What is the significance of the error message "Warning: Cannot modify header information - headers" in PHP?

The error message "Warning: Cannot modify header information - headers" in PHP occurs when there is an attempt to modify the HTTP headers after they have already been sent to the browser. This can happen if there is any output (such as HTML, whitespace, or error messages) before calling functions like header() or setcookie(). To solve this issue, make sure to call header() or setcookie() functions before any output is sent to the browser. 

<?php
ob_start(); // Start output buffering

// Your PHP code here

// Example of setting a header
header('Location: https://www.example.com');

ob_end_flush(); // Flush output buffer
?>

Keywords

header information modify warning PHP significance

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