Using PHP header() Function: Syntax, Parameters, and Common Use Cases

In PHP, the header() function is a crucial tool that can perform page redirection and set HTTP response header information. This article provides a detailed introduction to the usage of header() and includes concrete code examples.

Basic Syntax of header()

<code>header(string $header, bool $replace = true, int $http_response_code = 0): bool</code>

$header (required): the HTTP header to send, e.g., "Content-Type: text/html;charset=utf-8".

$replace (optional): whether to replace a previous header of the same name; default is true .

$http_response_code (optional): the HTTP status code to set; must be a valid status code.

Common Scenarios and Code Examples

Implement Page Redirection

The header() function can redirect the user to a specified URL.

<code>header("Location: http://www.example.com");
exit;</code>

Set HTTP Response Headers

It can also set response headers such as Content-Type or Content-Disposition . For example, to set JSON content type:

<code>header("Content-Type: application/json");</code>

Set HTTP Response Status Code

The function can define the HTTP status code, e.g., 200 for success or 404 for not found.

<code>header("HTTP/1.1 404 Not Found");</code>

Prevent Page Caching

To stop browsers from caching a page, set cache‑control headers:

<code>header("Cache-Control: no-cache, no-store, must-revalidate");
header("Pragma: no-cache");
header("Expires: 0");</code>

Set File Download

By setting Content-Disposition to attachment , a file can be offered for download.

<code>header("Content-Disposition: attachment; filename=example.pdf");
header("Content-Type: application/pdf");
header("Content-Length: " . filesize("example.pdf"));
readfile("example.pdf");</code>

The header() function is versatile for both redirection and customizing HTTP headers, and developers should understand its parameters to use it effectively in various backend scenarios.