\E quoted sequences. If either PCRE2_UTF or PCRE2_UCP
- was set when the pattern was compiled, Unicode properties are used for
+ all inserted characters, including those from capture groups and let-
+ ters within \Q...\E quoted sequences. If either PCRE2_UTF or PCRE2_UCP
+ was set when the pattern was compiled, Unicode properties are used for
case forcing characters whose code points are greater than 127.
Note that case forcing sequences such as \U...\E do not nest. For exam-
- ple, the result of processing "\Uaa\LBB\Ecc\E" is "AAbbcc"; the final
- \E has no effect. Note also that the PCRE2_ALT_BSUX and PCRE2_EX-
+ ple, the result of processing "\Uaa\LBB\Ecc\E" is "AAbbcc"; the final
+ \E has no effect. Note also that the PCRE2_ALT_BSUX and PCRE2_EX-
TRA_ALT_BSUX options do not apply to replacement strings.
- The second effect of setting PCRE2_SUBSTITUTE_EXTENDED is to add more
- flexibility to capture group substitution. The syntax is similar to
+ The second effect of setting PCRE2_SUBSTITUTE_EXTENDED is to add more
+ flexibility to capture group substitution. The syntax is similar to
that used by Bash:
${<n>:-<string>}
${<n>:+<string1>:<string2>}
- As before, <n> may be a group number or a name. The first form speci-
- fies a default value. If group <n> is set, its value is inserted; if
- not, <string> is expanded and the result inserted. The second form
- specifies strings that are expanded and inserted when group <n> is set
- or unset, respectively. The first form is just a convenient shorthand
+ As before, <n> may be a group number or a name. The first form speci-
+ fies a default value. If group <n> is set, its value is inserted; if
+ not, <string> is expanded and the result inserted. The second form
+ specifies strings that are expanded and inserted when group <n> is set
+ or unset, respectively. The first form is just a convenient shorthand
for
${<n>:+${<n>}:<string>}
- Backslash can be used to escape colons and closing curly brackets in
- the replacement strings. A change of the case forcing state within a
- replacement string remains in force afterwards, as shown in this
+ Backslash can be used to escape colons and closing curly brackets in
+ the replacement strings. A change of the case forcing state within a
+ replacement string remains in force afterwards, as shown in this
pcre2test example:
/(some)?(body)/substitute_extended,replace=${1:+\U:\L}HeLLo
@@ -3444,8 +3474,8 @@
somebody
1: HELLO
- The PCRE2_SUBSTITUTE_UNSET_EMPTY option does not affect these extended
- substitutions. However, PCRE2_SUBSTITUTE_UNKNOWN_UNSET does cause un-
+ The PCRE2_SUBSTITUTE_UNSET_EMPTY option does not affect these extended
+ substitutions. However, PCRE2_SUBSTITUTE_UNKNOWN_UNSET does cause un-
known groups in the extended syntax forms to be treated as unset.
If PCRE2_SUBSTITUTE_LITERAL is set, PCRE2_SUBSTITUTE_UNKNOWN_UNSET,
@@ -3454,8 +3484,8 @@
Substitution errors
- In the event of an error, pcre2_substitute() returns a negative error
- code. Except for PCRE2_ERROR_NOMATCH (which is never returned), errors
+ In the event of an error, pcre2_substitute() returns a negative error
+ code. Except for PCRE2_ERROR_NOMATCH (which is never returned), errors
from pcre2_match() are passed straight back.
PCRE2_ERROR_NOSUBSTRING is returned for a non-existent substring inser-
@@ -3462,29 +3492,29 @@
tion, unless PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set.
PCRE2_ERROR_UNSET is returned for an unset substring insertion (includ-
- ing an unknown substring when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set)
- when the simple (non-extended) syntax is used and PCRE2_SUBSTITUTE_UN-
+ ing an unknown substring when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set)
+ when the simple (non-extended) syntax is used and PCRE2_SUBSTITUTE_UN-
SET_EMPTY is not set.
