Questions about the session Save verification Code

Session Save Verification Code problem
I have saved the original character of the code page from the other page in the session. How can it be empty? Strange

SOURCE program for code

checknum.php
Session_Start ();
function Random ($len)
{
$srcstr = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
Mt_srand ();//configuration of random seeds
$strs = "";
for ($i =0; $i < $len; $i + +) {
$strs. = $srcstr [Mt_rand (0,35)];
}
/*
2 Name: Strtoupper
3 function: string full capitalization \ r
4 return Value: string
5 Syntax: Strtoupper (string str);
6 Description: This function will turn the string str all the size of the string. \ r
7 Example:
8 Strtoupper ("AB2CD4EFG"); The result is AB2CD4EFG
9 Strtoupper ("AB1CDE4FG"); The result is AB1CDE4FG
10
11 */
Return Strtoupper ($STRS);
}
$str =random (4); Randomly generated string
$width = 50; Verify the width of the code picture
$height = 25; Verify the height of the code picture
/*
Content-type:xxxx/yyyy
Location:xxxx:yyyy/zzzz
status:nnn xxxxxx
*/
@header ("Content-type:image/png");
$_session["Code" = $str;
Echo $str;
$im =imagecreate ($width, $height);
Background color
$back =imagecolorallocate ($im, 0xff,0xff,0xff);
Blur Point Color
$pix =imagecolorallocate ($im, 187,230,247);
Font Color
$font =imagecolorallocate ($im, 41,163,238);
The point of painting blur function
Mt_srand ();
for ($i =0; $i <1000; $i + +)
{
Imagesetpixel ($im, Mt_rand (0, $width), Mt_rand (0, $height), $pix);
}
Imagestring ($im, 5, 7, 5, $STR, $font);
Imagerectangle ($im, 0,0, $width-1, $height-1, $font);
Imagepng ($im);
Imagedestroy ($im);
$_session["Code" = $str;

Session_destroy ();
?>


Calling $_session["code" from another page is actually empty? Why

------Solution--------------------
Session_destroy ();
You have deleted the session, how can another page have the content of the session?
------Solution--------------------
Session_destroy (); Halo, you have not yet taken off the session () How do you take it? 》

