Cannot modify header information – headers already sent

The “Cannot modify header information – headers already sent” error is incredibly common, and I receive many many questions from all over about what it is and what caused it. So let’s clear all of this up once and for all.Upon doing a Google search for this error, I found many helpful articles, but none that were quite helpful enough – they give tips, but some of the details were a bit fuzzy.
But there are lots of useful solutions for this problem –

Echo before header

<?php
echo "hello world"
...
header('Location: http://...');
?>

 

Solution:

RemoveRemove the echo before header

Use ob_start(); and ob_end_flush(); for buffered output

New-line characters or spaces before <?php

 <?php
... header('Location: http://...');
?>

 

Solution:

Remove everything before <?php

Header Location in mixed php/HTML

<html>
...
<body>
...
<?php header('Location: http://...'); >
...
</body>
</html>

 

Sorry, you cannot use header-location here, because the header and the HTML code have already been sent!

 

Empty lines, chars or spaces after ?> when using an php include file

<?php
...
?>

 ... 
...

 

Solution:

Remove everything after ?> in the php include file

or

This normally can be resolved by a quick custom php.ini alteration:
1) Create a custom php.ini file (if there isn’t one already)

For information on how to create a custom php.ini file, please use other source.

2) Locate the line that looks like:

output_buffering = Off

3) Change the output_buffering line to:

output_buffering = On

This should be all that is needed to bring the site back online.

Lokesh

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