- PCRE2_ERROR_NOMEMORY is returned if the output buffer is not big
+ PCRE2_ERROR_NOMEMORY is returned if the output buffer is not big
enough. If the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option is set, the size
- of buffer that is needed is returned via outlengthptr. Note that this
+ of buffer that is needed is returned via outlengthptr. Note that this
does not happen by default.
PCRE2_ERROR_NULL is returned if PCRE2_SUBSTITUTE_MATCHED is set but the
match_data argument is NULL.
- PCRE2_ERROR_BADREPLACEMENT is used for miscellaneous syntax errors in
- the replacement string, with more particular errors being PCRE2_ER-
+ PCRE2_ERROR_BADREPLACEMENT is used for miscellaneous syntax errors in
+ the replacement string, with more particular errors being PCRE2_ER-
ROR_BADREPESCAPE (invalid escape sequence), PCRE2_ERROR_REPMISSINGBRACE
- (closing curly bracket not found), PCRE2_ERROR_BADSUBSTITUTION (syntax
- error in extended group substitution), and PCRE2_ERROR_BADSUBSPATTERN
+ (closing curly bracket not found), PCRE2_ERROR_BADSUBSTITUTION (syntax
+ error in extended group substitution), and PCRE2_ERROR_BADSUBSPATTERN
(the pattern match ended before it started or the match started earlier
- than the current position in the subject, which can happen if \K is
+ than the current position in the subject, which can happen if \K is
used in an assertion).
As for all PCRE2 errors, a text message that describes the error can be
- obtained by calling the pcre2_get_error_message() function (see "Ob-
+ obtained by calling the pcre2_get_error_message() function (see "Ob-
taining a textual error message" above).
Substitution callouts
@@ -3493,15 +3523,15 @@
int (*callout_function)(pcre2_substitute_callout_block *, void *),
void *callout_data);
- The pcre2_set_substitution_callout() function can be used to specify a
- callout function for pcre2_substitute(). This information is passed in
+ The pcre2_set_substitution_callout() function can be used to specify a
+ callout function for pcre2_substitute(). This information is passed in
a match context. The callout function is called after each substitution
has been processed, but it can cause the replacement not to happen. The
- callout function is not called for simulated substitutions that happen
+ callout function is not called for simulated substitutions that happen
as a result of the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option.
The first argument of the callout function is a pointer to a substitute
- callout block structure, which contains the following fields, not nec-
+ callout block structure, which contains the following fields, not nec-
essarily in this order:
uint32_t version;
@@ -3512,9 +3542,9 @@
uint32_t oveccount;
PCRE2_SIZE output_offsets[2];
- The version field contains the version number of the block format. The
- current version is 0. The version number will increase in future if
- more fields are added, but the intention is never to remove any of the
+ The version field contains the version number of the block format. The
+ current version is 0. The version number will increase in future if
+ more fields are added, but the intention is never to remove any of the
existing fields.
The subscount field is the number of the current match. It is 1 for the
@@ -3521,25 +3551,25 @@
first callout, 2 for the second, and so on. The input and output point-
ers are copies of the values passed to pcre2_substitute().
- The ovector field points to the ovector, which contains the result of
+ The ovector field points to the ovector, which contains the result of
the most recent match. The oveccount field contains the number of pairs
that are set in the ovector, and is always greater than zero.
- The output_offsets vector contains the offsets of the replacement in
- the output string. This has already been processed for dollar and (if
+ The output_offsets vector contains the offsets of the replacement in
+ the output string. This has already been processed for dollar and (if
requested) backslash substitutions as described above.
