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($upload_dir)){
echo '';
}else{
if(move_uploaded_file($_FILES['upload_file']['tmp_name'],$upload_dir)){
echo '';
}else{
echo '';
}
}
break;
}
}
?>
---------------------------------------------------------------------
我们先分析一下代码：
1、我们看到代码中包含有$_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.com/file-uploads
file_uploads = On
; Temporary directory for HTTP uploaded files (will use system default if not
; specified).
; http://php.com/upload-tmp-dir
upload_tmp_dir = "\xampp\tmp"
; Maximum allowed size for uploaded files.
; http://php.com/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.com/post-max-size
post_max_size = 8M
; Maximum amount of memory a script may consume (128MB)
; http://php.com/memory-limit
memory_limit = 128M
; Maximum execution time of each script, in seconds
; http://php.com/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.com/max-input-time
max_input_time = 60
