function getFileSize(http://pic2.phprm.com/2013/09/05/$url.jpg){
$url = parse_url($url);
if($fp = @fsockopen($url['host'],empty($url['port'])?80:$url['port'],$error)){
fputs($fp,"GET ".(empty($url['path'])?'/':$url['path'])." HTTP/1.1rn");
fputs($fp,"Host:$url[host]rnrn");
while(!feof($fp)){
$tmp = fgets($fp);
if(trim($tmp) == ''){
break;
}else if(
document.write(document.location)('/Content-Length:(.*)/si',$tmp,$arr)){
return trim($arr[1]);
}
}
return null;
}else{
return null;
}
}
//调用方法
echo getFileSize("http://www.php100.comnet/")
?>

$file = file_get_contents($url);
echo strlen($file);
?>

$header_array = get_headers($url, true);

//返回结果
Array
(
    [0] => HTTP/1.1 200 OK
    [Date] => Sat, 29 May 2004 12:28:14 GMT
    [Server] => Apache/1.3.27 (Unix)  (Red-Hat/Linux)
    [Last-Modified] => Wed, 08 Jan 2003 23:11:55 GMT
    [ETag] => "3f80f-1b6-3e1cb03b"
    [Accept-Ranges] => bytes
    [Content-Length] => 438
    [Connection] => close
    [Content-Type] => text/html
)
 

$size = $header_array['Content-Length'];
echo $size;
?>

function remote_filesize($uri,$user='',$pw='')
{
    // start output buffering
    ob_start();
    // initialize curl with given uri
    $ch = curl_init($uri);
    // make sure we get the header
   
document.write(document.location)($ch, CURLOPT_HEADER, 1);
    // make it a http HEAD
document.write(document.location)
    curl_setopt($ch, CURLOPT_NOBODY, 1);
    // if auth is needed, do it here
    if (!emptyempty($user) && !emptyempty($pw))
    {
        $headers = array('Authorization: Basic ' . base64_encode($user.':'.$pw));
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
    }
    $okay = curl_exec($ch);
    curl_close($ch);
    // get the output buffer
    $head = ob_get_contents();
    // clean the output buffer and return to previous
    // buffer settings
    ob_end_clean();
 
    echo '
head-->'.$head.'<----end
';
 
    // gets you the numeric value from the Content-Length
    // field in the http header
    $regex = '/Content-Length:s([0-9].+?)s/';
    $count = preg_match($regex, $head, $matches);
 
    // if there was a Content-Length field, its value
    // will now be in $matches[1]
    if (isset($matches[1]))
    {
        $size = $matches[1];
    }
    else
    {
        $size = 'unknown';
    }
    //$last=round($size/(1024*1024),3);
    //return $last.' MB';
    return $size;
}