Since PHP 4.2.0, PHP returns an appropriate error code
along with the file array. The error code can be found in the
['error'] segment of the file array that is
created during the file upload by PHP. In otherwords, the
error might be found in
$_FILES['userfile']['error'].
Value: 0; There is no error, the file uploaded
with success.
Value: 1; The uploaded file exceeds the
upload_max_filesize directive in php.ini.
Value: 2; The uploaded file exceeds the
MAX_FILE_SIZE directive that was specified
in the html form.
Value: 3; The uploaded file was only partially
uploaded.
Value: 4; No file was uploaded.
注: These became PHP constants in PHP 4.3.0