How can HTML code before the header(location) function impact its effectiveness in preventing re-execution of POST actions in PHP?

Placing HTML code before the header(location) function in PHP can impact its effectiveness in preventing re-execution of POST actions because any output sent before the header function will cause it to fail. To ensure the header function works correctly, make sure there is no output (including HTML code) before it in the PHP script. 

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

// Your PHP code here

ob_end_clean(); // Clear output buffer without sending output

header("Location: new_page.php"); // Redirect to new page
exit; // Stop further execution
?>

Keywords

HTML code header function re-execution POST actions PHP

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