Scope

Determines when and where a variable can be used.

Can also be thought of as the lifetime or validity of the variable.

4 scope types:

Global
Local
Function Parameters
Static

Global Scope

Any variable defined outside of any function
Can be accessed from any part of the script that is not inside a function
Use the global keyword to access a global variable from within a function

<?php
	$myGlobal = 6;		//global variable
	$yourGlobal = 7 ;	//global variable

	echo $myGlobal * $yourGlobal . "<br>";

	function multiplyNoGlobal()
	{
		//unable to use global variables without using global keyword
		echo $myGlobal * $yourGlobal . "<br>";
	}

	multiplyNoGlobal();

	function multiplyGlobal()
	{
		global $myGlobal, $yourGlobal ;	//use global variables
		echo $myGlobal * $yourGlobal . "<br>";
	}

	multiplyGlobal();

?>

<?php

$myGlobal = 6; //global variable

$yourGlobal = 7 ; //global variable

echo $myGlobal * $yourGlobal . " ";

function multiplyNoGlobal()

{

//unable to use global variables without using global keyword

echo $myGlobal * $yourGlobal . " ";

}

multiplyNoGlobal();

function multiplyGlobal()

{

global $myGlobal, $yourGlobal ; //use global variables

echo $myGlobal * $yourGlobal . " ";

}

multiplyGlobal();

Displays:

The $GLOBALS[ ] array also stores global variables, using the name of the variable as the index:

<?php
	$myGlobal = 6;		//global variable
	$yourGlobal = 7 ;	//global variable

	function globalsArray()
	{
		//use $GLOBALS array with global variables as index
		echo $GLOBALS['myGlobal'] * $GLOBALS['yourGlobal'] . "<br>";
	}

	globalsArray();

?>

<?php

$myGlobal = 6; //global variable

$yourGlobal = 7 ; //global variable

function globalsArray()

{

//use $GLOBALS array with global variables as index

echo $GLOBALS['myGlobal'] * $GLOBALS['yourGlobal'] . " ";

}

globalsArray();

Displays:

Local Scope

A locally scoped variable is only valid within the block of code in which it has been declared.

<?php
	$myVar = 6;		//global variable

	function localScope()
	{
		//Will display nothing as has no local value
		echo $myVar . "nothing here<br>";

		//assign a value to give local scope
		$myVar = 42;
		echo $myVar . "<br>";
	}

	localScope();

	//display current scoped variable
	echo $myVar;

?>

<?php

$myVar = 6; //global variable

function localScope()

{

//Will display nothing as has no local value

echo $myVar . "nothing here ";

//assign a value to give local scope

$myVar = 42;

echo $myVar . " ";

}

localScope();

//display current scoped variable

echo $myVar;

Displays:

nothing here

Function Parameters

Objects passed to a function as arguments to be used within the function

Only valid within the function

<?php

	function parameters($myVar, $yourVar)
	{
		echo "The two variables passed in were: " . $myVar . " and ". $yourVar . "
";

	}

	$firstVar = "Excellent";
	$secondVar = 12 ;
	parameters($firstVar, $secondVar);

?>

<?php

function parameters($myVar, $yourVar)

{

echo "The two variables passed in were: " . $myVar . " and ". $yourVar . "

}

$firstVar = "Excellent";

$secondVar = 12 ;

parameters($firstVar, $secondVar);

Displays:

The two variables passed in were: Excellent and 12

Static Variables

Use static keyword within a function to make the variable retains its previous value

The variable still remains local to that function and cannot be used outside of the function

<?php

	function remembering() {

	STATIC $myVar = 0;
	   $myVar++;
	   echo "\$myVar is now: " . $myVar . "
" ;
	}
	remembering();
	remembering();
	remembering();
	remembering();
	remembering();

?>

<?php

function remembering() {

STATIC $myVar = 0;

$myVar++;

echo "\$myVar is now: " . $myVar . "

" ;

}

remembering();

Displays:

$myVar is now: 1
$myVar is now: 2
$myVar is now: 3
$myVar is now: 4
$myVar is now: 5

This example shows a bad function (salmon shaded area) without using the global keyword to use the global variable.
Which is then followed by a good function (lilac shaded area) using the global keyword to use the global variable.
Finally it shows that the local variable within a function is non-existent outside of the function:

Displays:

$myVar in global scope is: 5.

Function NOT using global variable:
$myVar inside function is: .
Locally scoped $newVar inside function is: 0.

Function USING global variable:
$myVar inside function is: 5.
Locally scoped $newVar inside function is: 25.

Global $myVar is: 5.
Previously locally scoped $newVar outside the function is: .

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