- The second argument of the callout function is the value passed as
- callout_data when the function was registered. The value returned by
+ The second argument of the callout function is the value passed as
+ callout_data when the function was registered. The value returned by
the callout function is interpreted as follows:
- If the value is zero, the replacement is accepted, and, if PCRE2_SUB-
- STITUTE_GLOBAL is set, processing continues with a search for the next
- match. If the value is not zero, the current replacement is not ac-
- cepted. If the value is greater than zero, processing continues when
- PCRE2_SUBSTITUTE_GLOBAL is set. Otherwise (the value is less than zero
- or PCRE2_SUBSTITUTE_GLOBAL is not set), the the rest of the input is
- copied to the output and the call to pcre2_substitute() exits, return-
+ If the value is zero, the replacement is accepted, and, if PCRE2_SUB-
+ STITUTE_GLOBAL is set, processing continues with a search for the next
+ match. If the value is not zero, the current replacement is not ac-
+ cepted. If the value is greater than zero, processing continues when
+ PCRE2_SUBSTITUTE_GLOBAL is set. Otherwise (the value is less than zero
+ or PCRE2_SUBSTITUTE_GLOBAL is not set), the the rest of the input is
+ copied to the output and the call to pcre2_substitute() exits, return-
ing the number of matches so far.
@@ -3548,56 +3578,56 @@
int pcre2_substring_nametable_scan(const pcre2_code *code,
PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);
- When a pattern is compiled with the PCRE2_DUPNAMES option, names for
- capture groups are not required to be unique. Duplicate names are al-
- ways allowed for groups with the same number, created by using the (?|
+ When a pattern is compiled with the PCRE2_DUPNAMES option, names for
+ capture groups are not required to be unique. Duplicate names are al-
+ ways allowed for groups with the same number, created by using the (?|
feature. Indeed, if such groups are named, they are required to use the
same names.
- Normally, patterns that use duplicate names are such that in any one
- match, only one of each set of identically-named groups participates.
+ Normally, patterns that use duplicate names are such that in any one
+ match, only one of each set of identically-named groups participates.
An example is shown in the pcre2pattern documentation.
- When duplicates are present, pcre2_substring_copy_byname() and
- pcre2_substring_get_byname() return the first substring corresponding
- to the given name that is set. Only if none are set is PCRE2_ERROR_UN-
- SET is returned. The pcre2_substring_number_from_name() function re-
- turns the error PCRE2_ERROR_NOUNIQUESUBSTRING when there are duplicate
+ When duplicates are present, pcre2_substring_copy_byname() and
+ pcre2_substring_get_byname() return the first substring corresponding
+ to the given name that is set. Only if none are set is PCRE2_ERROR_UN-
+ SET is returned. The pcre2_substring_number_from_name() function re-
+ turns the error PCRE2_ERROR_NOUNIQUESUBSTRING when there are duplicate
names.
- If you want to get full details of all captured substrings for a given
- name, you must use the pcre2_substring_nametable_scan() function. The
- first argument is the compiled pattern, and the second is the name. If
- the third and fourth arguments are NULL, the function returns a group
+ If you want to get full details of all captured substrings for a given
+ name, you must use the pcre2_substring_nametable_scan() function. The
+ first argument is the compiled pattern, and the second is the name. If
+ the third and fourth arguments are NULL, the function returns a group
number for a unique name, or PCRE2_ERROR_NOUNIQUESUBSTRING otherwise.
When the third and fourth arguments are not NULL, they must be pointers
- to variables that are updated by the function. After it has run, they
+ to variables that are updated by the function. After it has run, they
point to the first and last entries in the name-to-number table for the
- given name, and the function returns the length of each entry in code
- units. In both cases, PCRE2_ERROR_NOSUBSTRING is returned if there are
+ given name, and the function returns the length of each entry in code
+ units. In both cases, PCRE2_ERROR_NOSUBSTRING is returned if there are
no entries for the given name.
The format of the name table is described above in the section entitled
- Information about a pattern. Given all the relevant entries for the
- name, you can extract each of their numbers, and hence the captured
+ Information about a pattern. Given all the relevant entries for the
+ name, you can extract each of their numbers, and hence the captured
data.
