检测上传的文件是否太大

这是我的上传表单：

<form action="uploads.php" method="post" enctype="multipart/form-data">
    <input name="fileupload" type="file" multiple>
    <button>Upload</button>
</form>

我的最大上传大小设置如下：

; Maximum allowed size for uploaded files.
upload_max_filesize = 5M

; Must be greater than or equal to upload_max_filesize
post_max_size = 5M

如果我上传大于5M的文件var_dump($_FILES)是空的。我可以这样做：

if($_FILES){
    echo "Upload done!";
}

$_FILES如果文件大于 5M，则不设置。但这有点奇怪。你会怎么做？

EDIT:

超过5M文件的var_dump：

array(0) {
}

文件

array(1) {
  ["fileupload"]=>
  array(5) {
    ["name"]=>
    string(13) "netzerk12.pdf"
    ["type"]=>
    string(15) "application/pdf"
    ["tmp_name"]=>
    string(22) "/tmp/uploads/phpWhm8M0"
    ["error"]=>
    int(0)
    ["size"]=>
    int(352361)
  }
}

你可以检查$_SERVER['CONTENT_LENGTH']:

// check that post_max_size has not been reached
// convert_to_bytes is the function turn `5M` to bytes because $_SERVER['CONTENT_LENGTH'] is in bytes.
if (isset($_SERVER['CONTENT_LENGTH']) 
    && (int) $_SERVER['CONTENT_LENGTH'] > convert_to_bytes(ini_get('post_max_size'))) 
{
  // ... with your logic
  throw new Exception('File too large!');
}