What is the significance of the error message "Warning: Cannot modify header information - headers already sent by" in PHP?

The error message "Warning: Cannot modify header information - headers already sent by" in PHP indicates that there was output (such as whitespace or HTML) sent to the browser before the PHP header() function was called. To solve this issue, make sure that there is no output sent to the browser before calling header() function, and also check for any whitespace before the opening <?php tag in your PHP files. 

&lt;?php
ob_start(); // Output buffering starts
// Your PHP code here
ob_end_clean(); // Output buffering ends and clears the buffer
header(&quot;Location: example.php&quot;);
exit;
?&gt;

Keywords

PHP header information headers already sent warning modify

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