extraire plusieurs sous chaine d'un string en C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <regex.h>
 
int main (void)
{
  int err;
  regex_t preg;
  const char *str="chaine sous chaine sous  chaine toto";
  const char *str_regex="(sous +chaine)";
 
 
  err = regcomp (&preg, str_regex, REG_EXTENDED);
  if (err == 0)
  {
    int match;
    size_t nmatch = 0;
    regmatch_t *pmatch = NULL;
    char *buffer;
 
    nmatch = preg.re_nsub;
    printf ("taille: %d\n", nmatch);
    pmatch = malloc (sizeof (*pmatch) * nmatch);
    if (!pmatch)
    {
      fprintf (stderr, "Memoire insuffisante\n");
      exit (1);
    }
    buffer = (char *) str;
    match = regexec (&preg, buffer, nmatch, pmatch, 0);
    while (match == 0)
    {
      char *str_found = NULL;
      size_t size ;
      int start, end;
      start = pmatch[0].rm_so;
      end = pmatch[0].rm_eo;
      size = end - start;
 
      str_found = malloc (sizeof (*str_found) * (size + 1));
      if (str_found)
      {
       	strncpy (str_found, &buffer[start], size);
       	str_found[size] = '\0';
	printf ("%s\n", str_found);
	free (str_found);
      }
      match = regexec (&preg, (buffer += end), nmatch, pmatch, 0);
    }
    regfree (&preg);
    free (pmatch);
  }
  return 0;
}