PHP session variable not accessible on another page - php

Question

After trawling through other posts, I could not find the answer.
The problem is that when i create a custom session name, I am not able to access session variables on any other pages. How can I get this working with custom session variable?
Scenario A
Login page
after successful login, the following is called
function initiatenewsession($app, $userid){
$session_name = getuniquesessionid($app,$userid); // Set a custom session name
session_name($session_name);
session_start();
session_regenerate_id(true);
$_SESSION["loggeduserid"] = $user_id;
echo("1a)SESSION NAME[".session_name()."]");
echo("1b)logged user[".$_SESSION["loggeduserid"]."]");
}
Echo result
1a) SESSION NAME[myappsessionid6520150528184534]
1b) logged user[65]
Registration page (User clicks a link after logging in)
session_start();
echo("2a)SESSION NAME[".session_name()."]");
echo("2b)logged user[".$_SESSION["loggeduserid"]."]");
2a)SESSION NAME[PHPSESSID]
2b)logged user[]
Scenario B
Login page
after successful login, the following is called
function initiatenewsession($app, $userid){
session_start();
session_regenerate_id(true);
$_SESSION["loggeduserid"] = $user_id;
echo("1a)SESSION NAME[".session_name()."]");
echo("1b)logged user[".$_SESSION["loggeduserid"]."]");
}
Echo result
1a) SESSION NAME[PHPSESSID]
1b) logged user[65]
Registration page (User clicks a link after logging in)
session_start();
echo("2a)SESSION NAME[".session_name()."]");
echo("2b)logged user[".$_SESSION["loggeduserid"]."]");
2a)SESSION NAME[PHPSESSID]
2b)logged user[65]

Answer 1

As per my comment, when you do session_start(), php will check if you set a session name via session_name(), otherwise it'll use its default.
Session startup is basically like this, in php-ish pseudocode:
if (custom_session_name_was_set()) {
$session_name = get_custom_session_name();
} else {
$session_name = ini_get('session.name');
}
if (isset($_COOKIE[$session_name])) {
$id = $_COOKIE[$session_name];
} else {
$id = generate_new_random_id();
setcookie($session_name, $id);
}
$session_data = file_get_contents('/path/to/session/files/' . $id);
$_SESSION = unserialize($session_data);
For your first bit of code, you set a custom name, so that's the name that's used for the session cookie.
In your other code, you do NOT set a custom name, so php uses its default: PHPSESSID. Now you've got two sessions floating around, each with their own unique names, and their own different IDs, and their own separate data in $_SESSION.
If you're going to be using custom session names, you have do session_name($customName) EVERYWHERE you have session_start().

Answer 2

If using a custom session name you must call session_name().
You must call session_start() before headers_sent().
On servers with multiple PHP version support check phpversion() to ensure that the server did not decide to run the wrong version (and hence the wrong session_save_path()).