Header means header, which is a built-in http function in php, used to send the original HTTP header to the client. Its usage syntax is "header(string,replace,http_response_code)"; the parameter string Specifies the header string to be sent. Headers are commonly used to notify the browser that the page does not exist, delay redirection, indicate content type, declare downloaded files, disable caching of the current document, display a login dialog box that requires verification, etc.
The operating environment of this article: windows7 system, PHP8 version, DELL G3 computer
header means header.
php header() function sends the original HTTP header to the client. It is often used to notify the browser that the page does not exist, delay redirection, indicate content type, declare downloaded files, and Disable caching of the current document, display a login dialog requiring authentication, etc.
The header function is commonly declared in settings:
header('HTTP/1.1 200 OK'); // ok 正常访问 header('HTTP/1.1 404 Not Found'); //通知浏览器 页面不存在 header('HTTP/1.1 301 Moved Permanently'); //设置地址被永久的重定向 301 header('Location: http://www.ithhc.cn/'); //跳转到一个新的地址 header('Refresh: 10; url=http://www.ithhc.cn/'); //延迟转向 也就是隔几秒跳转 header('X-Powered-By: PHP/6.0.0'); //修改 X-Powered-By信息 header('Content-language: en'); //文档语言 header('Content-Length: 1234'); //设置内容长度 header('Last-Modified: '.gmdate('D, d M Y H:i:s', $time).' GMT'); //告诉浏览器最后一次修改时间 header('HTTP/1.1 304 Not Modified'); //告诉浏览器文档内容没有发生改变
It is important to realize that the header() function must be called before any actual output is sent (in PHP 4 and higher version, you can use output caching to solve this problem):
<html> <?php // 结果出错 // 在调用 header() 之前已存在输出 header('Location: http://www.example.com/'); ?>
Syntax
header(string,replace,http_response_code)
Parameters
string Required. Specifies the header string to be sent.
-
replace
Optional. Indicates whether this header replaces the previous header, or adds a second header.
The default is true (replacement). false (allow multiple headers of the same type).
http_response_code Optional. Forces the HTTP response code to the specified value. (Available in PHP 4 and above)
Note: From PHP 4.4 onwards, this function prevents multiple headers from being sent at once. This is a protection measure against header injection attacks.
Example
Example 1
<?php
// Date in the past
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
header("Cache-Control: no-cache");
header("Pragma: no-cache");
?>
<html>
<body>
...
...Note: The user may set some options to change the browser's default cache settings. By sending the header above, you can override any of these settings and force the browser not to cache!
Example 2
Prompts the user to save a generated PDF file (the Content-Disposition header is used to provide a recommended file name and force the browser to display a save dialog):
<?php
header("Content-type:application/pdf");
// 文件将被称为 downloaded.pdf
header("Content-Disposition:attachment;filename='downloaded.pdf'");
// PDF 源在 original.pdf 中
readfile("original.pdf");
?>
<html>
<body>
...
... Note: Microsoft IE 5.5 has a bug that prevents the above mechanism. This bug can be resolved by upgrading to Service Pack 2 or later.
[Recommended learning: "PHP Video Tutorial"]
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