Access variable defined in other file from class - php

Question

I would like to know if there is a way to access a variable defined in an other file from a class in PHP.
Example :
file_01.php
<?php
$a = 42;
?>
file_02.php
<?php
require_once('file_01.php');
class mnyClass
{
private $myVar;
function __construct($var = $a)
{
$this->myVar = $var;
}
function getVar()
{
return $this->var;
}
function setVar($var)
{
$this->myVar = $var;
}
}
?>
Obviously, my class is more complicated. I have chosen this example for a better comprehension of what I try to do ;)
Thank you in advance.

Answer 1

You cannot do this:
function __construct($var = $a)
{
$this->myVar = $var;
}
What you can do is pass it:
<?php
require_once('file_01.php');
$mnyClass = new mnyClass($a);// the torch has been passed!
class mnyClass
{
private $myVar;
function __construct($var = null)
{
$this->myVar = $var;
}
function getVar()
{
return $this->var;
}
function setVar($var)
{
$this->myVar = $var;
}
}
?>
OR you can do this (it is not advisable):
function __construct($var = null)
{
if($var === null) $var = $GLOBALS['a']; //use global $a variable
$this->myVar = $var;
}

Answer 2

You could access the variable via GLOBALS:
http://php.net/manual/en/language.variables.scope.php
EDIT: a little more detail-
function __construct() {
$this->myVar = $GLOBALS['a'];
}

Answer 3

It sounds like you're setting up some application defaults. It might make sense to define these as constants:
file_01.php:
define('DEFAULT_VALUE_FOR_A', 42);
file_02.php
class myClass
{
function __construct($var = DEFAULT_VALUE_FOR_A) {
}
}

Answer 4

Finally, I use this method :
<?php
require_once('file_01.php');
class myClass {
private $myVar;
function __construct($var = NULL)
{
global $a;
if($var == NULL)
$this->myVar = $a;
else
$this->myVar = $var;
}
}
?>
I declare my variable $a as global in the constructor, set the default value of my $var to NULL and check if the constructor was called with parameter(s) ($var == NULL).