UPLOAD_ERR_OK
Value: 0; There is no error, the file uploaded with success.
其值为 0，没有错误发生，文件上传成功。
UPLOAD_ERR_INI_SIZE
Value: 1; The uploaded file exceeds theupload_max_filesizedirective in php.ini.
其值为 1，上传的文件超过了php.ini中upload_max_filesize选项限制的值。
UPLOAD_ERR_FORM_SIZE
Value: 2; The uploaded file exceeds the MAX_FILE_SIZE directive that was specified in the HTML form.
其值为 2，上传文件的大小超过了 HTML 表单中 MAX_FILE_SIZE 选项指定的值。
UPLOAD_ERR_PARTIAL
Value: 3; The uploaded file was only partially uploaded.
其值为 3，文件只有部分被上传。