Author: ph10 Date: To: Jayaprakasam, Kannan CC: pcre-dev@exim.org Subject: Re: [pcre-dev] Extracting non existant pattern name gives 0 length
instead of PCRE_ERROR_NOSUBSTRING
On Wed, 18 Sep 2013, Jayaprakasam, Kannan wrote:
> When I match a subject that doesn't contain the return value, and I call
> pcre_get_named_substring(m_regexSPCall, sqlStmtUtf8, ovector, matchedCount, "retPort");
> lt doesn't return PCRE_ERROR_NOSUBSTRING but 0. Why does this happen?
This extract from the pcreapi man page explains the reason:
When any of these functions encounter a substring that is unset, which
can happen when capturing subpattern number n+1 matches some part of
the subject, but subpattern n has not been used at all, they return an
empty string. This can be distinguished from a genuine zero-length
substring by inspecting the appropriate offset in ovector, which is
negative for unset substrings.
The error PCRE_ERROR_NOSUBSTRING is given only for non-existent substrings.
