Question

I am using Dev-c++ IDE to compile my C (WIN32 API) programs.

I am using regex lirary provided by http://gnuwin32.sourceforge.net/packages/regex.htm

I am using this documentation for reference and the same has been provided from the above site… http://pubs.opengroup.org/onlinepubs/009695399/functions/regcomp.html

Following is the Code:

#include <cstdlib>
#include <iostream>
#include <sys/types.h>
#include <regex.h>
#include <conio.h>
#include <stdio.h>

using namespace std;

int main(int argc, char *argv[])
{
    int a;
    regex_t re;
    char str[128] = "onces sam lived with samle to win samile hehe sam hoho sam\0";
    regmatch_t pm;

    a = regcomp(&re,"sam", 0);
    if(a!=0)
    {
        puts("Invalid Regex");
        getch();
        return 0;
    }
    
    a = regexec(&re, &str[0], 1, &pm, REG_EXTENDED);    
    printf("\n first match at %d",pm.rm_eo);        
    
    int cnt = 0;
    
    while(a==0)
    {
        a = regexec(&re, &str[0] + pm.rm_eo, 1, &pm, 0);

        printf("\n next match %d",pm.rm_eo);        
        
        cnt++;        
        if(cnt>6)break;
    }
    
    getch();  
    return EXIT_SUCCESS;
}

The while loop goes infinite displaying the first and second end position of the matching string and not going further.

I have used the cnt variable to check for 6 turns and then i am breaking the loop to stop the infinite run.

The Output is:

first match at 9

next match 15

next match 9

next match 15

next match 9

next match 15

What am i missing here?

Answer 1

Try this instead:

int cnt = 0;
int offset = 0;
a = regexec(&re, &str[0], 1, &pm, REG_EXTENDED);
while(a==0) {
    printf("\n %s match at %d", offset ? "next" : "first", offset+pm.rm_so);
    offset += pm.rm_eo;
    cnt++;
    a = regexec(&re, &str[0] + offset, 1, &pm, 0);
}

You were not actually stepping through your string, which was what caused the unending loop.