Revision: 1163
http://www.exim.org/viewvc/pcre2?view=rev&revision=1163
Author: ph10
Date: 2019-09-04 19:14:54 +0100 (Wed, 04 Sep 2019)
Log Message:
-----------
Back off failed attempt to handle nested lookbehinds for estimating how much of
a partial match to retain for multi-segment matching. Document the current
difficulty if the whole first segment cannot be retained.
Modified Paths:
--------------
code/trunk/ChangeLog
code/trunk/doc/html/pcre2api.html
code/trunk/doc/html/pcre2partial.html
code/trunk/doc/pcre2.txt
code/trunk/doc/pcre2api.3
code/trunk/doc/pcre2partial.3
code/trunk/src/pcre2_compile.c
code/trunk/testdata/testoutput15
code/trunk/testdata/testoutput2
Modified: code/trunk/ChangeLog
===================================================================
--- code/trunk/ChangeLog 2019-09-04 07:23:01 UTC (rev 1162)
+++ code/trunk/ChangeLog 2019-09-04 18:14:54 UTC (rev 1163)
@@ -66,12 +66,7 @@
parenthesized item may contain multiple branches or other backtracking points,
for example /(a|ab){1}+c/ or /(a+){1}+a/.
-13. Nested lookbehinds are now taken into account when computing the maximum
-lookbehind value. For example /(?<=a(?<=ba)c)/ previously set a maximum
-lookbehind of 2, because that is the largest individual lookbehind. Now it sets
-it to 3, because matching looks back 3 characters.
-
-14. For partial matches, pcre2test was always showing the maximum lookbehind
+13. For partial matches, pcre2test was always showing the maximum lookbehind
characters, flagged with "<", which is misleading when the lookbehind didn't
actually look behind the start (because it was later in the pattern). Showing
all consulted preceding characters for partial matches is now controlled by the
@@ -79,25 +74,25 @@
available only for non-JIT matching, because JIT does not maintain the first
and last consulted characters.
-15. DFA matching (using pcre2_dfa_match()) was not recognising a partial match
+14. DFA matching (using pcre2_dfa_match()) was not recognising a partial match
if the end of the subject was encountered in a lookahead (conditional or
otherwise), an atomic group, or a recursion.
-16. Give error if pcre2test -t, -T, -tm or -TM is given an argument of zero.
+15. Give error if pcre2test -t, -T, -tm or -TM is given an argument of zero.
-17. Check for integer overflow when computing lookbehind lengths. Fixes
+16. Check for integer overflow when computing lookbehind lengths. Fixes
Clusterfuzz issue 15636.
-18. Implemented non-atomic positive lookaround assertions.
+17. Implemented non-atomic positive lookaround assertions.
-19. If a lookbehind contained a lookahead that contained another lookbehind
+18. If a lookbehind contained a lookahead that contained another lookbehind
within it, the nested lookbehind was not correctly processed. For example, if
/(?<=(?=(?<=a)))b/ was matched to "ab" it gave no match instead of matching
"b".
-20. Implemented pcre2_get_match_data_size().
+19. Implemented pcre2_get_match_data_size().
-21. Two alterations to partial matching (not yet done by JIT):
+20. Two alterations to partial matching (not yet done by JIT):
(a) The definition of a partial match is slightly changed: if a pattern
contains any lookbehinds, an empty partial match may be given, because this
@@ -111,29 +106,29 @@
(c) An empty string partial hard match can be returned for \z and \Z as it
is documented that they shouldn't match.
-22. A branch that started with (*ACCEPT) was not being recognized as one that
+21. A branch that started with (*ACCEPT) was not being recognized as one that
could match an empty string.
-23. Corrected pcre2_set_character_tables() tables data type: was const unsigned
+22. Corrected pcre2_set_character_tables() tables data type: was const unsigned
char * instead of const uint8_t *, as generated by pcre2_maketables().
-24. Upgraded to Unicode 12.1.0.
+23. Upgraded to Unicode 12.1.0.
-25. Add -jitfast command line option to pcre2test (to make all the jit options
+24. Add -jitfast command line option to pcre2test (to make all the jit options
available directly).
-26. Make pcre2test -C show if libreadline or libedit is supported.
+25. Make pcre2test -C show if libreadline or libedit is supported.
-28. If the length of one branch of a group exceeded 65535 (the maximum value
+26. If the length of one branch of a group exceeded 65535 (the maximum value
that is remembered as a minimum length), the whole group's length was
incorrectly recorded as 65535, leading to incorrect "no match" when start-up
optimizations were in force.
-29. The "rightmost consulted character" value was not always correct; in
+27. The "rightmost consulted character" value was not always correct; in
particular, if a pattern ended with a negative lookahead, characters that were
inspected in that lookahead were not included.
-30. Add the pcre2_maketables_free() function.
+28. Add the pcre2_maketables_free() function.
Version 10.33 16-April-2019
Modified: code/trunk/doc/html/pcre2api.html
===================================================================
--- code/trunk/doc/html/pcre2api.html 2019-09-04 07:23:01 UTC (rev 1162)
+++ code/trunk/doc/html/pcre2api.html 2019-09-04 18:14:54 UTC (rev 1163)
@@ -2272,26 +2272,24 @@
<pre>
PCRE2_INFO_MAXLOOKBEHIND
</pre>
-Return the largest number of characters (not code units) before the current
-matching point that could be inspected while processing a lookbehind assertion
-in the pattern. Before release 10.34 this request used to give the largest
-value for any individual assertion. Now it takes into account nested
-lookbehinds, which can mean that the overall value is greater. For example, the
-pattern (?<=a(?<=ba)c) previously returned 2, because that is the length of the
-largest individual lookbehind. Now it returns 3, because matching actually
-looks back 3 characters.
+A lookbehind assertion moves back a certain number of characters (not code
+units) when it starts to process each of its branches. This request returns the
+largest of these backward moves. The third argument should point to a uint32_t
+integer. The simple assertions \b and \B require 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.
</P>
<P>
-The third argument should point to a uint32_t integer. This information is
-useful when doing multi-segment matching using the partial matching facilities.
-Note that the simple assertions \b and \B require a one-character lookbehind.
-\A also registers a one-character lookbehind, though it does not actually
-inspect the previous character. This is to ensure that at least one character
-from the old segment is retained when a new segment is processed. Otherwise, if
-there are no lookbehinds in the pattern, \A might match incorrectly at the
-start of a second or subsequent segment. There are more details in the
+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 processed, the
+first lookbehind moves back by two characters, matches one character, then the
+nested lookbehind also moves back by two characters. This puts the matching
+point three characters earlier than it was at the start.
+PCRE2_INFO_MAXLOOKBEHIND is really only useful as a debugging tool. See the
<a href="pcre2partial.html"><b>pcre2partial</b></a>
-documentation.
+documentation for a discussion of multi-segment matching.
<pre>
PCRE2_INFO_MINLENGTH
</pre>
Modified: code/trunk/doc/html/pcre2partial.html
===================================================================
--- code/trunk/doc/html/pcre2partial.html 2019-09-04 07:23:01 UTC (rev 1162)
+++ code/trunk/doc/html/pcre2partial.html 2019-09-04 18:14:54 UTC (rev 1163)
@@ -49,7 +49,7 @@
function. If both options are set, PCRE2_PARTIAL_HARD takes precedence.
