Variable Scope

The scope of a variable is the context within which it is defined, and its value is available.

Global Scope

Any variable defined will be having

  1. a global scope in the file it is defined.
  2. and in the file included via include(), require(), include_once(), require_once()
<?php
#tea.php
$v = 100;

include 'sugar.php';

?>

<?php
#sugar.php

// Output wil be 100
echo $v
?>

Common use is as follows

config.php

We Store the config details once in config.php and include it whenever we want. In our example we are including in userdetails.php

Since PHP provides global scope to the included files we enjoy these kinds of patterns.

<?php
//config.php

// We declare the db config info in config.php and whenever we require that
// we include and the values can be accessed in the file it is included.
$db_host = 'localhost';
$db_name = 'students_db';
$db_username = 'prem';
$db_password = 'prem';


?>

userdetails.php

<?php
//Userdetails.php

include 'config.php';

//can use $db_host, $db_username, $db_password 
//Very useful usecase is possible because of the global scope.
$link = mysql_connect( $db_host, $db_username, $db_password )

if( !$link ){
    die('Could not connect: ' . mysql_error());
}

echo 'Connected successfully';
mysql_close($link);
?>

Function Scope

  1. Any variable defined inside the function are available only within the function where it defined.
  2. Variable defined outside the function will NOT be available within the function scope.
<?php

$person = 'Ramkumar';

sayHelloTo();

function sayHelloTo(){
    echo "Hello !" . $person;
}

?>

To use the globally scoped variable you need to use global keyword in the function where you wanted to use the variable.

<?php

$person = 'Ramkumar';

sayHelloTo();

function sayHelloTo(){
    //Note I am redclaring the same variable inside the function but now
    //with global keyword before variable $person.
    global $person;

    // output Hello ! Ramkumar
    echo "Hello !" . $person;
}

?>

Static Variable

  1. A static variable exists only in a local function scope,
  2. but it does not lose its value when program execution leaves this scope.

Consider the following example: 

// Lets make 10 Omlets using Static variable
<?php
exampleStatic( 10 );
exampleStatic( 10 );

function exampleStatic( $a ){
    static $i = 0;
    $i++;
    echo $i;
}

?>