help! cookie tracking...

[tom_chow]

I want to make a affiliate program just like cj.com.
I use cookies to track leads and sales from affiliates but failed.

here is what I have done:
We have site A:www.a.com and site B:ww.b.com

a1.php of site A:
<?
$timestamp=time();
$cookietime = $timestamp+36000;
$user="new";
setcookie('ckuser',$user,$cookietime);
?>

a2.php of site B:
<?
$userid=$HTTP_COOKIE_VARS['ckuser'];

$testrecordfile='test_record.txt';
$test_record="userid=$userid\n";

writefile($testrecordfile,$test_record,"ab");
//echo $test_record;

function writefile($filename,$data,$method="rb+",$iflock=1){
touch($filename);
$handle=fopen($filename,$method);
if($iflock){
flock($handle,LOCK_EX);
}
fputs($handle,$data);
if($method=="rb+") ftruncate($handle,strlen($data));
fclose($handle);
}
?>

test.html of site B:
<img src=http://www.a.com/a2.php>

When I open test.html on site B, I got userid=NULL in
'test_record.txt' .

Why can't I use cookie to track user? Anyone have good idea of tracking sales or leads of affiliates on merchant's site?

Thanks.

[Weedpacket]

Most users who know how would prevent this from working as a security precaution, anyway; but if you look at the manual page for [man]setcookie[/man], you'll find links to the cookie specification, which would indicate what is needed (as would the setcookie page itself, where it mentions "domain").