</P>
<P>
-If you want to use partial matching with just-in-time optimized code, as well
+If you want to use partial matching with just-in-time optimized code, as well
as setting a partial match option for the matching function, you must also call
<b>pcre2_jit_compile()</b> with one or both of these options:
<pre>
@@ -101,7 +101,7 @@
</P>
<P>
(2) The pattern contains one or more lookbehind assertions. This condition
-exists in case there is a lookbehind that inspects characters before the start
+exists in case there is a lookbehind that inspects characters before the start
of the match.
</P>
<P>
@@ -171,7 +171,7 @@
partial match is found, without continuing to search for possible complete
matches. This option is "hard" because it prefers an earlier partial match over
a later complete match. For this reason, the assumption is made that the end of
-the supplied subject string is not the true end of the available data, which is
+the supplied subject string is not the true end of the available data, which is
why \z, \Z, \b, \B, and $ always give a partial match.
</P>
<P>
@@ -226,7 +226,7 @@
data> 3juj\=ph
No match
</pre>
-This example gives the same results for both hard and soft partial matching
+This example gives the same results for both hard and soft partial matching
options. Here is an example where there is a difference:
<pre>
re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
@@ -234,7 +234,7 @@
0: 25jun04
1: jun
data> 25jun04\=ph
- Partial match: 25jun04
+ Partial match: 25jun04
</pre>
With PCRE2_PARTIAL_SOFT, the subject is matched completely. For
PCRE2_PARTIAL_HARD, however, the subject is assumed not to be complete, so
@@ -244,9 +244,12 @@
<P>
PCRE was not originally designed with multi-segment matching in mind. However,
over time, features (including partial matching) that make multi-segment
-matching possible have been added. The string is searched segment by segment by
-calling <b>pcre2_match()</b> repeatedly, with the aim of achieving the same
-results that would happen if the entire string was available for searching.
+matching possible have been added. A very long string can be searched segment
+by segment by calling <b>pcre2_match()</b> repeatedly, with the aim of achieving
+the same results that would happen if the entire string was available for
+searching all the time. Normally, the strings that are being sought are much
+shorter than each individual segment, and are in the middle of very long
+strings, so the pattern is normally not anchored.
</P>
<P>
Special logic must be implemented to handle a matched substring that spans a
@@ -256,11 +259,10 @@
also be set for all but the first segment.
</P>
<P>
-When a partial match occurs, the next segment must be added to the current
-subject and the match re-run, using the <i>startoffset</i> argument of
+When a partial match occurs, the next segment must be added to the current
+subject and the match re-run, using the <i>startoffset</i> argument of
<b>pcre2_match()</b> to begin at the point where the partial match started.
-Multi-segment matching is usually used to search for substrings in the middle
-of very long sequences, so the patterns are normally not anchored. For example:
+For example:
<pre>
re> /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/
data> ...the date is 23ja\=ph
@@ -269,43 +271,24 @@
0: 23jan19
1: jan
</pre>
-Note the use of the <b>offset</b> modifier to start the new match where the
-partial match was found.
+Note the use of the <b>offset</b> modifier to start the new match where the
+partial match was found. In this example, the next segment was added to the one
+in which the partial match was found. This is the most straightforward
+approach, typically using a memory buffer that is twice the size of each
+segment. After a partial match, the first half of the buffer is discarded, the
+second half is moved to the start of the buffer, and a new segment is added
+before repeating the match as in the example above. After a no match, the
+entire buffer can be discarded.
</P>
<P>
-In this simple example, the next segment was just added to the one in which the
-partial match was found. However, if there are memory constraints, it may be
-necessary to discard text that precedes the partial match before adding the
-next segment. In cases such as the above, where the pattern does not contain
-any lookbehinds, it is sufficient to retain only the partially matched
-substring. However, if a pattern contains a lookbehind assertion, characters
+If there are memory constraints, you may want to discard text that precedes a
+partial match before adding the next segment. Unfortunately, this is not at
+present straightforward. In cases such as the above, where the pattern does not
+contain any lookbehinds, it is sufficient to retain only the partially matched
+substring. However, if the pattern contains a lookbehind assertion, characters
that precede the start of the partial match may have been inspected during the
-matching process.
-</P>
-<P>
-The only lookbehind information that is available is the length of the longest
-lookbehind in a pattern. This may not, of course, be at the start of the
-pattern, but retaining that many characters before the partial match is
-sufficient, if not always strictly necessary. The way to do this is as follows:
-</P>
-<P>
-Before doing any matching, find the length of the longest lookbehind in the
-pattern by calling <b>pcre2_pattern_info()</b> with the PCRE2_INFO_MAXLOOKBEHIND
-option. Note that the resulting count is in characters, not code units. After a
-partial match, moving back from the ovector[0] offset in the subject by the
-number of characters given for the maximum lookbehind gets you to the earliest
-character that must be retained. In a non-UTF or a 32-bit situation, moving
-back is just a subtraction, but in UTF-8 or UTF-16 you have to count characters
-while moving back through the code units. Characters before the point you have
-now reached can be discarded.
-</P>
-<P>
-For example, if the pattern "(?<=123)abc" is partially matched against the
-string "xx123ab", the ovector offsets are 5 and 7 ("ab"). The maximum
-lookbehind count is 3, so all characters before offset 2 can be discarded. The
-value of <b>startoffset</b> for the next match should be 3. When <b>pcre2test</b>
-displays a partial match, it indicates the lookbehind characters with '<'
-characters if the <b>allusedtext</b> modifier is set:
+matching process. When <b>pcre2test</b> displays a partial match, it indicates
+these characters with '<' if the <b>allusedtext</b> modifier is set:
<pre>
re> "(?<=123)abc"
data> xx123ab\=ph,allusedtext
@@ -312,9 +295,29 @@
Partial match: 123ab
<<<
</pre>
-Note that the \fPallusedtext\fP modifier is not available for JIT matching,
-because JIT matching does not maintain the first and last consulted characters.
+However, the \fPallusedtext\fP modifier is not available for JIT matching,
+because JIT matching does not record the first (or last) consulted characters.
+For this reason, this information is not available via the API. It is therefore
+not possible in general to obtain the exact number of characters that must be
+retained in order to get the right match result. If you cannot retain the
+entire segment, you must find some heuristic way of choosing.
</P>
+<P>
+If you know the approximate length of the matching substrings, you can use that
+to decide how much text to retain. The only lookbehind information that is
+currently available via the API is the length of the longest individual
+lookbehind in a pattern, but this can be misleading if there are nested
+lookbehinds. The value returned by calling <b>pcre2_pattern_info()</b> with the
+PCRE2_INFO_MAXLOOKBEHIND option is the maximum number of characters (not code
+units) that any individual lookbehind moves back when it is processed. A
+pattern such as "(?<=(?<!b)a)" has a maximum lookbehind value of one, but
+inspects two characters before its starting point.
+</P>
+<P>
+In a non-UTF or a 32-bit case, moving back is just a subtraction, but in
+UTF-8 or UTF-16 you have to count characters while moving back through the code
+units.
