about regular expression

below code for searching relative path for resource in html text,but when using regcomp method to complie the regular expression,a error is printed:Invalid preceding regular expression;I dont know if <regex.h> does not support (?! xxx ) or something else make the error

Code:

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

//for searching relative path
#define SRC_RELATIVE "src\\s*=\\s*\"?(?!http|/|\"http|\"/)\\S+\\.%s\"?"

//for test
char *s= " src=aaa.gif src=\"aaa.gif\" \
Src = /aaa/aaa.gif src = \"/aaa/aaa.gif\" \
src = http://www.site.com/aaa.gif src = \"http://www.site.com/aaa.gif\" ";


char *get_regerror (int errcode, regex_t *compiled){
      size_t length = regerror (errcode, compiled, NULL, 0);
      char *buffer = malloc(length);
      regerror (errcode, compiled, buffer, length);
      return buffer;
}

void doit(char *src,char *reg,char *restype){
      char line[100];
      char *c = src;
      char result[100];
      regex_t r;
      regmatch_t match;
      int i;

      bzero(line,sizeof(line));
      snprintf(line,sizeof(line),reg,restype);

      if((i = regcomp(&r,line,REG_EXTENDED | REG_ICASE)) != 0){
            fprintf(stderr,"%s\n",get_regerror(i,&r));
            exit(1);
      }
      while((i = regexec(&r,c,1,&match,0)) == 0) {
            bzero(result,sizeof(result));
            int eo = (int)match.rm_eo;
            int so = (int)match.rm_so;
            memcpy(result,c + so,eo - so);
            printf("%s\n",result);
            c += match.rm_eo;//for another match
      }
      regfree(&r);
}

int main(){
      printf("relative path:\n");
      doit(s,SRC_RELATIVE,"gif");

      return 0;
}

REG_BADRPT is your return code - I assume.

The leading ? character doesn't have a preceding regular expression -
(?!http|/|\"http|\"/) the leading "?" is invalid - this version of the regex engine does not support it.