判断链接地址是否有效

public function gethttpcode($url){
        $ch = curl_init ();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_TIMEOUT, 2);
        curl_setopt($ch, CURLOPT_HEADER, FALSE);
        curl_setopt($ch, CURLOPT_NOBODY, FALSE);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
        curl_setopt($ch, CURLOPT_FOLLOWLOCATION, FALSE);
        curl_setopt($ch, CURLOPT_CUSTOMREQUEST, 'GET');
        curl_exec($ch);
        $httpcode=intval(curl_getinfo($ch,CURLINFO_HTTP_CODE)/100);
        if($httpcode==4 || $httpcode==5 || $httpcode==0){
            return false;
        }
        return true;
    }