PHP gets all links in the specified URL page

    //获取指定URL页面中所有链接
    function get_url_href($url){
        $html = file_get_contents($url);
        $dom = new DOMDocument();
        @$dom->loadHTML($html);
        $xpath = new DOMXPath($dom);
        $hrefs = $xpath->evaluate('/html/body//a');
        for($i=0;$i<$hrefs->length;$i++){
            $href = $hrefs->item($i);
            $url = $href->getAttribute('href');
            if(substr($url,0,4) == 'http') echo $url.'';
        }
    }

PHP, URl