how to use ob_start();

how to use ob_start? what is its function?

In last few forum, i have post my problem and i get the response tat suggest i can use the ob_start.

But i not really understand its meaning n how to use in my coding ??

i add ob_start(); at the top of coding but my problem still can't settle.

Warning: Cannot send session cache limiter - headers already sent (output started at c:\web\wai\cart.php:3) in c:\web\db.php on line 43


*php code

function GetCartId()
{
if(isset($_COOKIE["cartId"]))
{
return $_COOKIE["cartId"];
}
else
{

session_start();
setcookie("cartId", session_id(), time() + ((3600 * 24) * 30)); (line 43)
return session_id();
}
}

can i know what is the problem and how to use ob_start(); which suggest for me in last forum?10q

ob_start(); clears the browser's header.

what i do in my scripts i add ob_start(); at the top of the page & ob_end_flush(); at the bottom.. so:



the cause of your problem may not be because you did not use ob_start(); check to make sure you dont have any whitespace or newlines.

Actually, ob_start() tells PHP to start output buffering, meaning that anything you output after ob_start() wont be sent to the browser until the end of the page or ob_end() etc are reached.

So that means that once you use ob_start() and echo something out, you can still set cookies without any errors. For example:

<?php

ob_start();
echo "this will work";
setcookie("test", true);

ob_end_flush();

?>

etc...

is it whitespace or newlines mean like print,echo???

i should check that in that page? in whole db.php i didn't put any echo on it.

tat is whole coding in db.php(same as in tutorial)

<?


$dbServer = "localhost";
$dbUser = "user";
$dbPass = "password";
$dbName = "db";

function ConnectToDb($server, $user, $pass, $database)
{
// Connect to the database and return
// true/false depending on whether or
// not a connection could be made.

$s = @mysql_connect($server, $user, $pass);
$d = @mysql_select_db($database, $s);

if(!$s || !$d)
return false;
else
return true;
}


function GetCartId()
{
// This function will generate an encrypted string and
// will set it as a cookie using set_cookie. This will
// also be used as the cookieId field in the cart table

if(isset($_COOKIE["cartId"]))
{
return $_COOKIE["cartId"];
}
else
{
// There is no cookie set. We will set the cookie
// and return the value of the users session ID

session_start();
setcookie("cartId", session_id(), time() + ((3600 * 24) * 30));
return session_id();
}
}


?>

actually my shopping cart can run and function but just in the top of shopping cart appear the warning like that

Warning: Cannot send session cache limiter - headers already sent (output started at c:\web\wai\cart.php:3) in c:\web\db.php on line 43

how i can make it disappear??

thanks to mytch for enlightening me

try adding ob_start(); just before you set your cookie and ob_end_flush(); after you set it.

as mytch said ob_start buffers the header, so its not sent out till the end of the page, or you use ob_end, etc

in your case wailin, using $_COOKIES, sets the header. If you do what war-angel said, by placing a ob_start before your cookie call it should stop the header being sent out, which will stop that message from apearing.

here are some functions/variables that set the header.

$_COOKIE
setcookie
header

if you want to find out at any stage if the headers have already been sent (this is good for debugging)
try using this function

headers_sent

returns true if headers have been sent.

Just to clarify, ob_start() buffers content NOT headers.

Hadley