What does the error "Cannot modify header information - headers already sent" mean in PHP?

The error "Cannot modify header information - headers already sent" in PHP occurs when your script tries to send HTTP headers after content has already been sent to the browser. To solve this issue, ensure that no output is sent to the browser before calling functions like header() or setcookie(). You can use ob_start() to buffer output and prevent headers from being sent prematurely. 

<?php
ob_start();
// Your PHP code here

// Example of setting a header after output has already been sent
echo "Hello, World!";
header("Location: https://www.example.com");
ob_end_flush();
?>

Keywords

PHP header information headers already sent error message output buffering

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