FINDING ALL POSSIBLE MATCHES AT ONE POSITION
- The traditional matching function uses a similar algorithm to Perl,
- which stops when it finds the first match at a given point in the sub-
+ The traditional matching function uses a similar algorithm to Perl,
+ which stops when it finds the first match at a given point in the sub-
ject. If you want to find all possible matches, or the longest possible
- match at a given position, consider using the alternative matching
- function (see below) instead. If you cannot use the alternative func-
+ match at a given position, consider using the alternative matching
+ function (see below) instead. If you cannot use the alternative func-
tion, you can kludge it up by making use of the callout facility, which
is described in the pcre2callout documentation.
What you have to do is to insert a callout right at the end of the pat-
- tern. When your callout function is called, extract and save the cur-
- rent matched substring. Then return 1, which forces pcre2_match() to
- backtrack and try other alternatives. Ultimately, when it runs out of
+ tern. When your callout function is called, extract and save the cur-
+ rent matched substring. Then return 1, which forces pcre2_match() to
+ backtrack and try other alternatives. Ultimately, when it runs out of
matches, pcre2_match() will yield PCRE2_ERROR_NOMATCH.
@@ -3609,26 +3639,26 @@
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);
- The function pcre2_dfa_match() is called to match a subject string
- against a compiled pattern, using a matching algorithm that scans the
+ The function pcre2_dfa_match() is called to match a subject string
+ against a compiled pattern, using a matching algorithm that scans the
subject string just once (not counting lookaround assertions), and does
- not backtrack. This has different characteristics to the normal algo-
- rithm, and is not compatible with Perl. Some of the features of PCRE2
- patterns are not supported. Nevertheless, there are times when this
- kind of matching can be useful. For a discussion of the two matching
+ not backtrack. This has different characteristics to the normal algo-
+ rithm, and is not compatible with Perl. Some of the features of PCRE2
+ patterns are not supported. Nevertheless, there are times when this
+ kind of matching can be useful. For a discussion of the two matching
algorithms, and a list of features that pcre2_dfa_match() does not sup-
port, see the pcre2matching documentation.
- The arguments for the pcre2_dfa_match() function are the same as for
+ The arguments for the pcre2_dfa_match() function are the same as for
pcre2_match(), plus two extras. The ovector within the match data block
is used in a different way, and this is described below. The other com-
- mon arguments are used in the same way as for pcre2_match(), so their
+ mon arguments are used in the same way as for pcre2_match(), so their
description is not repeated here.
- The two additional arguments provide workspace for the function. The
- workspace vector should contain at least 20 elements. It is used for
+ The two additional arguments provide workspace for the function. The
+ workspace vector should contain at least 20 elements. It is used for
keeping track of multiple paths through the pattern tree. More
- workspace is needed for patterns and subjects where there are a lot of
+ workspace is needed for patterns and subjects where there are a lot of
potential matches.
Here is an example of a simple call to pcre2_dfa_match():
@@ -3648,45 +3678,45 @@
Option bits for pcre_dfa_match()
- The unused bits of the options argument for pcre2_dfa_match() must be
- zero. The only bits that may be set are PCRE2_ANCHORED,
- PCRE2_COPY_MATCHED_SUBJECT, PCRE2_ENDANCHORED, PCRE2_NOTBOL, PCRE2_NO-
+ The unused bits of the options argument for pcre2_dfa_match() must be
+ zero. The only bits that may be set are PCRE2_ANCHORED,
+ PCRE2_COPY_MATCHED_SUBJECT, PCRE2_ENDANCHORED, PCRE2_NOTBOL, PCRE2_NO-
TEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_UTF_CHECK,
- PCRE2_PARTIAL_HARD, PCRE2_PARTIAL_SOFT, PCRE2_DFA_SHORTEST, and
- PCRE2_DFA_RESTART. All but the last four of these are exactly the same
+ PCRE2_PARTIAL_HARD, PCRE2_PARTIAL_SOFT, PCRE2_DFA_SHORTEST, and
+ PCRE2_DFA_RESTART. All but the last four of these are exactly the same
as for pcre2_match(), so their description is not repeated here.
