PHP Variable Scope

• The scope of a variable determines it’s accessibility in the program to refer it.
• PHP has four different variable scopes:

1. Local
2. Global
3. Static
4. Parameter

Local Scope

• A variable declared within a PHP function is local and can only be accessed within that function.
• For example:

<?php
       $amt = 5000 ; // global scope
       
       function my_function()
       {
           echo $amt ;  // local scope
       }

?>

• The above script will not produce any output because the echo statement refers to the local scope variable $amt, which has not been assigned a value within that function.

• We can use local variables with the same name in different functions, because local variables are only recognized by the function in which they are declared.

• The scope of local variables is limited to that functions only in which they are declared and are deleted as soon as the function is over.

Global Scope

• Variables that are declared outside the functions have global scope.
• Global variables can be accessible from any part of the script that is not inside a function.
• To access a global variable from within a function, use the global keyword. For example:

<?php
      $x = 5;
      $y = 10;

      function sum()
      {
         global $x $y;
         $z = $x + $y;

         echo $z;
      }
      
      sum();

?>

• The above script will output 15.
• PHP also stores all global variables in $GLOBALS[index]  array.
• We can access individual variable by providing name of the variable as index.
• This global array is also accessible from within functions and can be used to update global variables directly.
• The previous example can be rewritten using $GLOBALS[] array as follow:

<?php
      $x = 5;
      $y = 10;

      function sum()
      {
         $z = $GLOBALS['x'] = $GLOBALS['y'];

         echo $z;
      }

      sum();
?>

Static Scope

• A soon as execution of a function is completed; all of its variables are deleted.
• In some cases you want a local variable not to be deleted.
• We can use the static keyword to achieve this while declaring the variable as follow:

static $my_static_var ;

• Each time the function is called, that variable will still have the data it contained the last time the function was invoked.
• Note: The variable is still local to the function.

Parameters

• A parameter is a local variable whose value is passed to the function at the time of function call.
• Parameters are also referred to as arguments.
• Parameters are declared in a parameter list as part of the function declaration as follow:

function func_name ($para1,$para2,...)
 {
    // function body
 }

• Parameters will be discussed in more detail while dealing with functions.