php获取远程文件大小

/* 
**功能:获取远程文件的大小,返回值的单位是:字节 
*/ 
function get_filesize($url){ 
  if(!isset($url)||trim($url)==''){ 
    return ''; 
  } 
  ob_start(); 
  $ch=curl_init($url); 
  curl_setopt($ch,curlopt_header,1); 
  curl_setopt($ch,curlopt_nobody,1); 
  $okay=curl_exec($ch); 
  curl_close($ch); 
  $head=ob_get_contents(); 
  ob_end_clean(); 
  $regex='/content-length:s([0-9].+?)s/'; 
  $count=preg_match($regex,$head,$matches); 
  return isset($matches[1])&&is_numeric($matches[1])?$matches[1]:''; 
}