请教大胡子wpjam_get_post_first_image

function wpjam_get_post_first_image($post_content=\'\', $size=\'full\'){
if(!$post_content){
$the_post = get_post();
$post_content = $the_post->post_content;
}

preg_match_all( \'/class=[\\\'\"].*?wp-image-([d]*)[\\\'\"]/i\', $post_content, $matches );
if( $matches && isset($matches[1]) && isset($matches[1][0]) ){
$image_id = $matches[1][0];
if($image_url = wpjam_get_post_image_url($image_id, $size)){
return $image_url;
}
}

preg_match_all(\'|