Question

I’m trying to verify that a URL input by a user is in the required format, in this case I am trying to remove the http:// if it is present but I am encountering some very strange problems…

if I feed the function “www.google.com” or “http://www.google.com” everything goes as expected! However if I feed it something that is not a valid URL (e.g. potato) it returns gibberish located in memory…

Why this is not necissarily a problem it definitely is NOT expected program behavior, and I have no idea why it’s behaving this way…

Enter URL: potato

Error! Could not resolve ip address for host: ╪☻ï*** Process returned 1 ***
Press any key to continue...

Here is the function in question:

char *bldurl(const char *url)
{
    char *nurl;
    int ch = 0, i = 0;

    if(chksbstr(url, "http://") < 0)
    {
        if(!(nurl = malloc(strln(url) + 8)))
        {
            printf("\nError! Memory allocation failed while appending URL!");
            return 0x00;
        }
        nurl[ch] = 'h';
        nurl[++ch] = 't';
        nurl[++ch] = 't';
        nurl[++ch] = 'p';
        nurl[++ch] = ':';
        nurl[++ch] = '/';
        nurl[++ch] = '/';
        for(++ch; i <= strln(url); ch++, i++) nurl[ch] = url[i];
        nurl[--ch] = 0x00; 
    }
    else
    {
        if(!(nurl = malloc(strln(url) + 1)))
        {
            printf("\nError! Memory allocation failed while appending URL!");
            return 0x00;
        }
        for(i = 0; i <= strln(url); i++) nurl[i] = url[i];
        nurl[i + 1] = 0x00;
    }
    return nurl;
}

And here is the portion of my code that returns that particular error message:

    if(!(hostip = gethostbyname(hostname)))
    {
        free(hostname);
        free(url);
        printf("\nError! Could not resolve ip address for host: %s", hostname);
        WSACleanup();
        return 0x00;
    }

hostname in the above code is the return value from the for mentioned function.

I’m really not sure what to think.

Answer 1

You are calling a ‘free’ on hostname and then trying to print it out; of course it will be something unreadable! You should really print it then free it, I guess.