How can the issue of not being able to set headers after sending output (HTML) be resolved in PHP?

When PHP code sends any output (such as HTML content) to the browser, it becomes impossible to set HTTP headers afterwards. To resolve this issue, make sure to set any necessary headers before any output is sent to the browser. 

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

// Set headers before any output
header("Content-Type: text/html");

// Output HTML content
echo "<html><body><h1>Hello, World!</h1></body></html>";

ob_end_flush(); // Flush the output buffer
?>

Keywords

output buffering ob_start ob_end_flush headers_sent flush

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