how to generate unique session ID without the use of session_id()? - php

Question

I want to generate a session ID. This unique sessionId represents some different data for every different user.
My code till now:
onclick and onload of a page I call a function create_session_id();
function create_session_id() {
// This function sends a string to a PHP page using ajax post.
}
On my PHP page, I receive this data and then insert it:
session_start();
$a = session_id();
$object->insert_sessionid($a);
My Question
Is it possible to use only session_start() (no session_id()) and store some unique session ID value that I can use later when I fetch data and throw data to my web page. I don’t want any clicks to register sessionid. It should happen on page load and without any function create_session_id().
I am thinking to bring some cookies in to the picture.
Note: My website doesn’t allow login.

Answer 1

use a function like
function createRandomVal($val){
$chars="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789,-";
srand((double)microtime()*1000000);
$i = 0;
$pass = '' ;
while ($i<=$val)
{
$num = rand() % 33;
$tmp = substr($chars, $num, 1);
$pass = $pass . $tmp;
$i++;
}
return $pass;
}
and pass return value in session id

Answer 2

The above code is a little bit buggy since user669677 has edited it.
Here is the proper code:
function createRandomVal($val) {
$chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789,-";
srand((double)microtime() * 1000000);
$i = 0;
$pass = '';
while ($i < $val) {
$num = rand() % 64;
$tmp = substr($chars, $num, 1);
$pass = $pass . $tmp;
$i++;
}
return $pass;
}