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PHP Variable Scope

Variable scope is the part of a program where a variable can be used. Each function has its own scope for the variables made inside it.

A wall between scopes

The outside $city holds Oslo. The function makes its own $city with Bergen, and that local value prints inside the call.

<?php
$city = "Oslo";

function showCity() {
  $city = "Bergen";
  echo $city . "\n";
}

showCity();
echo $city . "\n";

Reaching out with global

The word global links the name $count inside bump to the outside $count. The function adds 1, and the new value prints after the call.

<?php
$count = 0;

function bump() {
  global $count;
  $count = $count + 1;
}

bump();
echo $count . "\n";

A static variable remembers

The static variable $n is set up on the first call only. Each call adds 1 and prints the kept value.

<?php
function counter() {
  static $n = 0;
  $n = $n + 1;
  echo $n . "\n";
}

counter();
counter();

Example

<?php
$theme = "light";

function useDark() {
  global $theme;
  $theme = "dark";
}

echo $theme . "\n";
useDark();
echo $theme . "\n";

Key points

  • A variable made inside a function lives only inside that function.
  • A variable inside a function is separate from an outside variable with the same name.
  • The global keyword links a name inside a function to the outside variable of that name.
  • A change made through global changes the outside variable.
  • A static variable keeps its value between calls to its function.
  • A static variable is set up only on the first call.

In this example, the outside variable $theme starts as light. The first print shows light. useDark links its $theme to the outside one with global and changes it to dark, so the last print shows dark.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Programiz PHP Compiler

Exercise

What does the static word do to a variable inside a function?