+</P>
<br><a name="SEC5" href="#TOC1">PARTIAL MATCHING USING pcre2_dfa_match()</a><br>
<P>
The DFA function moves along the subject string character by character, without
@@ -379,11 +382,11 @@
</P>
<P>
If you do want to allow for starting again at the next character, one way of
-doing it is to retain the matched part of the segment and try a new complete
-match, as described for <b>pcre2_match()</b> above. Another possibility is to
-work with two buffers. If a partial match at offset <i>n</i> in the first buffer
-is followed by "no match" when PCRE2_DFA_RESTART is used on the second buffer,
-you can then try a new match starting at offset <i>n+1</i> in the first buffer.
+doing it is to retain some or all of the segment and try a new complete match,
+as described for <b>pcre2_match()</b> above. Another possibility is to work with
+two buffers. If a partial match at offset <i>n</i> in the first buffer is
+followed by "no match" when PCRE2_DFA_RESTART is used on the second buffer, you
+can then try a new match starting at offset <i>n+1</i> in the first buffer.
</P>
<br><a name="SEC7" href="#TOC1">AUTHOR</a><br>
<P>
@@ -396,7 +399,7 @@
</P>
<br><a name="SEC8" href="#TOC1">REVISION</a><br>
<P>
-Last updated: 07 August 2019
+Last updated: 04 September 2019
<br>
Copyright © 1997-2019 University of Cambridge.
<br>
Modified: code/trunk/doc/pcre2.txt
===================================================================
--- code/trunk/doc/pcre2.txt 2019-09-04 07:23:01 UTC (rev 1162)
+++ code/trunk/doc/pcre2.txt 2019-09-04 18:14:54 UTC (rev 1163)
@@ -2234,35 +2234,34 @@
PCRE2_INFO_MAXLOOKBEHIND
- Return the largest number of characters (not code units) before the
- current matching point that could be inspected while processing a look-
- behind assertion in the pattern. Before release 10.34 this request used
- to give the largest value for any individual assertion. Now it takes
- into account nested lookbehinds, which can mean that the overall value
- is greater. For example, the pattern (?<=a(?<=ba)c) previously returned
- 2, because that is the length of the largest individual lookbehind. Now
- it returns 3, because matching actually looks back 3 characters.
+ 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
+ character.
- The third argument should point to a uint32_t integer. This information
- is useful when doing multi-segment matching using the partial matching
- facilities. Note that the simple assertions \b and \B require a one-
- character lookbehind. \A also registers a one-character lookbehind,
- though it does not actually inspect the previous character. This is to
- ensure that at least one character from the old segment is retained
- when a new segment is processed. Otherwise, if there are no lookbehinds
- in the pattern, \A might match incorrectly at the start of a second or
- subsequent segment. There are more details in the pcre2partial documen-
- tation.
+ 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-
+ 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
+ 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
@@ -2270,44 +2269,44 @@
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) -
@@ -2314,7 +2313,7 @@
(?<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 ??:
@@ -2323,8 +2322,8 @@
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
@@ -2343,14 +2342,14 @@
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.
@@ -2361,30 +2360,30 @@
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.
@@ -2398,58 +2397,58 @@
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.
@@ -2460,15 +2459,15 @@
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():
@@ -2483,7 +2482,7 @@
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.
@@ -2490,110 +2489,110 @@
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.
@@ -2600,9 +2599,9 @@
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.
@@ -2609,67 +2608,67 @@
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
@@ -2676,22 +2675,22 @@
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.
@@ -2701,38 +2700,38 @@
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.
@@ -2743,82 +2742,82 @@
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.
@@ -2828,25 +2827,25 @@
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:
@@ -2853,30 +2852,30 @@
^(*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.
@@ -2883,14 +2882,14 @@
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
@@ -2899,20 +2898,20 @@
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
@@ -2926,15 +2925,15 @@
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
@@ -2947,7 +2946,7 @@
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
@@ -2954,7 +2953,7 @@
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
@@ -2963,11 +2962,11 @@
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
@@ -2976,12 +2975,12 @@
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.
@@ -2990,20 +2989,20 @@
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.
@@ -3022,39 +3021,39 @@
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
@@ -3063,25 +3062,25 @@
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
@@ -3092,8 +3091,8 @@
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.
@@ -3104,31 +3103,31 @@
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().
@@ -3148,7 +3147,7 @@
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+)...
@@ -3156,32 +3155,32 @@
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.
@@ -3194,54 +3193,54 @@
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
PCRE2_SIZE *outlengthptr);
- This function calls pcre2_match() and then makes a copy of the subject
- string in outputbuffer, replacing one or more parts that were matched
+ This function calls pcre2_match() and then makes a copy of the subject
+ string in outputbuffer, replacing one or more 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.
- The default is to perform just one replacement, but there is an option
- that requests multiple replacements (see PCRE2_SUBSTITUTE_GLOBAL below
+ can be given as PCRE2_ZERO_TERMINATED for a zero-terminated string.
+ The default is to perform just one replacement, but there is an option
+ that requests multiple replacements (see PCRE2_SUBSTITUTE_GLOBAL below
for details).
- 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 an external match_data block is provided, its contents afterwards
- are those set by the final call to pcre2_match(). For global changes,
- this will have ended in a matching error. The contents of the ovector
+ If an external match_data block is provided, its contents afterwards
+ are those set by the final call to pcre2_match(). For global changes,
+ this will have ended in a matching error. The contents of the ovector
within the match data block may or may not have been changed.
- The outlengthptr argument must point to a variable that contains the
- length, in code units, of the output buffer. If the function is suc-
- cessful, the value is updated to contain the length of the new string,
+ The outlengthptr argument must point to a variable that contains the
+ length, in code units, of the output buffer. If the function is suc-
+ cessful, the value is updated to contain the length 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 (see below), in which case
- the value is the minimum length needed, including space for the trail-
+ the value is the minimum length needed, including space for the trail-
ing zero. Note that in order to compute the required length, pcre2_sub-
stitute() has to simulate all the matching and copying, instead of giv-
ing an error return as soon as the buffer overflows. Note also that the
length is in code units, not bytes.
- In the replacement string, which is interpreted as a UTF string in UTF
+ In the replacement string, which is interpreted as a UTF string in UTF
mode, and is checked for UTF validity unless the PCRE2_NO_UTF_CHECK op-
tion is set, a dollar character is an escape character that can specify
- the insertion of characters from capture groups or names from (*MARK)
- or other control verbs in the pattern. The following forms are always
+ the insertion of characters from capture groups or names from (*MARK)
+ or other control verbs in the pattern. The following forms are always
recognized:
$$ insert a dollar character
@@ -3248,18 +3247,18 @@
$<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}
@@ -3266,19 +3265,19 @@
apple lemon
2: pear orange
- As well as the usual options for pcre2_match(), a number of additional
+ As well as the usual options for pcre2_match(), a number of additional
options can be set in the options argument of pcre2_substitute().
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:
@@ -3286,87 +3285,87 @@
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_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.
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-
+ all inserted characters, including those from capture groups and let-
ters within \Q...\E quoted sequences.
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 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
@@ -3375,16 +3374,16 @@
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 successful, pcre2_substitute() returns the number of successful
- matches. This may be zero if no matches were found, and is never
+ If successful, pcre2_substitute() returns the number of successful
+ matches. This may be zero if no matches were found, and is never
greater than 1 unless PCRE2_SUBSTITUTE_GLOBAL is set.
