How do I declare a global variable in PHP I can use across templates?

Question

In wordpress, it calls header.php then whatever template name or the page requested. How can I declare a variable in my php header which I can then refer to in my other tem

Answer 1

I think php session is one of the way to use as a global variable on Wordpress.

1. Functions.php

if(!session_id()) {
    session_start();
}

2. Any .php file where you want set or get global variables

• get variable

  if(isset($_SESSION['global_var'])) {
      $local_var = $_SESSION['global_var'];
  }
  

• set variable

  $_SESSION['global_var'] = "This is global var";