headers sent to early problem

PureDrive

I have a page which contains a form. I submit the information to the same page via post data. If a certain variable is set then I use the php header function to redirect to another page and I also pass a certain key variable using get data to the other page. Everything was working fine until I included 'Prototype' which is a javascript/ajax library. When I include this file (prototype.js), I get this warning:

"Warning: Cannot modify header information - headers already sent by (output started at C:\web programming\Omega III\scripts\js\prototype.js:114) in C:\web programming\Omega III\scripts\strength\add_workout.php on line 71"

I went to the file and looked at line 114 and this is what I get:

 if (object === undefined) return 'undefined';

What does this have to do with sending headers? I don't think anything happens at that point since no function in that file is being called. Any suggestions?

NogDog

All HTTP headers must be sent before the actual page content is sent. Therefore, once any of your code generates actual output (including anything - text or white-space - outside of <?php...?> tags), then PHP causes all pending headers to be sent at that time. From that point forward, no more headers can be sent. Therefore you cannot use any PHP function that creates additional headers, including header(), setcookie(), session_start(), etc.

Your two options are to either (1) re-arrange your code so all processing that might cause any HTTP headers to be generated occurs before any output is generated, or (2) use the output-buffering functions to postpone output until you want it to occur. Option 2 may (emphasis on "may") cause a small performance hit due to the additional processing/memory that may be required.