In the event of an error, a negative error code is returned. Except for
- PCRE2_ERROR_NOMATCH (which is never returned), errors from
+ 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-
@@ -3391,26 +3390,26 @@
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_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
@@ -3419,15 +3418,15 @@
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;
@@ -3438,9 +3437,9 @@
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
@@ -3447,25 +3446,25 @@
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.
@@ -3474,56 +3473,56 @@
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.
@@ -3535,26 +3534,26 @@
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():
@@ -3574,45 +3573,45 @@
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.
@@ -3620,8 +3619,8 @@
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
<.*>
@@ -3636,80 +3635,80 @@
<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).
@@ -5877,23 +5876,24 @@
PCRE was not originally designed with multi-segment matching in mind.
However, over time, features (including partial matching) that make
- multi-segment matching possible have been added. The string is searched
- segment by segment by calling pcre2_match() repeatedly, with the aim of
- achieving the same results that would happen if the entire string was
- available for searching.
+ multi-segment matching possible have been added. A very long string can
+ be searched segment by segment by calling pcre2_match() repeatedly,
+ with the aim of achieving the same results that would happen if the en-
+ tire string was available for searching all the time. Normally, the
+ strings that are being sought are much shorter than each individual
+ segment, and are in the middle of very long strings, so the pattern is
+ normally not anchored.
- Special logic must be implemented to handle a matched substring that
+ Special logic must be implemented to handle a matched substring that
spans a segment boundary. PCRE2_PARTIAL_HARD should be used, because it
- returns a partial match at the end of a segment whenever there is the
- possibility of changing the match by adding more characters. The
+ returns a partial match at the end of a segment whenever there is the
+ possibility of changing the match by adding more characters. The
PCRE2_NOTBOL option should also be set for all but the first segment.
When a partial match occurs, the next segment must be added to the cur-
- rent subject and the match re-run, using the startoffset argument of
- pcre2_match() to begin at the point where the partial match started.
- Multi-segment matching is usually used to search for substrings in the
- middle of very long sequences, so the patterns are normally not an-
- chored. For example:
+ rent subject and the match re-run, using the startoffset argument of
+ pcre2_match() to begin at the point where the partial match started.
+ For example:
re> /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/
data> ...the date is 23ja\=ph
@@ -5902,75 +5902,77 @@
0: 23jan19
1: jan
- Note the use of the offset modifier to start the new match where the
- partial match was found.
+ Note the use of the offset modifier to start the new match where the
+ partial match was found. In this example, the next segment was added to
+ the one in which the partial match was found. This is the most
+ straightforward approach, typically using a memory buffer that is twice
+ the size of each segment. After a partial match, the first half of the
+ buffer is discarded, the second half is moved to the start of the buf-
+ fer, and a new segment is added before repeating the match as in the
+ example above. After a no match, the entire buffer can be discarded.
- In this simple example, the next segment was just added to the one in
- which the partial match was found. However, if there are memory con-
- straints, it may be necessary to discard text that precedes the partial
- match before adding the next segment. In cases such as the above, where
- the pattern does not contain any lookbehinds, it is sufficient to re-
- tain only the partially matched substring. However, if a pattern con-
- tains a lookbehind assertion, characters that precede the start of the
- partial match may have been inspected during the matching process.
+ If there are memory constraints, you may want to discard text that pre-
+ cedes a partial match before adding the next segment. Unfortunately,
+ this is not at present straightforward. In cases such as the above,
+ where the pattern does not contain any lookbehinds, it is sufficient to
+ retain only the partially matched substring. However, if the pattern
+ contains a lookbehind assertion, characters that precede the start of
+ the partial match may have been inspected during the matching process.
+ When pcre2test displays a partial match, it indicates these characters
+ with '<' if the allusedtext modifier is set:
- The only lookbehind information that is available is the length of the
- longest lookbehind in a pattern. This may not, of course, be at the
- start of the pattern, but retaining that many characters before the
- partial match is sufficient, if not always strictly necessary. The way
- to do this is as follows:
-
- Before doing any matching, find the length of the longest lookbehind in
- the pattern by calling pcre2_pattern_info() with the
- PCRE2_INFO_MAXLOOKBEHIND option. Note that the resulting count is in
- characters, not code units. After a partial match, moving back from the
- ovector[0] offset in the subject by the number of characters given for
- the maximum lookbehind gets you to the earliest character that must be
- retained. In a non-UTF or a 32-bit situation, moving back is just a
- subtraction, but in UTF-8 or UTF-16 you have to count characters while
- moving back through the code units. Characters before the point you
- have now reached can be discarded.
-
- For example, if the pattern "(?<=123)abc" is partially matched against
- the string "xx123ab", the ovector offsets are 5 and 7 ("ab"). The maxi-
- mum lookbehind count is 3, so all characters before offset 2 can be
- discarded. The value of startoffset for the next match should be 3.
- When pcre2test displays a partial match, it indicates the lookbehind
- characters with '<' characters if the allusedtext modifier is set:
-
re> "(?<=123)abc"
data> xx123ab\=ph,allusedtext
Partial match: 123ab
<<<
- Note that the allusedtext modifier is not available for JIT matching,
- because JIT matching does not maintain the first and last consulted
- characters.
+ However, the allusedtext modifier is not available for JIT matching,
+ because JIT matching does not record the first (or last) consulted
+ characters. For this reason, this information is not available via the
+ API. It is therefore not possible in general to obtain the exact number
+ of characters that must be retained in order to get the right match re-
+ sult. If you cannot retain the entire segment, you must find some
+ heuristic way of choosing.
+ If you know the approximate length of the matching substrings, you can
+ use that to decide how much text to retain. The only lookbehind infor-
+ mation that is currently available via the API is the length of the
+ longest individual lookbehind in a pattern, but this can be misleading
+ if there are nested lookbehinds. The value returned by calling
+ pcre2_pattern_info() with the PCRE2_INFO_MAXLOOKBEHIND option is the
+ maximum number of characters (not code units) that any individual look-
+ behind moves back when it is processed. A pattern such as
+ "(?<=(?<!b)a)" has a maximum lookbehind value of one, but inspects two
+ characters before its starting point.
+ In a non-UTF or a 32-bit case, moving back is just a subtraction, but
+ in UTF-8 or UTF-16 you have to count characters while moving back
+ through the code units.
+
+
PARTIAL MATCHING USING pcre2_dfa_match()
The DFA function moves along the subject string character by character,
- without backtracking, searching for all possible matches simultane-
- ously. If the end of the subject is reached before the end of the pat-
+ without backtracking, searching for all possible matches simultane-
+ ously. If the end of the subject is reached before the end of the pat-
tern, there is the possibility of a partial match.
When PCRE2_PARTIAL_SOFT is set, PCRE2_ERROR_PARTIAL is returned only if
- there have been no complete matches. Otherwise, the complete matches
- are returned. If PCRE2_PARTIAL_HARD is set, a partial match takes
- precedence over any complete matches. The portion of the string that
- was matched when the longest partial match was found is set as the
+ there have been no complete matches. Otherwise, the complete matches
+ are returned. If PCRE2_PARTIAL_HARD is set, a partial match takes
+ precedence over any complete matches. The portion of the string that
+ was matched when the longest partial match was found is set as the
first matching string.
