session warning

Warning: Cannot send session cookie - headers already sent by (output started at e:wwwphpscripttestsession.php:3) in e:wwwphpscripttestsession.php on line 4

Why have got this warning when my script used session_start() function?
How to correct it?

When you use session_start() it sends a php session id to the client in the form a cookie.. cookies get sent as an HTTP header, so you need to session_start() before anything is sent to the client.

This means that you can't have any content before your <? tag and can't print anything before session_start().

If you are in control of the server, the way i'd do it is set the "output_buffering" setting to "on" and/or set the "session.auto_start" to "1" in the php.ini file.

If you're still having problems, show us some code?

//file testsession.php
...
3:<?
4:session_start();
5:$_SESSION['name'] = "EvilivE";
6:echo "This is page one. <br>The value of name is: ".$_SESSION['name']."<br>Goto page <a href="testsession1.php">two</a>";
?>
...

//file testsession1.php
...
3:<?
4:session_start();
5:echo "This is page two.<br>The value of name is: ".$_SESSION['name'];
6:session_destroy();
?>
...

when link to file testsession1.php the warning appear :
Cannot send session cookie - headers already sent by (output started at e:wwwphpscripttestsession.php:3) in e:wwwphpscripttestsession.php on line 4

note : the numbers are the line number of scripts.

I notice you're calling session_destroy _after_ the echo. try commenting out the echo, or putting the session_destroy before it (session_destroy does not, according to the manual, unset the variables associated to the session).. See if the problem is still happenning