What are common reasons for the "headers already sent" error when using the header function in PHP?

The "headers already sent" error in PHP occurs when the header function is called after output has already been sent to the browser. This can happen due to whitespace or HTML content being sent before the header function is called. To solve this issue, ensure that the header function is called before any output is sent to the browser. 

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

// Your PHP code here

header("Location: https://www.example.com");

ob_end_flush(); // Flush output buffer
?>

Keywords

PHP headers header function output buffering whitespace

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