cannot use cookies in cURL PHP

I'm using cURL to parse a website.

http://www.hcmiu.edu.vn/bookforsale/showbooks.php

It need session to view, if you don't have session then the page redirect to :

http://www.hcmiu.edu.vn/bookforsale/perInfo.php

I use this code to get session coo开发者_Go百科kie but I don't know why I cannot see any change to file cookies.txt

$urltopost = "http://www.hcmiu.edu.vn/bookforsale/perInfo.php";
$datatopost = array (
"name" => "abc",
"tel" => "99999999",
"email" => "abc@gmail.com",
"profession" => "abc",
"employer" => "abc",
"tel_work" => "99999999",
); 
$ch = curl_init($urltopost);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $datatopost);

curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HEADER, true);
curl_setopt($ch, CURLOPT_COOKIEJAR, "/tmp/cookies.txt"); 

$returnData = curl_exec($ch);
$file = fopen("example.txt", "w");
fwrite($file, $returnData);
fclose($file);
curl_close($ch);

However, I see:

Set-Cookie: PHPSESSID=1egb993objkrdp3gi5mpvs02g0; path=/ 

in the header. Thanks for any help

-Edit: I use a tricky way: I use http viewer to view the PHPSESSID in browser cookies. And then I use it to to create a cookies file for cURL to read. Then I could pass the session checking of the web server for viewing file showbooks.php .

I used this code snippet to extract the cookie from the server's response:

$returnData = curl_exec($ch);
$cookie = '';
$pattern = '/Set-Cookie:(.*?)\n/';
if (preg_match($pattern, $returnData, $result))
$cookie = $result[1];

I've described my experience in this post. This approach doesn't use cookie file.

What concerns cookie file, consider the following advice from http://php.net/manual/en/book.curl.php:

Use absolute path for setting the variables CURLOPT_COOKIEFILE & CURLOPT_COOKIEJAR. To make life easier use the realpath("file.txt") function to get the absolute path.

is the file writable? does it even exist?

Try creating the file and give it global read write privilege.

Also try with a relative path (say, ./cookies.txt) instead of an absolute path for the cookie jar file.