How to access a global variable from within a class constructor

Question

For example I have 3 files:

First index.php with following code :

<?php
  include("includes/vars.php");
  include("includes/test.class.php");

  $test = new test();
?>

then vars.php with following code:

<?php
  $data = "Some Data";
?>

and last test.class.php

 <?php
 class test 
{
  function __construct()
  {
    echo $data;
  }
}
?>

When I run index.php the Some Data value from $data variable is not displayed, how to make it to work?

Answer 1

Reading material.

Because of scope. Data is within the global scope and the only thing available within a class are variables and methods within the class scope.

You could do

class test 
{
  function __construct()
  {
    global $data;
    echo $data;
  }
}

But it is not good practice to use global variables within a class.

You could pass the variable into the class via the constructor.

class test 
{
  function __construct($data)
  {
    echo $data;
  }
}

$test = new test("test");