PHP 7 header() Function
Example
Send three HTTP headers to prevent page caching:
<?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: There are options that users may set to change the browser's default caching settings. By sending the headers above, you will override any of those settings and force the browser to not cache!
Definition and Usage
The header() function sends a raw HTTP header to a client.
It is important to notice that the header() function must be called before any actual output is sent!
Syntax
header(header, replace, http_response_code)
| Parameter | Description |
|---|---|
| header | Required. Specifies the header string to send |
| replace | Optional. Indicates whether the header should replace a previous similar header or add a new header of the same type. Default is TRUE (will replace). FALSE allows multiple headers of the same type |
| http_response_code | Optional. Forces the HTTP response code to the specified value |
Technical Details
| Return Value: | Nothing |
|---|---|
| PHP Version: | 4.0+ |
| PHP Changelog: | PHP 5.1.2: Now prevents that more than one header to be sent at once. This is a protection against header injection attacks |
More Examples
Example
Let the user be prompted to save a generated PDF file (Content-Disposition header is used to supply a recommended filename and force the browser to display the save dialog box):
<?php
header("Content-type:application/pdf");
// It will be called downloaded.pdf
header("Content-Disposition:attachment;filename='downloaded.pdf'");
// The PDF source is in original.pdf
readfile("original.pdf");
?>
<html>
<body>
...
...
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