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Warning: Cannot modify header information – headers already sent!

warning: headers already sent

Posted in: Learned along the way
By: Blockcoder ( Admin ) / August 5th, 2011
Stats: 3 responses / Views: 174

Little sympathy

Okay first, i’m not going to explain what causes that warning message, but i’m explaining how to get rid of it. ( Because you don’t want to read so long story. )

Yes, i struggled with that problem for many hours and if I was frustrated with it, you are probably too.

Now, let us focus into the problem:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">



    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>Your title</title>



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



Above, we are sending header information within our php or html code. In this simple example I want browser to take me to the index of blockcoders.net. And after this we are getting this frustrating warning message about header already sent!

Getting rid of it:

We can get rid of it by using ob_start(); and ob_flush(); -php functions. With these we are declaring WHEN we are sending the output buffers.

The warning message says: “headers already sent…” so if we flush output buffer AFTER we use header(); function ( and all of our other possible output data ), it will work:

//make sure HERE is no empty rows or any white space!
<?php ob_start(); ?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

  header( 'Location: http://www.blockcoders.net' );

<?php ob_flush(); ?>

Make sure there are no white spaces at the beginning or at the end of your html or php code!

This was a really simplified example how to kick off the problem. BUT, I’m 100% sure that you won’t get that annoying warning message again!

Thanks folks, hope it helps :)

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