PHP global variables in function and class

Joined:
03/10/2011: Posts:
84

April 28, 2011 21:09:08 Last update: April 28, 2011 21:09:08

PHP global variables are defined outside of functions and classes. They are visible both in the current file and in any included/required files. Also, any global variables defined in required/included files are visible in the current file. But they are not visible in any functions or classes, unless specifically declared global.

Test:

Create file test.php:

<?php
ini_set('display_errors', 'stderr');
ini_set('error_reporting', E_NOTICE);

// $a and $b available in test.inc
$a = 'a';
$b = 'b';

include "test.inc";

echo '[', __FILE__, '] $c + $d = ', $c + $d, "\n";

function concat() {
    echo '[', __FUNCTION__, '] $a . $b = ', $a . $b, "\n";
}

function concat_global() {
    global $c, $d;
    echo '[', __FUNCTION__, '] $c + $d = ', $c + $d, "\n";
}

class A {
    function __construct() {
	echo '[', __CLASS__, '] $c + $d = ', $c + $d, "\n";
    }
}

class B {
    var $e = 'e';
    private $f = 'f';
    function __construct() {
	global $a, $b;
	echo '[', __CLASS__, '] $a . $b = ', $a . $b, "\n";
	echo '[', __CLASS__, '] $e . $f = ', $e . $f, "\n";
	echo '[', __CLASS__, '] $this->e . $this->f = ', $this->e . $this->f, "\n";
    }
}

concat();
concat_global();
new A();
new B();
?>

Create file test.inc:

<?php
    echo '[', __FILE__, '] $a . $b = ', $a . $b, "\n";

    // $c and $d available in test.php
    $c = '1';
    $d = '2';
?>

Run the PHP script in command line:
```
php test.php 2>C:\tmp\stderr.out
```

The result is:

[C:\work\test.inc] $a . $b = ab
[C:\work\test.php] $c + $d = 3
[concat] $a . $b =
[concat_global] $c + $d = 3
[A] $c + $d = 0
[B] $a . $b = ab
[B] $e . $f =
[B] $this->e . $this->f = ef

stderr messages:

PHP Notice:  Undefined variable: b in C:\work\scrap\test.php on line 14
Notice: Undefined variable: b in C:\work\scrap\test.php on line 14
PHP Notice:  Undefined variable: a in C:\work\scrap\test.php on line 14
Notice: Undefined variable: a in C:\work\scrap\test.php on line 14
PHP Notice:  Undefined variable: d in C:\work\scrap\test.php on line 24
Notice: Undefined variable: d in C:\work\scrap\test.php on line 24
PHP Notice:  Undefined variable: c in C:\work\scrap\test.php on line 24
Notice: Undefined variable: c in C:\work\scrap\test.php on line 24
PHP Notice:  Undefined variable: f in C:\work\scrap\test.php on line 34
Notice: Undefined variable: f in C:\work\scrap\test.php on line 34
PHP Notice:  Undefined variable: e in C:\work\scrap\test.php on line 34
Notice: Undefined variable: e in C:\work\scrap\test.php on line 34

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PHP global variables in function and class