regex.h question

MTK358 · 06-08-2010, 09:28 AM

Using the regex.h functions, how do you:

1) get the matched strings?

2) get the strings that matched sub-expressions?

paulsm4 · 06-08-2010, 11:53 AM

Try Googling for "C regex tutorial".

Here are a couple of hits:

http://cboard.cprogramming.com/c-pro...g-matches.html

http://wiki.hypexr.org/wikka.php?wakka=RegexExamples

http://www.peope.net/old/regex.html

Here's a complete example (no, I haven't actually tried it

):

Code:

#include <stdio.h>
#include <stdlib.h>
#include <regex.h>

char *regexp (char *string, char *patrn, int *begin, int *end) {     
        int i, w=0, len;                  
        char *word = NULL;
        regex_t rgT;
        regmatch_t match;
        regcomp(&rgT,patrn,REG_EXTENDED);
        if ((regexec(&rgT,string,1,&match,0)) == 0) {
                *begin = (int)match.rm_so;
                *end = (int)match.rm_eo;
                len = *end-*begin;
                word=malloc(len+1);
                for (i=*begin; i<*end; i++) {
                        word[w] = string[i];
                        w++; }
                word[w]=0;
        }
        regfree(&rgT);
        return word;
}


int main() {
	int b,e;
	char *match=regexp("this and7 that","[a-z]+[0-9]",&b,&e);
	printf("->%s<-\n(b=%d e=%d)\n",match,b,e);
	return 0;
}

MTK358 · 06-08-2010, 03:43 PM

I made a simple grep-like program and it works:

Code:

#include <stdio.h>
#include <regex.h>

int main(int argc, char **argv)
{
	if (argc != 2)
	{
		fprintf(stderr, "Usage: %s [ERE]\n", argv[0]);
		return 1;
	}
	
	regex_t re;
	regmatch_t match;
	int status;
	status = regcomp(&re, argv[1], REG_EXTENDED);
	
	if (status != 0)
	{
		fprintf(stderr, "error: %s: invalid ERE\n", argv[1]);
		return 2;
	}
	
	char line[512];
	while (fgets(line, 512, stdin))
	{
		status = regexec(&re, line, 1, &match, 0);
		if (status == 0)
		{
			printf("%d-%d: %s\n", match.rm_so, match.rm_eo, line);
		}
	}
	
	return 0;
}

// EOF

But how do I get the substrings matched by sub-expressions contained in "()"s?

And what about multiple matches in the same string, not just the first one?

paulsm4 · 06-08-2010, 04:09 PM

Use Perl

?

Sergei Steshenko · 06-08-2010, 04:10 PM

Quote:

Originally Posted by MTK358

...
But how do I get the substrings matched by sub-expressions contained in "()"s?

And what about multiple matches in the same string, not just the first one?

And why do you think

man 3 regex

does not provide the needed info ?