pcre match empty string

#include <stdio.h>
#include <string.h>
#include <pcre.h>
#define OVECCOUNT 30    /* should be a multiple of 3 */
int main(int argc, char **argv)
{
  pcre *blankline,*re;
  const char *error;
  int erroffset;
  int ovector[OVECCOUNT];
  FILE *infile;
  char buf[BUFSIZ];
  char blank[] = "^\\s*$";
  if (argc != 2)
    {
      printf("Filename required\n");
      return 1;
    }
  blankline = pcre_compile(blank,PCRE_CASELESS,&error,&erroffset,NULL);
  if (!(infile = fopen(argv[1], "r"))) {
        printf("Could not open input file");
        exit(1);
  }
    while (fgets(buf, sizeof (buf), infile)) {
      int n= strlen(buf);
      buf[n - 1] = 0;
      puts(buf);
      rc = pcre_exec( blankline, NULL, buf, n, 0, 0, ovector, OVECCOUNT);
      if (rc > 0){
    break;
      }
    }
    return(0);
}