Regular Expression in C

Question

Hello,

Doing regex in C# or PHP is very easy for me now. However currently I have a need to use regex in C. And, I don't seem to understand the usage of regcomp or regexec fully. It's definitely because of my lack of experience in C.

Any help and examples would be much appreciated!

Answer 1

Use the PCRE library. Examples are included in the source, in the demo/ directory. Here's a direct link to pcredemo.c.

Answer 2

You need a library that provides it, and there are several to choose from. PCRE is one.

Answer 3

The gnu C library has a regex library

Answer 4

This may get you started, as you indicate regex(3) functions. Following is a trivial program matching its arguments. However, if you're relatively new to C, you'll want to go slowly with regex(3), as you'll be working with pointers and arrays and regmatch_t-supplied offsets and lions and tigers and bears. ;)

$ ./regexec '[[:digit:]]'   56789  alpha  "   "  foo12bar
matched: 56789
matched: foo12bar
$ ./regexec '[[:digit:]](foo'
error: Unmatched ( or \(
$ ./regexec '['
error: Invalid regular expression

... and the source:

#include <sys/types.h>
#include <regex.h>
#include <stdio.h>

int main(int argc, char **argv) {
  int r;
  regex_t reg;

  ++argv;  /* Danger! */

  if (r = regcomp(&reg, *argv, REG_NOSUB|REG_EXTENDED)) {
    char errbuf[1024];
    regerror(r, &reg, errbuf, sizeof(errbuf));
    printf("error: %s\n", errbuf);
    return 1;
  }

  for (++argv; *argv; ++argv) {
    if (regexec(&reg, *argv, 0, NULL, 0) == REG_NOMATCH)
      continue;
    printf("matched: %s\n", *argv);
  }

  return 0;
}

Answer 5

There's also libslack(str) - string module:

http://libslack.org/manpages/str.3.html