From:	mauch AT uni-duisburg DOT de (Michael Mauch)
Newsgroups:	comp.os.msdos.djgpp
Subject:	DJGPP regex - how does it work?
Date:	Fri, 05 Sep 1997 00:34:28 +0200
Organization:	Home, sweet home (via Gesamthochschule Duisburg)
Lines:	124
Message-ID:	<5und1g$l9o$2@news-hrz.uni-duisburg.de>
NNTP-Posting-Host:	ppp69.uni-duisburg.de
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Hi!

I tried to use the functions regcomp() and regexec() from DJGPP's
regex.h, but obviously I'm plain too dumb to get these things to work.

Does anybody have a simple, working example how to use regex.h?

I include my test program below. It always prints "Matching", even if I
match the RE "a" against the string "b". If I supply an invalid regular
expression such as "a[" - then regcomp() works as expected (i.e. it
fails) and regerror() tells me where the problem is.

BTW: Searching for an example program using "regex.h", I found the file
DJGPP\TESTS\LIBC\POSIX\REGEX\r1.c which seems to be rather
incomplete/broken - is this only on my machine or is there another
secret behind it? On my machine it looks like this:

// DJGPP\TESTS\LIBC\POSIX\REGEX\r1.c
#include <stdio.h>
#include <regex.h>

int
main(int argc, char **argv)
{
  rexec_
  regcomp("a.*x"
}


Now, following is my test program. I'd be grateful if somebody could
look through it and tell me where I went wrong.

Thanks in advance...
		Michael

// RegTest.c
#include <stdio.h>
#include <stdlib.h>

#include <stdarg.h>

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


int Usage(void)
{
  fprintf(stderr,"\nUsage: regtest expr string\n\n"
                 "Returns 0 if string matches the extended RE expr, "
                 "1 otherwise, "
                 "2 for errors.\n"
         );
  return 2;
}


void Error(int exit_code,char* format,...)
{
  va_list arg;
  va_start(arg, format);

  fprintf(stderr,"\nError: ");
  vfprintf(stderr, format, arg);
  fprintf(stderr,"\n");

  va_end(arg);
  exit(exit_code);
}

char* RegError(int r,regex_t* preg)
/*
   Returns the human-readable regex error string
   in a dynamically allocated array.
   The caller must free() this array.
*/
{
  char* pBuf;
  size_t BufLen;

  BufLen = regerror(r,preg,NULL,0);
  pBuf = (char*)malloc(BufLen);
  regerror(r,preg,pBuf,BufLen);

  return pBuf;
}

int main(int argc,char* argv[])
{
  char* strRegex, *strString;
  int r;
  regex_t regex;
  int cFlags = REG_NOSUB | REG_EXTENDED;  // flags for regcomp()
  int eFlags = 0;                         // flags for regexec()
  regmatch_t pMatch[1];

  if(argc<3)
    return Usage();

  strRegex = argv[1];
  strString = argv[2];

  r = regcomp(&regex,strRegex,cFlags);
  if(r)
    Error(2,"regcomp() says: %s\n",RegError(r,&regex));

  r = regexec(&regex,strRegex,1,pMatch,eFlags | REG_TRACE);
  // The following line didn't work as well:
  // r = regexec(&regex,strRegex,0,NULL,eFlags);
  if(!r)
  {
    printf("Matching.\n");
    return 0;   // found
  }
  else if(REG_NOMATCH == r)
  {
    printf("No match.\n");
    return 1;   // not found
  }
  else
    Error(2,"regexec() says: %s\n",RegError(r,&regex));

  return 2;
}

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