Header warnings

[mjsulliv]

In my ongoing but scattered learning / work on web programming I’ve more than once encountered a “header” problem. In the most recent occurrence I found something interesting as described below. I have a php file called from another page via “onclick="location.href=…”. The called page uses a “session_start()” call to get access to global variables. When the enclosing “<?php “ is NOT on the very first line of the file I get:

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent…

But if it is on the first line there is no error. I’d love to know why this is. Any thoughts would be appreciated.

[thescientist]

it means something is sending something to the web browser before your PHP starts. this can include whitespace. so make sure the opening <?php is the very first line.

[HungryMind]

Hi!I Think You Are Using session_start(); In Your Page Multiple Times, Check Out First...If Not... Then Add These Codes:<?php ob_start(); ?> session_start(); // Be Sure That You Are Using session_start(); 1 Time In 1 One.?>Your All CODE<?php ob_flush();?>OR<?php ob_start(); ?> session_start(); // Be Sure That You Are Using session_start(); 1 Time In 1 One. //Your All CODE ob_flush();?>

[justsomeguy]

There's a description about what causes that error and how to solve it here:http://w3schools.invisionzone.com/index.php?showtopic=12509

[mjsulliv]

http://w3schools.invisionzone.com/index.php?showtopic=12509

Yes! A great explanation of what's going on in my code; though "headers" themselves are still fuzzy.Thanks --- MikeBTW I like your reference / link to Babbage. From my history of science classes in college I remember his concern about human "transcription" being one of the biggest problems in information handling; thus his construction of a printing device for mechanical calculators.

[justsomeguy]

Indeed. He correctly assumed that humans would be the greatest source of errors in computers.