- Because the DFA function always searches for all possible matches, and
- there is no difference between greedy and ungreedy repetition, its be-
- haviour is different from the pcre2_match(). Consider the string "dog"
+ Because the DFA function always searches for all possible matches, and
+ there is no difference between greedy and ungreedy repetition, its be-
+ haviour is different from the pcre2_match(). Consider the string "dog"
matched against this ungreedy pattern:
/dog(sbody)??/
- Whereas the standard function stops as soon as it finds the complete
- match for "dog", the DFA function also finds the partial match for
+ Whereas the standard function stops as soon as it finds the complete
+ match for "dog", the DFA function also finds the partial match for
"dogsbody", and so returns that when PCRE2_PARTIAL_HARD is set.
@@ -5977,12 +5979,12 @@
MULTI-SEGMENT MATCHING WITH pcre2_dfa_match()
When a partial match has been found using the DFA matching function, it
- is possible to continue the match by providing additional subject data
- and calling the function again with the same compiled regular expres-
+ is possible to continue the match by providing additional subject data
+ and calling the function again with the same compiled regular expres-
sion, this time setting the PCRE2_DFA_RESTART option. You must pass the
same working space as before, because this is where details of the pre-
- vious partial match are stored. You can set the PCRE2_PARTIAL_SOFT or
- PCRE2_PARTIAL_HARD options with PCRE2_DFA_RESTART to continue partial
+ vious partial match are stored. You can set the PCRE2_PARTIAL_SOFT or
+ PCRE2_PARTIAL_HARD options with PCRE2_DFA_RESTART to continue partial
matching over multiple segments. Here is an example using pcre2test:
re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
@@ -5991,33 +5993,33 @@
data> n05\=dfa,dfa_restart
0: n05
- The first call has "23ja" as the subject, and requests partial match-
- ing; the second call has "n05" as the subject for the continued
- (restarted) match. Notice that when the match is complete, only the
- last part is shown; PCRE2 does not retain the previously partially-
- matched string. It is up to the calling program to do that if it needs
- to. This means that, for an unanchored pattern, if a continued match
- fails, it is not possible to try again at a new starting point. All
+ The first call has "23ja" as the subject, and requests partial match-
+ ing; the second call has "n05" as the subject for the continued
+ (restarted) match. Notice that when the match is complete, only the
+ last part is shown; PCRE2 does not retain the previously partially-
+ matched string. It is up to the calling program to do that if it needs
+ to. This means that, for an unanchored pattern, if a continued match
+ fails, it is not possible to try again at a new starting point. All
this facility is capable of doing is continuing with the previous match
attempt. For example, consider this pattern:
1234|3789
- If the first part of the subject is "ABC123", a partial match of the
- first alternative is found at offset 3. There is no partial match for
+ If the first part of the subject is "ABC123", a partial match of the
+ first alternative is found at offset 3. There is no partial match for
the second alternative, because such a match does not start at the same
- point in the subject string. Attempting to continue with the string
- "7890" does not yield a match because only those alternatives that
- match at one point in the subject are remembered. Depending on the ap-
+ point in the subject string. Attempting to continue with the string
+ "7890" does not yield a match because only those alternatives that
+ match at one point in the subject are remembered. Depending on the ap-
plication, this may or may not be what you want.
- If you do want to allow for starting again at the next character, one
- way of doing it is to retain the matched part of the segment and try a
- new complete match, as described for pcre2_match() above. Another pos-
- sibility is to work with two buffers. If a partial match at offset n in
- the first buffer is followed by "no match" when PCRE2_DFA_RESTART is
- used on the second buffer, you can then try a new match starting at
- offset n+1 in the first buffer.
+ If you do want to allow for starting again at the next character, one
+ way of doing it is to retain some or all of the segment and try a new
+ complete match, as described for pcre2_match() above. Another possibil-
+ ity is to work with two buffers. If a partial match at offset n in the
+ first buffer is followed by "no match" when PCRE2_DFA_RESTART is used
+ on the second buffer, you can then try a new match starting at offset
+ n+1 in the first buffer.
AUTHOR
@@ -6029,7 +6031,7 @@
REVISION
- Last updated: 07 August 2019
+ Last updated: 04 September 2019
Copyright (c) 1997-2019 University of Cambridge.
------------------------------------------------------------------------------
Modified: code/trunk/doc/pcre2api.3
===================================================================
--- code/trunk/doc/pcre2api.3 2019-09-04 07:23:01 UTC (rev 1162)
+++ code/trunk/doc/pcre2api.3 2019-09-04 18:14:54 UTC (rev 1163)
@@ -2232,27 +2232,25 @@
.sp
PCRE2_INFO_MAXLOOKBEHIND
.sp
-Return the largest number of characters (not code units) before the current
-matching point that could be inspected while processing a lookbehind assertion
-in the pattern. Before release 10.34 this request used to give the largest
-value for any individual assertion. Now it takes into account nested
-lookbehinds, which can mean that the overall value is greater. For example, the
-pattern (?<=a(?<=ba)c) previously returned 2, because that is the length of the
-largest individual lookbehind. Now it returns 3, because matching actually
-looks back 3 characters.
+A lookbehind assertion moves back a certain number of characters (not code
+units) when it starts to process each of its branches. This request returns the
+largest of these backward moves. The third argument should point to a uint32_t
+integer. The simple assertions \eb and \eB require a one-character lookbehind
+and cause PCRE2_INFO_MAXLOOKBEHIND to return 1 in the absence of anything
+longer. \eA also registers a one-character lookbehind, though it does not
+actually inspect the previous character.
.P
-The third argument should point to a uint32_t integer. This information is
-useful when doing multi-segment matching using the partial matching facilities.
-Note that the simple assertions \eb and \eB require a one-character lookbehind.
-\eA also registers a one-character lookbehind, though it does not actually
-inspect the previous character. This is to ensure that at least one character
-from the old segment is retained when a new segment is processed. Otherwise, if
-there are no lookbehinds in the pattern, \eA might match incorrectly at the
-start of a second or subsequent segment. There are more details in the
+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 processed, the
+first lookbehind moves back by two characters, matches one character, then the
+nested lookbehind also moves back by two characters. This puts the matching
+point three characters earlier than it was at the start.
+PCRE2_INFO_MAXLOOKBEHIND is really only useful as a debugging tool. See the
.\" HREF
\fBpcre2partial\fP
.\"
-documentation.
+documentation for a discussion of multi-segment matching.
.sp
PCRE2_INFO_MINLENGTH
.sp
Modified: code/trunk/doc/pcre2partial.3
===================================================================
--- code/trunk/doc/pcre2partial.3 2019-09-04 07:23:01 UTC (rev 1162)
+++ code/trunk/doc/pcre2partial.3 2019-09-04 18:14:54 UTC (rev 1163)
@@ -1,4 +1,4 @@
-.TH PCRE2PARTIAL 3 "07 August 2019" "PCRE2 10.34"
+.TH PCRE2PARTIAL 3 "04 September 2019" "PCRE2 10.34"
.SH NAME
PCRE2 - Perl-compatible regular expressions
.SH "PARTIAL MATCHING IN PCRE2"
@@ -25,7 +25,7 @@
complete match, though the details differ between the two types of matching
function. If both options are set, PCRE2_PARTIAL_HARD takes precedence.