PCRE2_PARTIAL_HARD
PCRE2_PARTIAL_SOFT
- These have the same general effect as they do for pcre2_match(), but
- the details are slightly different. When PCRE2_PARTIAL_HARD is set for
- pcre2_dfa_match(), it returns PCRE2_ERROR_PARTIAL if the end of the
+ These have the same general effect as they do for pcre2_match(), but
+ the details are slightly different. When PCRE2_PARTIAL_HARD is set for
+ pcre2_dfa_match(), it returns PCRE2_ERROR_PARTIAL if the end of the
subject is reached and there is still at least one matching possibility
that requires additional characters. This happens even if some complete
- matches have already been found. When PCRE2_PARTIAL_SOFT is set, the
- return code PCRE2_ERROR_NOMATCH is converted into PCRE2_ERROR_PARTIAL
- if the end of the subject is reached, there have been no complete
+ matches have already been found. When PCRE2_PARTIAL_SOFT is set, the
+ return code PCRE2_ERROR_NOMATCH is converted into PCRE2_ERROR_PARTIAL
+ if the end of the subject is reached, there have been no complete
matches, but there is still at least one matching possibility. The por-
- tion of the string that was inspected when the longest partial match
+ tion of the string that was inspected when the longest partial match
was found is set as the first matching string in both cases. There is a
- more detailed discussion of partial and multi-segment matching, with
+ more detailed discussion of partial and multi-segment matching, with
examples, in the pcre2partial documentation.
PCRE2_DFA_SHORTEST
- Setting the PCRE2_DFA_SHORTEST option causes the matching algorithm to
+ Setting the PCRE2_DFA_SHORTEST option causes the matching algorithm to
stop as soon as it has found one match. Because of the way the alterna-
- tive algorithm works, this is necessarily the shortest possible match
+ tive algorithm works, this is necessarily the shortest possible match
at the first possible matching point in the subject string.
PCRE2_DFA_RESTART
- When pcre2_dfa_match() returns a partial match, it is possible to call
+ When pcre2_dfa_match() returns a partial match, it is possible to call
it again, with additional subject characters, and have it continue with
the same match. The PCRE2_DFA_RESTART option requests this action; when
- it is set, the workspace and wscount options must reference the same
- vector as before because data about the match so far is left in them
+ it is set, the workspace and wscount options must reference the same
+ vector as before because data about the match so far is left in them
after a partial match. There is more discussion of this facility in the
pcre2partial documentation.
@@ -3694,8 +3724,8 @@
When pcre2_dfa_match() succeeds, it may have matched more than one sub-
string in the subject. Note, however, that all the matches from one run
- of the function start at the same point in the subject. The shorter
- matches are all initial substrings of the longer matches. For example,
+ of the function start at the same point in the subject. The shorter
+ matches are all initial substrings of the longer matches. For example,
if the pattern
<.*>
@@ -3710,80 +3740,80 @@
<something> <something else>
<something>
- On success, the yield of the function is a number greater than zero,
- which is the number of matched substrings. The offsets of the sub-
- strings are returned in the ovector, and can be extracted by number in
- the same way as for pcre2_match(), but the numbers bear no relation to
- any capture groups that may exist in the pattern, because DFA matching
+ On success, the yield of the function is a number greater than zero,
+ which is the number of matched substrings. The offsets of the sub-
+ strings are returned in the ovector, and can be extracted by number in
+ the same way as for pcre2_match(), but the numbers bear no relation to
+ any capture groups that may exist in the pattern, because DFA matching
does not support capturing.
