How to Fix “Headers Already Sent” Error in PHP

The “Headers already sent” error in PHP occurs when output is sent to the browser before the header() function is called.

This can disrupt session management and redirect operations. Here’s a quick fix:

Step 1: Check for Output Before Headers

Ensure no output (such as echo statements or HTML) is sent before calling header():

PHP
<?php
// Correct: Header function called before any output
header("Location: /newpage.php");
exit;
?>
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Step 2: Remove Whitespace

Check for any accidental whitespace or new lines outside the <?php ?> tags:

PHP
<?php
// Ensure no whitespace before or after PHP tags
?>
<!DOCTYPE html>
<html>
<head>
    <title>Example</title>
</head>
<body>
    <!-- Content -->
</body>
</html>
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Step 3: Use Output Buffering

If you need to send headers after some output, enable output buffering at the start of your script:

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PHP
<?php
ob_start(); // Start output buffering
header("Location: /newpage.php");
ob_end_flush(); // Send output buffer and turn off buffering
?>
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Conclusion

By following these steps, you can effectively resolve the “Headers already sent” error and ensure your PHP application handles redirects and sessions correctly.

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