Analysis on the scope of application of php global variables

$a = 1 ;
include 'b.inc' ;
?>

Here variable $a will take effect in the include file b.inc. However, in user-defined functions, a local function scope will be introduced. Any variables used inside a function will be restricted to the local function scope by default.

$a = 1 ; /* global scope */
function Test ()
{
echo $a ; /* reference to local scope variable */
}
Test ();
?>

This script will not produce any output, because the echo statement refers to a local version of the variable $a, and it is not assigned a value in this scope. You may notice that PHP’s global variables are a little different from those in C Global variables in PHP must be declared global (global keyword) when used in functions.

$a = 1 ;
$b = 2 ;
function Sum ()
{
global $a , $b ;
$b = $a + $b ;
}
 Sum ();
echo $b ;
?>

The above script will output: "3".