0 - UPLOAD_ERR_OK 文件成功上传
1 - UPLOAD_ERR_INI_SIZE 超过php.ini里最大上传大小
2 - UPLOAD_ERR_FORM_SIZE 超过form表单最大上传大小
3 - UPLOAD_ERR_PARTIAL 文件没有完整上传
4 - UPLOAD_ERR_NO_FILE 没有上传文件
5 - UPLOAD_ERROR_E As expliained by @Progman, removed in rev. 81792
6 - UPLOAD_ERR_NO_TMP_DIR 找不到临时文件夹
7 - UPLOAD_ERR_CANT_WRITE 磁盘不可写
8 - UPLOAD_ERR_EXTENSION File upload stopped by extension