PHP global keyword and variable scope

On PHP the great quantity of variables have a single scope.

<?php
   $variable = "hola mundo";
   include "archivo.php";
?>

The variable $varaible is disponible in archive.php except in function. Inside functions variables are in local scope, you can access varaibles inside that function.

When we are using functions, we have 3 different situations in where we can access the parent scope: using referenced parameter; second, using global inside the function to access the variable that is $GLOBALS array; 3 using use in anonymous function.

<?php
function myfunction(){
	$local = "this is a local variable";
	echo "inside function:".$local;
}
myfunction();
echo $local;

inside function:this is a local variable
Notice: Undefined variable: local in /home/user/scripts/code.php on line 8

$parent ="text not defined";
function myfunction($local){
	$local = "this is a local variable";
	echo "inside function:".$local."\n";
}
myfunction($parent);
echo $parent;

inside function:this is a local variable
text not defined

When we change the variable inside the function this one not change the parent variable $local

Parameter passed by reference.

As we see before, when a variable is passed by reference, this will change the parent value if this one is modified.

<?php

$parent ="text not defined";
function myfunction(&$local){
	$local = "this is a local variable";
	echo "inside function:".$local."\n";
}
myfunction($parent);
echo $parent;

inside function:this is a local variable
this is a local variable

Now $parent will have the value “this is a local variable”

Using use in Anonymous Functions

Since PHP 7 we can use the term use in anonymus functions that permit us to use a variable from the parent scope.

<?php

$message ="mort dijo: Hola tu";
$example = function () use ($message): string {
    return $message;
};

echo $example();

Watch that we are using $example() and not $example this is cause that $example is an object(closure).

The keyword global y $GLOBAL

Inside a function, we can use global world that permit access to the global variable, for example global $a permit us use $GLOBALS[‘a’].

If you execute the following code and take a look at the variable value $a would not be more “hello word”, it would be “Bienvenidos”.

<?php
function cambioDeTexto(){
   global $a;
   $a = "Bienvenido";
}

$a = "hello word";
echo "<p>$a</p>";
cambioDeTexto();
echo "<p>$a</p>";

hello word

Bienvenido

In this case $a is a global variable and is in $GLOBALS array. Probably this example makes you wonder

¿single scope are global variables? Lets check that.

<?php
$a = "hola";
echo $GLOBALS["a"];

hola