C Regex multiple matches and groups example

match.c

# gcc -Wall -o match match.c && ./match
#


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


int main ()
{
  char * source = "___ abc123def ___ ghi456 ___";
  char * regexString = "[a-z]*([0-9]+)([a-z]*)";
  size_t maxMatches = 2;
  size_t maxGroups = 3;
  
  regex_t regexCompiled;
  regmatch_t groupArray[maxGroups];
  unsigned int m;
  char * cursor;
  char * cursorCopy = calloc(1,sizeof(char));
 
  if (regcomp(&regexCompiled, regexString, REG_EXTENDED))
    {
      printf("Could not compile regular expression.\n");
      return 1;
    };

  m = 0;
  cursor = source;
  for (m = 0; m < maxMatches; m ++)
    {
      if (regexec(&regexCompiled, cursor, maxGroups, groupArray, 0))
        break;  // No more matches

      unsigned int g = 0;
      unsigned int offset = 0;
      for (g = 0; g < maxGroups; g++)
        {
          if (groupArray[g].rm_so == (size_t)-1)
            break;  // No more groups

          if (g == 0)
            offset = groupArray[g].rm_eo;

          cursorCopy = realloc(cursorCopy,strlen(cursor) + 1);
          strcpy(cursorCopy, cursor);
          cursorCopy[groupArray[g].rm_eo] = 0;
          printf("Match %u, Group %u: [%2u-%2u]: %s\n",
                 m, g, groupArray[g].rm_so, groupArray[g].rm_eo,
                 cursorCopy + groupArray[g].rm_so);
        }
      cursor += offset;
    }

  regfree(&regexCompiled);
  free(cursorCopy);
  return 0;
}