.P
-If you want to use partial matching with just-in-time optimized code, as well
+If you want to use partial matching with just-in-time optimized code, as well
as setting a partial match option for the matching function, you must also call
\fBpcre2_jit_compile()\fP with one or both of these options:
.sp
@@ -73,7 +73,7 @@
matched string.
.P
(2) The pattern contains one or more lookbehind assertions. This condition
-exists in case there is a lookbehind that inspects characters before the start
+exists in case there is a lookbehind that inspects characters before the start
of the match.
.P
(3) There is a special case when the whole pattern can match an empty string.
@@ -139,7 +139,7 @@
partial match is found, without continuing to search for possible complete
matches. This option is "hard" because it prefers an earlier partial match over
a later complete match. For this reason, the assumption is made that the end of
-the supplied subject string is not the true end of the available data, which is
+the supplied subject string is not the true end of the available data, which is
why \ez, \eZ, \eb, \eB, and $ always give a partial match.
.P
If PCRE2_PARTIAL_SOFT is set, the partial match is remembered, but matching
@@ -192,7 +192,7 @@
data> 3juj\e=ph
No match
.sp
-This example gives the same results for both hard and soft partial matching
+This example gives the same results for both hard and soft partial matching
options. Here is an example where there is a difference:
.sp
re> /^\ed?\ed(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\ed\ed$/
@@ -200,8 +200,8 @@
0: 25jun04
1: jun
data> 25jun04\e=ph
- Partial match: 25jun04
-.sp
+ Partial match: 25jun04
+.sp
With PCRE2_PARTIAL_SOFT, the subject is matched completely. For
PCRE2_PARTIAL_HARD, however, the subject is assumed not to be complete, so
there is only a partial match.
@@ -213,9 +213,12 @@
.sp
PCRE was not originally designed with multi-segment matching in mind. However,
over time, features (including partial matching) that make multi-segment
-matching possible have been added. The string is searched segment by segment by
-calling \fBpcre2_match()\fP repeatedly, with the aim of achieving the same
-results that would happen if the entire string was available for searching.
+matching possible have been added. A very long string can be searched segment
+by segment by calling \fBpcre2_match()\fP repeatedly, with the aim of achieving
+the same results that would happen if the entire string was available for
+searching all the time. Normally, the strings that are being sought are much
+shorter than each individual segment, and are in the middle of very long
+strings, so the pattern is normally not anchored.
.P
Special logic must be implemented to handle a matched substring that spans a
segment boundary. PCRE2_PARTIAL_HARD should be used, because it returns a
@@ -223,11 +226,10 @@
changing the match by adding more characters. The PCRE2_NOTBOL option should
also be set for all but the first segment.
.P
-When a partial match occurs, the next segment must be added to the current
-subject and the match re-run, using the \fIstartoffset\fP argument of
+When a partial match occurs, the next segment must be added to the current
+subject and the match re-run, using the \fIstartoffset\fP argument of
\fBpcre2_match()\fP to begin at the point where the partial match started.
-Multi-segment matching is usually used to search for substrings in the middle
-of very long sequences, so the patterns are normally not anchored. For example:
+For example:
.sp
re> /\ed?\ed(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\ed\ed/
data> ...the date is 23ja\e=ph
@@ -236,50 +238,51 @@
0: 23jan19
1: jan
.sp
-Note the use of the \fBoffset\fP modifier to start the new match where the
-partial match was found.
+Note the use of the \fBoffset\fP modifier to start the new match where the
+partial match was found. In this example, the next segment was added to the one
+in which the partial match was found. This is the most straightforward
+approach, typically using a memory buffer that is twice the size of each
+segment. After a partial match, the first half of the buffer is discarded, the
+second half is moved to the start of the buffer, and a new segment is added
+before repeating the match as in the example above. After a no match, the
+entire buffer can be discarded.
.P
-In this simple example, the next segment was just added to the one in which the
-partial match was found. However, if there are memory constraints, it may be
-necessary to discard text that precedes the partial match before adding the
-next segment. In cases such as the above, where the pattern does not contain
-any lookbehinds, it is sufficient to retain only the partially matched
-substring. However, if a pattern contains a lookbehind assertion, characters
+If there are memory constraints, you may want to discard text that precedes a
+partial match before adding the next segment. Unfortunately, this is not at
+present straightforward. In cases such as the above, where the pattern does not
+contain any lookbehinds, it is sufficient to retain only the partially matched
+substring. However, if the pattern contains a lookbehind assertion, characters
that precede the start of the partial match may have been inspected during the
-matching process.
-.P
-The only lookbehind information that is available is the length of the longest
-lookbehind in a pattern. This may not, of course, be at the start of the
-pattern, but retaining that many characters before the partial match is
-sufficient, if not always strictly necessary. The way to do this is as follows:
-.P
-Before doing any matching, find the length of the longest lookbehind in the
-pattern by calling \fBpcre2_pattern_info()\fP with the PCRE2_INFO_MAXLOOKBEHIND
-option. Note that the resulting count is in characters, not code units. After a
-partial match, moving back from the ovector[0] offset in the subject by the
-number of characters given for the maximum lookbehind gets you to the earliest
-character that must be retained. In a non-UTF or a 32-bit situation, moving
-back is just a subtraction, but in UTF-8 or UTF-16 you have to count characters
-while moving back through the code units. Characters before the point you have
-now reached can be discarded.
-.P
-For example, if the pattern "(?<=123)abc" is partially matched against the
-string "xx123ab", the ovector offsets are 5 and 7 ("ab"). The maximum
-lookbehind count is 3, so all characters before offset 2 can be discarded. The
-value of \fBstartoffset\fP for the next match should be 3. When \fBpcre2test\fP
-displays a partial match, it indicates the lookbehind characters with '<'
-characters if the \fBallusedtext\fP modifier is set:
+matching process. When \fBpcre2test\fP displays a partial match, it indicates
+these characters with '<' if the \fBallusedtext\fP modifier is set:
.sp
re> "(?<=123)abc"
data> xx123ab\e=ph,allusedtext
Partial match: 123ab
<<<
-.sp
-Note that the \fPallusedtext\fP modifier is not available for JIT matching,
-because JIT matching does not maintain the first and last consulted characters.
+.sp
+However, the \fPallusedtext\fP modifier is not available for JIT matching,
+because JIT matching does not record the first (or last) consulted characters.
+For this reason, this information is not available via the API. It is therefore
+not possible in general to obtain the exact number of characters that must be
+retained in order to get the right match result. If you cannot retain the
+entire segment, you must find some heuristic way of choosing.
+.P
+If you know the approximate length of the matching substrings, you can use that
+to decide how much text to retain. The only lookbehind information that is
+currently available via the API is the length of the longest individual
+lookbehind in a pattern, but this can be misleading if there are nested
+lookbehinds. The value returned by calling \fBpcre2_pattern_info()\fP with the
+PCRE2_INFO_MAXLOOKBEHIND option is the maximum number of characters (not code
+units) that any individual lookbehind moves back when it is processed. A
+pattern such as "(?<=(?<!b)a)" has a maximum lookbehind value of one, but
+inspects two characters before its starting point.
