How to upload files and replace them in php

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The following is the form Submit the change.php file code and take a look at what is in this file:

<?php
header("content-type:text/html;charset=utf-8");
 
/**
* @param string $oldfile 需要更换的文件名（包含具体路径名）
*/
function changeFile($oldfile){
$newfile = $_FILES[&#39;file&#39;][&#39;name&#39;];//获取上传文件名
$fileclass = substr(strrchr($newfile, &#39;.&#39;), 1);//获取上传文件扩展名,做判断用
$type = array("jpg", "gif", "bmp", "jpeg", "png");//设置允许上传文件的类型
if(in_array(strtolower($fileclass), $type)){
if(file_exists($oldfile)){
unlink($oldfile);
}
if(is_uploaded_file($_FILES[&#39;file&#39;][&#39;tmp_name&#39;])){//必须通过 PHP 的 HTTP POST 上传机制所上传的
if(move_uploaded_file($_FILES[&#39;file&#39;][&#39;tmp_name&#39;], $oldfile)){
//输出图片预览
echo "<center>您的文件已经上传完毕 上传图片预览: </center><br><center><img src=&#39;$oldfile&#39;></center>";
}
}else{
echo "<center>上传失败，文件大于2M，请重新上传！</center>";
}
}else{
$text = implode(",", $type);
echo "<center>您只能上传以下类型文件：", $text, "</center><br>";
// echo "<script>alert(&#39;您只能上传以下类型文件：$text&#39;)</script>";
}
}
changeFile("./files/1.png");

You may be a little dizzy when you first read this~~, but if you look at it slowly, you will find that this thing is actually SO EASY!! Let’s talk about it first! Based on the following principle, this program takes uploading pictures as an example. It first determines whether the file type is an image format. If so, uploads the file, then uploads the file to and replaces the specified file. If the upload is successful, a preview of the uploaded picture will be output. Here are some functions in the program Let me give you some explanations. Let’s look at substr(strrchr($newfile, '.'), 1) first. What is the function of strrchar()? Let me give you an example. For example, for a picture file pic.jpg, we use strrchar( ) processing, strrchr(pic.jpg,'.'), it will return .jpg, do you understand? This function returns the string after the last position of the specified character in the string. With substr() we can get to jpg, so that we can get the suffix name of the file to determine whether the uploaded file conforms to the specified format. This program puts the specified format in an array, which can be added as needed during actual use.

Next, We call the function to determine the file type and convert it into lowercase strtolower($_FILES['file']['name']). There is a very key thing here $_FILES. This is a super global array that saves the required The processed form data can also be accessed directly if register_globals is turned on, but this is unsafe. Look at the upload interface just now . According to this form name, we can get a lot of information:

$_FILES['file']['name'] -- Get the file name

$_FILES['file']['tmp_name']--Get the temporary storage location

$_FILES['file']['size']--Get File size

$_FILES['file']['type']--Get the file MIME type

With this information, you can easily determine the file information. Isn't it very convenient? Next, there are some functions that need to be understood, file_exists()--determine whether the specified directory exists. If it does not exist, of course we cannot upload it (it seems like nonsense!), is_uploaded_file--determine whether the file has been uploaded through HTTP POST, move_uploaded_file--will upload The file is moved to the specified directory. If the upload is successful, we will output the preview, otherwise the output upload will fail...

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