Impara Variable Scope in Functions

Definition

Variable scope refers to the part of a program where a variable can be accessed or used. It determines whether a variable is available inside functions, outside functions, or across multiple function calls.

To write reliable functions in PHP, it's important to understand how variable scope works. A variable's scope defines where it can be accessed and how long it remains available during execution. When working with functions, PHP uses three main types of scope: local, global, and static.

A local variable is declared inside a function and can only be used within that function. After the function finishes running, the variable is destroyed and its value is no longer available.

variable_scope.php


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<?php
// Global variable
$globalVar = "I am global";

function testScope() {
    // Local variable
    $localVar = "I am local";
    echo "Inside function, localVar: $localVar\n";

    // Accessing global variable using 'global' keyword
    global $globalVar;
    echo "Inside function, globalVar: $globalVar\n";

    // Static variable
    static $staticVar = 0;
    $staticVar++;
    echo "Inside function, staticVar: $staticVar\n";
}

testScope();
testScope();

echo "Outside function, globalVar: $globalVar\n";

// The following will cause errors if uncommented, because $localVar and $staticVar are not accessible here
// echo $localVar;
// echo $staticVar;
?>

There are two useful variable types in PHP. Global variables, which are defined outside functions and accessed inside them using the global keyword, and static variables, which are defined inside functions with static and keep their value between calls.

Variable scope affects both the accessibility and the lifetime of variables in your PHP programs. Using the right scope helps you avoid unexpected behavior and keeps your code organized and secure.

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Sezione 1. Capitolo 4

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