+.P
+In a non-UTF or a 32-bit case, moving back is just a subtraction, but in
+UTF-8 or UTF-16 you have to count characters while moving back through the code
+units.
.
.
-.
.SH "PARTIAL MATCHING USING pcre2_dfa_match()"
.rs
.sp
@@ -344,11 +347,11 @@
want.
.P
If you do want to allow for starting again at the next character, one way of
-doing it is to retain the matched part of the segment and try a new complete
-match, as described for \fBpcre2_match()\fP above. Another possibility is to
-work with two buffers. If a partial match at offset \fIn\fP in the first buffer
-is followed by "no match" when PCRE2_DFA_RESTART is used on the second buffer,
-you can then try a new match starting at offset \fIn+1\fP in the first buffer.
+doing it is to retain some or all of the segment and try a new complete match,
+as described for \fBpcre2_match()\fP above. Another possibility is to work with
+two buffers. If a partial match at offset \fIn\fP in the first buffer is
+followed by "no match" when PCRE2_DFA_RESTART is used on the second buffer, you
+can then try a new match starting at offset \fIn+1\fP in the first buffer.
.
.
.SH AUTHOR
@@ -365,6 +368,6 @@
.rs
.sp
.nf
-Last updated: 07 August 2019
+Last updated: 04 September 2019
Copyright (c) 1997-2019 University of Cambridge.
.fi
Modified: code/trunk/src/pcre2_compile.c
===================================================================
--- code/trunk/src/pcre2_compile.c 2019-09-04 07:23:01 UTC (rev 1162)
+++ code/trunk/src/pcre2_compile.c 2019-09-04 18:14:54 UTC (rev 1163)
@@ -128,12 +128,12 @@
compile_block *, PCRE2_SIZE *);
static int
- get_branchlength(uint32_t **, int *, int *, int *, parsed_recurse_check *,
+ get_branchlength(uint32_t **, int *, int *, parsed_recurse_check *,
compile_block *);
static BOOL
- set_lookbehind_lengths(uint32_t **, int *, int *, int *,
- parsed_recurse_check *, compile_block *);
+ set_lookbehind_lengths(uint32_t **, int *, int *, parsed_recurse_check *,
+ compile_block *);
static int
check_lookbehinds(uint32_t *, uint32_t **, parsed_recurse_check *,
@@ -398,9 +398,6 @@
#define GI_SET_FIXED_LENGTH 0x80000000u
#define GI_NOT_FIXED_LENGTH 0x40000000u
#define GI_FIXED_LENGTH_MASK 0x0000ffffu
-#define GI_EXTRA_MASK 0x0fff0000u
-#define GI_EXTRA_MAX 0xfff /* NB not unsigned */
-#define GI_EXTRA_SHIFT 16
/* This simple test for a decimal digit works for both ASCII/Unicode and EBCDIC
and is fast (a good compiler can turn it into a subtraction and unsigned
@@ -8897,7 +8894,6 @@
Arguments:
pptrptr pointer to pointer in the parsed pattern
isinline FALSE if a reference or recursion; TRUE for inline group
- extraptr pointer to where to return extra lookbehind length
errcodeptr pointer to the errorcode
lcptr pointer to the loop counter
group number of captured group or -1 for a non-capturing group
@@ -8908,13 +8904,11 @@
*/
static int
-get_grouplength(uint32_t **pptrptr, BOOL isinline, int *extraptr,
- int *errcodeptr, int *lcptr, int group, parsed_recurse_check *recurses,
- compile_block *cb)
+get_grouplength(uint32_t **pptrptr, BOOL isinline, int *errcodeptr, int *lcptr,
+ int group, parsed_recurse_check *recurses, compile_block *cb)
{
int branchlength;
int grouplength = -1;
-int extra = 0;
/* The cache can be used only if there is no possibility of there being two
groups with the same number. We do not need to set the end pointer for a group
@@ -8928,7 +8922,6 @@
if ((groupinfo & GI_SET_FIXED_LENGTH) != 0)
{
if (isinline) *pptrptr = parsed_skip(*pptrptr, PSKIP_KET);
- *extraptr = (groupinfo & GI_EXTRA_MASK) >> GI_EXTRA_SHIFT;
return groupinfo & GI_FIXED_LENGTH_MASK;
}
}
@@ -8937,28 +8930,16 @@
for(;;)
{
- int branchextra;
- branchlength = get_branchlength(pptrptr, &branchextra, errcodeptr, lcptr,
- recurses, cb);
+ branchlength = get_branchlength(pptrptr, errcodeptr, lcptr, recurses, cb);
if (branchlength < 0) goto ISNOTFIXED;
- if (grouplength == -1)
- {
- grouplength = branchlength;
- extra = branchextra;
- }
- else if (grouplength != branchlength || extra != branchextra) goto ISNOTFIXED;
+ if (grouplength == -1) grouplength = branchlength;
+ else if (grouplength != branchlength) goto ISNOTFIXED;
if (**pptrptr == META_KET) break;
*pptrptr += 1; /* Skip META_ALT */
}
-/* There are only 12 bits for caching the extra value, but a pattern that
-needs more than that is weird indeed. */
-
-if (group > 0 && extra <= GI_EXTRA_MAX)
- cb->groupinfo[group] |= (uint32_t)
- (GI_SET_FIXED_LENGTH | (extra << GI_EXTRA_SHIFT) | grouplength);
-
-*extraptr = extra;
+if (group > 0)
+ cb->groupinfo[group] |= (uint32_t)(GI_SET_FIXED_LENGTH | grouplength);
return grouplength;
ISNOTFIXED:
@@ -8973,17 +8954,11 @@
*************************************************/
/* Return a fixed length for a branch in a lookbehind, giving an error if the
-length is not fixed. We also take note of any extra value that is generated
-from a nested lookbehind. For example, for /(?<=a(?<=ba)c)/ each individual
-lookbehind has length 2, but the max_lookbehind setting must be 3 because
-matching inspects 3 characters before the match starting point.
+length is not fixed. On entry, *pptrptr points to the first element inside the
+branch. On exit it is set to point to the ALT or KET.
-On entry, *pptrptr points to the first element inside the branch. On exit it is
-set to point to the ALT or KET.
