PHP文件上传效能 - 单文件上传

PHP文件上传功能 -- 单文件上传
这一节内容主要介绍PHP上传文件的单文件上传功能。

PHP主要通过POST方法来上传文件，文件上传之后存放在服务器的临时目录下（可查看PHP配置文件php.ini中的选项upload_tmp_dir）

接下来，我们来看一例子：

----------------------------------------------------------------------

    if(isset($_POST['submit'])){
        switch($_FILES['upload_file']['error']){
            case UPLOAD_ERR_INI_SIZE:
                echo "文件大小超过了服务器的限制";
                break;
            case UPLOAD_ERR_FORM_SIZE:
                echo "文件大小超过了浏览器的限制";
                break;
            case UPLOAD_ERR_PARTIAL:
                echo "只上传了部分文件";
                break;
            case UPLOAD_ERR_NO_FILE:
                echo "没有文件被上传";
                break;
            case UPLOAD_ERR_NO_TMP_DIR:
                echo "找不到临时文件夹";
                break;
            case UPLOAD_ERR_CANT_WRITE:
                echo "文件写入失败";
                break;
            case UPLOAD_ERR_OK:
                $upload_dir = './'.iconv("UTF-8","gb2312",$_FILES['upload_file']['name']);
                if(file_exists($upload_dir)){
                    echo '<script>alert(已经存在同名文件)</script>';
                }else{
                    if(move_uploaded_file($_FILES['upload_file']['tmp_name'],$upload_dir)){
                        echo '<script>alert(文件上传成功)</script>';
                    }else{
                        echo '<script>alert(文件移动失败)</script>';
                    }
                }
                break;
        }
    }

?>

---------------------------------------------------------------------

我们先分析一下代码：
1、我们看到代码中包含有$_FILES['upload_file']['error']之类的变量，那么这是什么意思呢？
$_FILES是一个全局二维数组，包含了上传文件的所有信息。这个数组有5个元素，分别描述了上传文件的属性：
$_FILES['upload_file']['name']        上传文件的名称
$_FILES['upload_file']['type']        上传文件的MIME类型
$_FILES['upload_file']['size']        上传文件的大小（单位：字节）
$_FILES['upload_file']['tmp_name']    上传文件的临时名称
$_FILES['upload_file']['error']        上传状态码

2、我们看到代码中包含有 UPLOAD_ERR_PARTIAL 之类的名称，那么这又是什么意思呢？
这些就是上传状态码：
UPLOAD_ERR_INI_SIZE        文件大小超过了服务器的限制，设置 php.ini 中的 upload_max_filesize
UPLOAD_ERR_FORM_SIZE        文件大小超过了浏览器的限制，设置 MAX_FILE_SIZE 隐藏表单域参数
UPLOAD_ERR_PARTIAL        文件只上传了一部分
UPLOAD_ERR_NO_FILE        上传表单中没有指定文件
UPLOAD_ERR_NO_TMP_DIR        找不到临时文件
UPLOAD_ERR_CANT_WRITE        文件写入失败
UPLOAD_ERR_OK            文件上传成功
代码执行效果：

3、代码中的move_uploaded_file（）函数有什么作用？
因为文件上传后会被存放在服务器的临时目录下，这时候就需要利用move_uploaded_file（）将其移动到指定位置上。

注意：若文件上传失败，可能是 php 配置文件中的某些参数没有设置合适，

例如File Uploads中的

; Whether to allow HTTP file uploads.
; http://php.net/file-uploads
file_uploads = On

; Temporary directory for HTTP uploaded files (will use system default if not
; specified).
; http://php.net/upload-tmp-dir
upload_tmp_dir = "\xampp\tmp"

; Maximum allowed size for uploaded files.
; http://php.net/upload-max-filesize
upload_max_filesize = 2M

; Maximum number of files that can be uploaded via a single request
max_file_uploads = 20

此外还有：

; Maximum size of POST data that PHP will accept.
; Its value may be 0 to disable the limit. It is ignored if POST data reading
; is disabled through enable_post_data_reading.
; http://php.net/post-max-size
post_max_size = 8M

; Maximum amount of memory a script may consume (128MB)
; http://php.net/memory-limit
memory_limit = 128M

; Maximum execution time of each script, in seconds
; http://php.net/max-execution-time
; Note: This directive is hardcoded to 0 for the CLI SAPI
max_execution_time = 30

; Maximum amount of time each script may spend parsing request data. It's a good
; idea to limit this time on productions servers in order to eliminate unexpectedly
; long running scripts.
; Note: This directive is hardcoded to -1 for the CLI SAPI
; Default Value: -1 (Unlimited)
; Development Value: 60 (60 seconds)
; Production Value: 60 (60 seconds)
; http://php.net/max-input-time
max_input_time = 60