PHP Variable Scope

Variable scope

In PHP, variables can be declared anywhere in the script.
The scope of a variable is the part of the script where the variable can be referenced/used.
PHP has three different variable scopes:

  • local
  • global
  • static
Local Scope:
A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function.
Global Scope:
A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function.

Example type Syntax:

<?php
    $a = 5; // Global scope
    // variable declared outside function

    function myFunction() {
        $b = 7; //Local scope
        // variable declared inside function
    }
?>

Example:

In the example, there are two variables $a and $b and a function myTest().
$a is a global variable since it is declared outside the function and $b is a local variable since it is created inside the function.

<?php
    $a = 5; // global scope

    function myTest() {
        $b = 7; // local scope
        echo "<p>Test variables inside the function:</p>";
        echo "Variable a is: $a";
        echo "<br />";
        echo "Variable b is: $b";
    } 

    myTest();

    echo "<p>Test variables outside the function:</p>";
    echo "Variable a is: $a";
    echo "<br />";
    echo "Variable b is: $b";
?>

When we output the values of the two variables inside the myTest() function, it prints the value of $b as it is the locally declared, but cannot print the value of $a since it is created outside the function.

Then, when we output the values of the two variables outside the myTest() function, it prints the value of $a, but cannot print the value of $b since it is a local variable and it is created inside the myTest() function.

Output:

Tutorialik.com

Test variables inside the function:

Variable a is: 
Variable b is: 7

Test variables outside the function:

Variable a is: 5
Variable b is:

PHP The global Keyword

The global keyword is used to access a global variable from within a function.
To do this, use the global keyword before the variables (inside the function):

Example:

<?php
    $a = 5; // global scope

    function myTest() {
        global $a;  //access global variable with global keyword
        
        $b = 7; // local scope
        echo "<p>Test variables inside the function:</p>";
        echo "Variable a is: $a";
        echo "<br />";
        echo "Variable b is: $b";
    } 

    myTest();
?>

Output:

Tutorialik.com

Test variables inside the function:

Variable a is: 5
Variable b is: 7

PHP The static Keyword

Normally, when a function is completed/executed, all of its variables are deleted.
However, sometimes we want a local variable NOT to be deleted. We need it for a further job.
To do this, use the static keyword when you first declare the variable:

Example:

<?php
    function myStaticTest() {
        static $a = 0;  // use of static keyword
        echo $a ;
        $a++;
    }

    myStaticTest();
    myStaticTest();
    myStaticTest();
?>

Then, each time the function is called, that variable will still have the information it contained from the last time the function was called.

Output:

Tutorialik.com
0 1 2

Just remove static keyword from example, and run it again. if you want to see difference!



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