POSIX regex alternate not working

Question

I'm using | for alternatives but it's not working. Am I doing something wrong?

Thanks!

The following code always return No match:

#include <sys/types.h>
#include <regex.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>

int main(int argc, char *argv[]){
        regex_t regex;
        int reti;
        char msgbuf[100];

/* Compile regular expression */
        reti = regcomp(&regex, "ab(c|d)", 0);
        if( reti ){ fprintf(stderr, "Could not compile regex\n"); exit(1); }

/* Execute regular expression */
        reti = regexec(&regex, "abd", 0, NULL, 0);
        if( !reti ){
                puts("Match");
        }
        else if( reti == REG_NOMATCH ){
                puts("No match");
        }
        else{
                regerror(reti, &regex, msgbuf, sizeof(msgbuf));
                fprintf(stderr, "Regex match failed: %s\n", msgbuf);
                exit(1);
        }

/* Free compiled regular expression if you want to use the regex_t again */
    regfree(&regex);

        return 0;

}

Answer 1

As the POSIX manual says, you need to set the flags argument to allow extended regular expressions.

   REG_EXTENDED
          Use POSIX Extended Regular Expression syntax  when  interpreting
          regex.   If  not  set,  POSIX Basic Regular Expression syntax is
          used.