- Calls to the convenience functions that extract substrings by name re-
+ Calls to the convenience functions that extract substrings by name re-
turn the error PCRE2_ERROR_DFA_UFUNC (unsupported function) if used af-
- ter a DFA match. The convenience functions that extract substrings by
+ ter a DFA match. The convenience functions that extract substrings by
number never return PCRE2_ERROR_NOSUBSTRING.
- The matched strings are stored in the ovector in reverse order of
- length; that is, the longest matching string is first. If there were
- too many matches to fit into the ovector, the yield of the function is
+ The matched strings are stored in the ovector in reverse order of
+ length; that is, the longest matching string is first. If there were
+ too many matches to fit into the ovector, the yield of the function is
zero, and the vector is filled with the longest matches.
- NOTE: PCRE2's "auto-possessification" optimization usually applies to
- character repeats at the end of a pattern (as well as internally). For
- example, the pattern "a\d+" is compiled as if it were "a\d++". For DFA
- matching, this means that only one possible match is found. If you re-
+ NOTE: PCRE2's "auto-possessification" optimization usually applies to
+ character repeats at the end of a pattern (as well as internally). For
+ example, the pattern "a\d+" is compiled as if it were "a\d++". For DFA
+ matching, this means that only one possible match is found. If you re-
ally do want multiple matches in such cases, either use an ungreedy re-
- peat such as "a\d+?" or set the PCRE2_NO_AUTO_POSSESS option when com-
+ peat such as "a\d+?" or set the PCRE2_NO_AUTO_POSSESS option when com-
piling.
Error returns from pcre2_dfa_match()
The pcre2_dfa_match() function returns a negative number when it fails.
- Many of the errors are the same as for pcre2_match(), as described
+ Many of the errors are the same as for pcre2_match(), as described
above. There are in addition the following errors that are specific to
pcre2_dfa_match():
PCRE2_ERROR_DFA_UITEM
- This return is given if pcre2_dfa_match() encounters an item in the
- pattern that it does not support, for instance, the use of \C in a UTF
+ This return is given if pcre2_dfa_match() encounters an item in the
+ pattern that it does not support, for instance, the use of \C in a UTF
mode or a backreference.
PCRE2_ERROR_DFA_UCOND
- This return is given if pcre2_dfa_match() encounters a condition item
+ This return is given if pcre2_dfa_match() encounters a condition item
that uses a backreference for the condition, or a test for recursion in
a specific capture group. These are not supported.
PCRE2_ERROR_DFA_UINVALID_UTF
- This return is given if pcre2_dfa_match() is called for a pattern that
- was compiled with PCRE2_MATCH_INVALID_UTF. This is not supported for
+ This return is given if pcre2_dfa_match() is called for a pattern that
+ was compiled with PCRE2_MATCH_INVALID_UTF. This is not supported for
DFA matching.
PCRE2_ERROR_DFA_WSSIZE
- This return is given if pcre2_dfa_match() runs out of space in the
+ This return is given if pcre2_dfa_match() runs out of space in the
workspace vector.
PCRE2_ERROR_DFA_RECURSE
When a recursion or subroutine call is processed, the matching function
- calls itself recursively, using private memory for the ovector and
- workspace. This error is given if the internal ovector is not large
- enough. This should be extremely rare, as a vector of size 1000 is
+ calls itself recursively, using private memory for the ovector and
+ workspace. This error is given if the internal ovector is not large
+ enough. This should be extremely rare, as a vector of size 1000 is
used.
PCRE2_ERROR_DFA_BADRESTART
- When pcre2_dfa_match() is called with the PCRE2_DFA_RESTART option,
- some plausibility checks are made on the contents of the workspace,
- which should contain data about the previous partial match. If any of
+ When pcre2_dfa_match() is called with the PCRE2_DFA_RESTART option,
+ some plausibility checks are made on the contents of the workspace,
+ which should contain data about the previous partial match. If any of
these checks fail, this error is given.
