Question

Hi I have this code below which is meant to check that the url entered is valid. however the program always fails on the first if statment.

    regex_t regex;
    int reti;
    char msgbuf[100];

/* Compile regular expression */
        reti = regcomp(&regex, "^^((([hH][tT][tT][pP][sS]?|[fF][tT][pP])\:\/\/)?([\w\.\-]+(\:[\w\.\&%\$\-]+)*@)?((([^\s\(\)\<\>\\\"\.\[\]\,@;:]+)(\.[^\s\(\)\<\>\\\"\.\[\]\,@;:]+)*(\.[a-zA-Z]{2,4}))|((([01]?\d{1,2}|2[0-4]\d|25[0-5])\.){3}([01]?\d{1,2}|2[0-4]\d|25[0-5])))(\b\:(6553[0-5]|655[0-2]\d|65[0-4]\d{2}|6[0-4]\d{3}|[1-5]\d{4}|[1-9]\d{0,3}|0)\b)?((\/[^\/][\w\.\,\?\'\\\/\+&%\$#\=~_\-@]*)*[^\.\,\?\"\'\(\)\[\]!;<>{}\s\x7F-\xFF])?)$", 0);
        if( reti ){ 
           fprintf(stderr, "Could not compile regex\n"); 
           exit(1);
        }

/* Execute regular expression */
    reti = regexec(&regex, str, 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);

What is the reason that is always executes the first if statement? Also is there a better way to check if the url is syntactically correct?

Answer 1

I believe you need to use the REG_EXTENDED flag. It would also help if you used regerror() to get a better error message.

Other than that, my advice to debug a regex that large is to cut parts out until it works, then slowly add them back, so you can see exactly where you went wrong.