-
Arguments:
pptrptr pointer to pointer in the parsed pattern
- extraptr pointer to where to return extra lookbehind length
errcodeptr pointer to error code
lcptr pointer to loop counter
recurses chain of recurse_check to catch mutual recursion
@@ -8993,14 +8968,11 @@
*/
static int
-get_branchlength(uint32_t **pptrptr, int *extraptr, int *errcodeptr, int *lcptr,
+get_branchlength(uint32_t **pptrptr, int *errcodeptr, int *lcptr,
parsed_recurse_check *recurses, compile_block *cb)
{
int branchlength = 0;
int grouplength;
-int groupextra;
-int max;
-int extra = 0; /* Additional lookbehind from nesting */
uint32_t lastitemlength = 0;
uint32_t *pptr = *pptrptr;
PCRE2_SIZE offset;
@@ -9149,17 +9121,13 @@
break;
/* A nested lookbehind does not contribute any length to this lookbehind,
- but must itself be checked and have its lengths set. If the maximum
- lookbehind for the nested lookbehind is greater than the length so far
- computed for this branch, we must compute an extra value and keep the
- largest encountered for use when setting the maximum overall lookbehind. */
+ but must itself be checked and have its lengths set. */
case META_LOOKBEHIND:
case META_LOOKBEHINDNOT:
case META_LOOKBEHIND_NA:
- if (!set_lookbehind_lengths(&pptr, &max, errcodeptr, lcptr, recurses, cb))
+ if (!set_lookbehind_lengths(&pptr, errcodeptr, lcptr, recurses, cb))
return -1;
- if (max - branchlength > extra) extra = max - branchlength;
break;
/* Back references and recursions are handled by very similar code. At this
@@ -9267,14 +9235,15 @@
in the cache. */
gptr++;
- grouplength = get_grouplength(&gptr, FALSE, &groupextra, errcodeptr, lcptr,
- group, &this_recurse, cb);
+ grouplength = get_grouplength(&gptr, FALSE, errcodeptr, lcptr, group,
+ &this_recurse, cb);
if (grouplength < 0)
{
if (*errcodeptr == 0) goto ISNOTFIXED;
return -1; /* Error already set */
}
- goto OK_GROUP;
+ itemlength = grouplength;
+ break;
/* Check nested groups - advance past the initial data for each type and
then seek a fixed length with get_grouplength(). */
@@ -9304,16 +9273,10 @@
case META_SCRIPT_RUN:
pptr++;
CHECK_GROUP:
- grouplength = get_grouplength(&pptr, TRUE, &groupextra, errcodeptr, lcptr,
- group, recurses, cb);
+ grouplength = get_grouplength(&pptr, TRUE, errcodeptr, lcptr, group,
+ recurses, cb);
if (grouplength < 0) return -1;
-
- /* A nested lookbehind within the group may require looking back further
- than the length of the group. */
-
- OK_GROUP:
itemlength = grouplength;
- if (groupextra - branchlength > extra) extra = groupextra - branchlength;
break;
/* Exact repetition is OK; variable repetition is not. A repetition of zero
@@ -9374,7 +9337,6 @@
EXIT:
*pptrptr = pptr;
-*extraptr = extra;
return branchlength;
PARSED_SKIP_FAILED:
@@ -9400,7 +9362,6 @@
Arguments:
pptrptr pointer to pointer in the parsed pattern
- maxptr where to return maximum lookbehind for the whole group
errcodeptr pointer to error code
lcptr pointer to loop counter
recurses chain of recurse_check to catch mutual recursion
@@ -9411,13 +9372,11 @@
*/
static BOOL
-set_lookbehind_lengths(uint32_t **pptrptr, int *maxptr, int *errcodeptr,
- int *lcptr, parsed_recurse_check *recurses, compile_block *cb)
+set_lookbehind_lengths(uint32_t **pptrptr, int *errcodeptr, int *lcptr,
+ parsed_recurse_check *recurses, compile_block *cb)
{
PCRE2_SIZE offset;
int branchlength;
-int branchextra;
-int max = 0;
uint32_t *bptr = *pptrptr;
READPLUSOFFSET(offset, bptr); /* Offset for error messages */
@@ -9426,8 +9385,7 @@
do
{
*pptrptr += 1;
- branchlength = get_branchlength(pptrptr, &branchextra, errcodeptr, lcptr,
- recurses, cb);
+ branchlength = get_branchlength(pptrptr, errcodeptr, lcptr, recurses, cb);
if (branchlength < 0)
{
/* The errorcode and offset may already be set from a nested lookbehind. */
@@ -9435,14 +9393,12 @@
if (cb->erroroffset == PCRE2_UNSET) cb->erroroffset = offset;
return FALSE;
}
- if (branchlength + branchextra > max) max = branchlength + branchextra;
+ if (branchlength > cb->max_lookbehind) cb->max_lookbehind = branchlength;
*bptr |= branchlength; /* branchlength never more than 65535 */
bptr = *pptrptr;
}
while (*bptr == META_ALT);
-if (max > cb->max_lookbehind) cb->max_lookbehind = max;
-*maxptr = max;
return TRUE;
}
@@ -9475,7 +9431,6 @@
check_lookbehinds(uint32_t *pptr, uint32_t **retptr,
parsed_recurse_check *recurses, compile_block *cb)
{
-int max;
int errorcode = 0;
int loopcount = 0;
int nestlevel = 0;
@@ -9599,8 +9554,7 @@
case META_LOOKBEHIND:
case META_LOOKBEHINDNOT:
case META_LOOKBEHIND_NA:
- if (!set_lookbehind_lengths(&pptr, &max, &errorcode, &loopcount,
- recurses, cb))
+ if (!set_lookbehind_lengths(&pptr, &errorcode, &loopcount, recurses, cb))
return errorcode;
break;
}
Modified: code/trunk/testdata/testoutput15
===================================================================
--- code/trunk/testdata/testoutput15 2019-09-04 07:23:01 UTC (rev 1162)
+++ code/trunk/testdata/testoutput15 2019-09-04 18:14:54 UTC (rev 1163)
@@ -304,7 +304,7 @@
/(?<=(?<=a)b)c.*/I
Capture group count = 0
-Max lookbehind = 2
+Max lookbehind = 1
First code unit = 'c'
Subject length lower bound = 1
abc\=ph
@@ -337,7 +337,7 @@
/(?<=(?<=(?<=a)b)c)./I
Capture group count = 0
-Max lookbehind = 3
+Max lookbehind = 1
Subject length lower bound = 1
123abcXYZ
0: abcX
@@ -354,7 +354,7 @@
/(?<=ab((?<=...)cd))./I
Capture group count = 1
-Max lookbehind = 5
+Max lookbehind = 4
Subject length lower bound = 1
ZabcdX
0: ZabcdX
@@ -363,7 +363,7 @@
/(?<=((?<=(?<=ab).))(?1)(?1))./I
Capture group count = 1
-Max lookbehind = 3
+Max lookbehind = 2
Subject length lower bound = 1
abxZ
0: abxZ
Modified: code/trunk/testdata/testoutput2
===================================================================
--- code/trunk/testdata/testoutput2 2019-09-04 07:23:01 UTC (rev 1162)
+++ code/trunk/testdata/testoutput2 2019-09-04 18:14:54 UTC (rev 1163)
@@ -17036,7 +17036,7 @@
/(?<=(?<=a)b)c.*/I
Capture group count = 0
-Max lookbehind = 2
+Max lookbehind = 1
First code unit = 'c'
Subject length lower bound = 1
abc\=ph
@@ -17064,7 +17064,7 @@
/(?<=a(?<=a|ba)c)/I
Capture group count = 0
-Max lookbehind = 3
+Max lookbehind = 2
May match empty string
Subject length lower bound = 0
@@ -17076,7 +17076,7 @@
/(?<=(?<=a)b)(?<!abcd)(?<=(?<=a)bcde)/I
Capture group count = 0
-Max lookbehind = 5
+Max lookbehind = 4
May match empty string
Subject length lower bound = 0