SEE ALSO
- pcre2build(3), pcre2callout(3), pcre2demo(3), pcre2matching(3),
+ pcre2build(3), pcre2callout(3), pcre2demo(3), pcre2matching(3),
pcre2partial(3), pcre2posix(3), pcre2sample(3), pcre2unicode(3).
@@ -3796,7 +3826,7 @@
REVISION
- Last updated: 05 October 2020
+ Last updated: 04 November 2020
Copyright (c) 1997-2020 University of Cambridge.
------------------------------------------------------------------------------
Modified: code/trunk/doc/pcre2api.3
===================================================================
--- code/trunk/doc/pcre2api.3 2020-11-03 13:20:09 UTC (rev 1281)
+++ code/trunk/doc/pcre2api.3 2020-11-04 17:01:13 UTC (rev 1282)
@@ -1,4 +1,4 @@
-.TH PCRE2API 3 "05 October 2020" "PCRE2 10.36"
+.TH PCRE2API 3 "04 November 2020" "PCRE2 10.36"
.SH NAME
PCRE2 - Perl-compatible regular expressions (revised API)
.sp
@@ -564,14 +564,15 @@
.P
In a more complicated situation, where patterns are compiled only when they are
first needed, but are still shared between threads, pointers to compiled
-patterns must be protected from simultaneous writing by multiple threads, at
-least until a pattern has been compiled. The logic can be something like this:
+patterns must be protected from simultaneous writing by multiple threads. This
+is somewhat tricky to do correctly. If you know that writing to a pointer is
+atomic in your environment, you can use logic like this:
.sp
Get a read-only (shared) lock (mutex) for pointer
if (pointer == NULL)
{
Get a write (unique) lock for pointer
- pointer = pcre2_compile(...
+ if (pointer == NULL) pointer = pcre2_compile(...
}
Release the lock
Use pointer in pcre2_match()
@@ -578,10 +579,38 @@
.sp
Of course, testing for compilation errors should also be included in the code.
.P
-If JIT is being used, but the JIT compilation is not being done immediately,
-(perhaps waiting to see if the pattern is used often enough) similar logic is
-required. JIT compilation updates a pointer within the compiled code block, so
-a thread must gain unique write access to the pointer before calling
+The reason for checking the pointer a second time is as follows: Several
+threads may have acquired the shared lock and tested the pointer for being
+NULL, but only one of them will be given the write lock, with the rest kept
+waiting. The winning thread will compile the pattern and store the result.
+After this thread releases the write lock, another thread will get it, and if
+it does not retest pointer for being NULL, will recompile the pattern and
+overwrite the pointer, creating a memory leak and possibly causing other
+issues.
+.P
+In an environment where writing to a pointer may not be atomic, the above logic
+is not sufficient. The thread that is doing the compiling may be descheduled
+after writing only part of the pointer, which could cause other threads to use
+an invalid value. Instead of checking the pointer itself, a separate "pointer
+is valid" flag (that can be updated atomically) must be used:
+.sp
+ Get a read-only (shared) lock (mutex) for pointer
+ if (!pointer_is_valid)
+ {
+ Get a write (unique) lock for pointer
+ if (!pointer_is_valid)
+ {
+ pointer = pcre2_compile(...
+ pointer_is_valid = TRUE
+ }
+ }
+ Release the lock
+ Use pointer in pcre2_match()
+.sp
+If JIT is being used, but the JIT compilation is not being done immediately
+(perhaps waiting to see if the pattern is used often enough), similar logic is
+required. JIT compilation updates a value within the compiled code block, so a
+thread must gain unique write access to the pointer before calling
\fBpcre2_jit_compile()\fP. Alternatively, \fBpcre2_code_copy()\fP or
\fBpcre2_code_copy_with_tables()\fP can be used to obtain a private copy of the
compiled code before calling the JIT compiler.
@@ -3971,6 +4000,6 @@
.rs
.sp
.nf
-Last updated: 05 October 2020
+Last updated: 04 November 2020
Copyright (c) 1997-2020 University of Cambridge.
.fi
