How to prevent image cache file format in php

PHP is a widely used server-side scripting language that allows you to write PHP code for web applications and run it on the server. In PHP, you sometimes encounter some problems related to image caching. For example, when you open a website in a browser, its images cannot be updated or change very slowly. This is usually caused by the browser or server caching images. Therefore, this article will introduce you to how to make images cache-free file formats in PHP.

1. Forcing the browser not to cache images

By default, the browser will cache downloaded images, which can speed up access, but it also brings some problems . In PHP, you can use the header() function to control the browser's cache time by setting Cache-Control. For example:

<?php
header("Cache-Control: no-cache, no-store, must-revalidate"); //强制浏览器不缓存
header("Expires: 0"); //指定过期时间为0
?>

In this way, when the server returns a picture, it will set the HTTP response header to tell the browser not to cache this picture and download the latest picture from the server every time.

2. Add a random string to the URL of the image

This method is to make the browser think that it is a random string by adding a random string to the URL of the image. new pictures to download the latest pictures. The random string can be a timestamp, a UUID or a random number. For example:

<?php
$img_url = &#39;http://example.com/images/logo.png?rand=&#39; . uniqid(); //在图片URL中添加一个唯一标识符
echo &#39;<img src="&#39; . $img_url . &#39;">';
?>

In this example, by adding a random number after the URL, a new image will be downloaded every time the image is loaded.

3. Set the image to be non-cacheable on the server

The last method is to set the image to be non-cacheable on the server. In the Apache server, you can cancel the cache of images by adding the following code to the .htaccess file:

<FilesMatch "\.(jpg|png|gif)$">
  Header set Cache-Control "max-age=0, no-store"
</FilesMatch>

This code means that it only takes effect for .jpg, .png and .gif files and sets the response header. Cache-Control is "max-age=0, no-store". This will force the browser to download the latest images from the server every time.

Summary

By modifying the HTTP response header, adding random parameters to the URL, or setting the response header on the server, you can make images in PHP have no cached file format. In this way, the latest pictures can be displayed no matter which browser is used, bringing a better experience to users.

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