php9个超全局变量的用法详解（三）
今天要继续php9个超全局变量的系列，今天说一说$_FILE的用法.
首先呢，类似与$_POST等， $_FILES适用于上传文件类的input标签，$_FIFLES类似于一个二维数组，可以得到并保存客户端上传的文件的各种信息，具体如下：
$_FILES['myFile']['name'] 客户端文件的原名称。
$_FILES['myFile']['type'] 文件的 MIME 类型，需要浏览器提供该信息的支持，例如"image/gif"。
$_FILES['myFile']['size'] 已上传文件的大小，单位为字节。
$_FILES['myFile']['tmp_name'] 文件被上传后在服务端储存的临时文件名，一般是系统默认。可以在php.ini的upload_tmp_dir 指定，但 用 putenv() 函数设置是不起作用的。
$_FILES['myFile']['error'] 和该文件上传相关的错误代码。['error'] 是在 PHP 4.2.0 版本中增加的。下面是它的说明：(它们在PHP3.0以后成了常量)
所以，通过上面的这写变量便可以用于后台处理用户上传的文件了，例如只能上传图片类的，则可以通过$_FILES['myFile']['type']来限制，限制大小则可以通过$_FILES['myFile']['size'] 来指定，接下来，我以w3school上的例子来解释$_FILES的具体用法。
该demo主要实现的功能是上传图片类的文件并保存在服务器端的相关目录下。
html代码如下：
<html> <body> <form action="post.php" method="post" enctype="multipart/form-data"> <label for="file">Filename:</label> <input type="file" name="file" id="file"><br/> <input type="submit" name="submit" value="Submit"> </form> </body> </html>
代码很简单，只是定义了一个上传控件，注意这个name对应的值‘file’是$_FILES获得前台文件的依据，若后台获得文件类型写成$_FILES['myFile']['type']，说明前台的name对应的值一定要为'myFile',不然会报Invalid file的错误。最后看一下后台的代码：
<?php
$allowedExts = array("gif", "jpeg", "jpg", "png");
/*
* explode(separator,string,limit)
参数 描述
separator 必需。规定在哪里分割字符串。
string 必需。要分割的字符串。
limit 可选。规定所返回的数组元素的最大数目。
*/
$temp = explode(".", $_FILES["file"]["name"]);
//end() 函数将数组内部指针指向最后一个元素，并返回该元素的值（如果成功）。
$extension = end($temp);
if ((($_FILES["file"]["type"] == "image/gif")
($_FILES["file"]["type"] == "image/jpeg")
($_FILES["file"]["type"] == "image/jpg")
($_FILES["file"]["type"] == "image/pjpeg")
($_FILES["file"]["type"] == "image/x-png")
($_FILES["file"]["type"] == "image/png"))
&& ($_FILES["file"]["size"] < 200000)
/*
* in_array(value,array,type)
* in_array() 函数在数组中搜索给定的值。
* 如果给定的值 value 存在于数组 array 中则返回 true。如果第三个参数设置为 true，函数只有在元素存在于数组中且数据类型与给定值相同时才返回 true。
如果没有在数组中找到参数，函数返回 false。
注释：如果 value 参数是字符串，且 type 参数设置为 true，则搜索区分大小写。
*
* move_uploaded_file() 函数将上传的文件移动到新位置。
* move_uploaded_file(file,newloc)
* 本函数检查并确保由 file 指定的文件是合法的上传文件（即通过 PHP 的 HTTP POST 上传机制所上传的）。如果文件合法，则将其移动为由 newloc 指定的文件。*/
&& in_array($extension, $allowedExts))
{
if ($_FILES["file"]["error"] > 0)
{
echo "Return Code: " . $_FILES["file"]["error"] . "<br/>";
}
else
{
echo "Upload: " . $_FILES["file"]["name"] . "<br/>";
echo "Type: " . $_FILES["file"]["type"] . "<br/>";
echo "Size: " . ($_FILES["file"]["size"] / 1024) . " kB<br/>";
echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br/>";
if (file_exists("upload/" . $_FILES["file"]["name"]))
{
echo $_FILES["file"]["name"] . " already exists. ";
}
else
{
move_uploaded_file($_FILES["file"]["tmp_name"],
"upload/" . $_FILES["file"]["name"]);
echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
}
}
}
else
{
echo "Invalid file";
}
?>里面主要用到了explode(),end(),和in_array()三个主要函数，其用法我都做了注释解释，都很好理解，你看，用php实现上传一个文件是多么的简单，需要注意的一点是：文件被上传结束后，默认地被存储在了临时目录中，这个目录可以通过$_FILES['myFile']['tmp_name'] 来访问，这时您必须将它从临时目录中删除或移动到其它地方，如果没有，则会被删除。也就是不管是否上传成功，脚本执行完后临时目录里的文件肯定会被删除。所以本例当中用move_uploaded_files()函数将它复制到其它位置，此时，才算完成了上传文件过程。
最后，如果需要的话还是可以下载一下源码的，虽然很简单。
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