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Mail Archives: djgpp/2002/04/11/12:30:15

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From: "Goh, Yong Kwang" <gohyongkwang AT hotmail DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Allocate memory for pmatch[] prior to calling regexec()?
Date: Thu, 11 Apr 2002 16:51:10 +0800
Organization: Singapore Telecommunications Ltd
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

The prototype for regexec() looks like this:

int regexec(const regex_t *preg, const char *string, size_t nmatch,
regmatch_t pmatch[], int eflags);

So prior to calling regexec(), do we have to allocate memory for the
pmatch[] array of regmatch_t structures or it'll be dynamically allocated by
regexec() itself as it finds sub-expressions matches, conforming to the
compiled regex, in the string?

If we have to allocate memory for pmatch[], how do we know how many
sub-expressions there are in the regex, assuming the regex is only known
when the program is run and is determined by user's input, in order to
ensure sufficient number of regmatch_t structures to hold the sub-expression

Also, one thing that I cannot understand is that that size_t nmatch is
supposed to hold the number of matches (sub-expressions) it could find in
the string. But the fact is that it's passed by value (and not as pointer)
into regexec() and it couldn't possibly be updated by regexec() as it finds
matches, hence nmatch has to be of a known value before regexec starts. In
another word, the size of pmatch[] is already fixed and memory has already
been allocated for pmatch[] prior to calling regexec.

Could anyone care to enlighten me on the use of regexec()? Thanks.
Yong-Kwang Goh
gohyongkwang AT hotmail DOT com

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