How to upload and replace images with PHP?-PHP Problem-php.cn

How to upload and replace images with PHP?

coldplay.xixi

Release： 2023-03-03 09:30:01

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PHP method to upload and replace images: first create two files; then a hidden field is needed to limit the maximum length of the uploaded file; then first determine whether the file type is an image format, and if so, upload the file; finally Just upload the file to and replace the specified file.

How to upload and replace images with PHP?

PHP method to upload and replace images:

First create two files: change.html and change .php

change.html The form code of the file is as follows:

<html>
<head>
<title>change file example.</title>
<meta charset="UTF-8">
</head>
<body>
<form method="post" action="changefile.php" enctype="multipart/form-data">
<table border=0 cellspacing=0 cellpadding=0 align=center width="100%">
<tr>
<td width=55 height=20 align="center">
<input type="hidden" name="MAX_FILE_SIZE" value="2000000" />
文件：
</td>
<td>
<input name="file" type="file" />
<input type="submit" name="submit" value="submit" /> 
</td>
</tr>
</table>
</form>
</body>
</html>

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There are several things to pay attention to here, first look at this sentence

<form method="post" action="change.php" enctype="multipart/form-data">

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Here we use the POST method. Some browsers also support the PUT method. Of course, this requires modifying the script, which I do not recommend. enctype="multipart/form-data must be set in the form, so that the server knows that the uploaded file contains regular form information. Remember, this must be set.

In addition, it is also required A hidden field to limit the maximum length of uploaded files: <input type="hidden" name="MAX_FILE_SIZE" value="2000000">, where name must be set to MAX_FILE_SIZE , its value is the maximum length of the uploaded file, the unit is B, here I limit it to 2M.

Look at this sentence again:

<input name="file" type="file"   value="浏览" >

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type="file" explains the file type, such a The basic file upload interface is complete. Next, we will talk about how to use PHP to process uploaded files. In addition, the maximum length of uploaded files set in your php.ini may affect your actual upload. Please modify it according to the actual situation. In addition, PHP uploads are first uploaded to the temporary directory and then moved to the specified directory; the temporary directory can be modified as needed, or the default value can be used.

The following is the form submission change.php file code , let’s take a look at what this file contains:

<?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");

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You may be a little dizzy when you first read these~~, if you look at it slowly, you will find that this thing is actually SO EASY!!

Let’s talk 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’s make some explanations.

Let’s first look at

substr(strrchr($newfile, &#39;.&#39;), 1)

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strrchar()What is the function? Let me give you an example, such as a picture file pic.jpg. We use strrchar() to process, strrchr(pic.jpg,'.'), it will return .jpg, do you understand? This function returns the character after the last position of the specified character in the string String. With substr(), we can get 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 used as needed in actual use Add.

Next, we call the function to determine the file type and convert it to lowercase strtolower($_FILES['file']['name']), here There is a very critical thing $_FILES, which is a super global array that saves the form data that needs to be processed. If register_globals is turned on, you can also access it directly, but this is unsafe. Look at the one just now Upload interface<input name="file" type="file">, 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 the file size
$_FILES['file']['type']--get File MIME type

With this information, you can easily determine the file information. Isn’t it very convenient? ^_^, there are some functions that need to be understood next,

file_exists()--determine whether the specified directory exists. If it does not exist, of course we cannot upload it
is_uploaded_file--Determine whether the file has been uploaded through HTTP POST
move_uploaded_file--Move the uploaded file to the specified directory

Success Upload, we will output a preview, otherwise the output upload will fail

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