regex - PHP - Add link to a URL in a string

Question

I have a function that will add the <a href> tag before a link and </a> after the link. However, it breaks for some webpages. How would you improve this function? Thanks!

function processString($s) 
{
    // check if there is a link

    if(preg_match("/http:///",$s))
    {
        print preg_match("/http:///",$s);


        $startUrl =  stripos($s,"http://");

        // if the link is in between text
        if(stripos($s," ",$startUrl)){
            $endUrl = stripos($s," ",$startUrl);
        }
        // if link is at the end of string
        else {$endUrl = strlen($s);}

        $beforeUrl = substr($s,0,$startUrl);
        $url = substr($s,$startUrl,$endUrl-$startUrl);
        $afterUrl = substr($s,$endUrl);

        $newString = $beforeUrl."<a href="$url">".$url."</a>".$afterUrl;

        return $newString;
    }

    return $s;
}

Answer 1

function processString($s) {
    return preg_replace('/https?://[w-.!~#?&=+*'"(),/]+/','<a href="$0">$0</a>',$s);
}