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In PHP, any variable that can be accessed from anywhere in a PHP script is called as a global variable. If the variable is declared outside all the functions or classes in the script, it becomes a global variable.

While global variables can be accessed directly outside a function, they aren’t automatically available inside a function.

Key Points About Global Variables

Here are some key points to keep in mind about global variables −

• External classes or functions that are defined
• Accessible globally, but internal operations need particular handling
• Use the $GLOBALS array or the global keyword to access functions.

Example

In the script below, $name is global for the function sayhello().

<?php
   $name = "Amar";
   function sayhello() {
      echo "Hello " . $name;
   }
   sayhello();
?>

Output

However, the variable is not accessible inside the function. Hence, you will get an error message “Undefined variable $name”.

Hello 
PHP Warning: Undefined variable $name in /home/cg/root/93427/main.php on line 5

Example

To get access within a function, you need to use the “global” keyword before the variable.

<?php
   $name = "Amar";
   function sayhello() {
      GLOBAL $name;
      echo "Hello " . $name;
   }
   sayhello();
?>

Output

It will produce the following output −

Hello Amar

If a function accesses a global variable and modifies it, the modified value is available everywhere after the function call is completed.

Let us change the value of $name inside the sayhello() function and check its value after the function is called.

Example

Take a look at this following example −

<?php
   $name = "Amar";
   function sayhello() {
      GLOBAL $name;
      echo "Global variable name: $name" .PHP_EOL;
      $name = "Amarjyot";
      echo "Global variable name changed to: $name" .PHP_EOL;
   }
   sayhello();
   echo "Global variable name after function call: $name" .PHP_EOL;
?>

Output

It will produce the following output −

Global variable name: Amar
Global variable name changed to: Amarjyot
Global variable name after function call: Amarjyot

The $GLOBALS Array

PHP maintains an associative array named $GLOBALS that holds all the variables and their values declared in a global scope. The $GLOBALS array also stores many predefined variables called as superglobals, along with the user defined global variables.

Any of the global variables can also be accessed inside any function with the help of a regular syntax of accessing an arrow element. For example, the value of the global variable $name is given by $GLOBALS[“name”].

Example

In the following example, two global variable $x and $y are accessed inside the addition() function.

<?php
   $x = 10;
   $y = 20;

   function addition() {
      $z = $GLOBALS['x']+$GLOBALS['y'];
      echo "Addition: $z" .PHP_EOL;
   }
   addition();
?>

Output

It will produce the following output −

Addition: 30

Example

You can also add any local variable into the global scope by adding it in the $GLOBALS array. Let us add $z in the global scope.

<?php
   $x = 10;
   $y = 20;
   function addition() {
      $z = $GLOBALS['x']+$GLOBALS['y'];
      $GLOBALS['z'] = $z;
   }
   addition();
   echo "Now z is the global variable. Addition: $z" .PHP_EOL;
?>

Output

It will produce the following output −

Now z is the global variable. Addition: 30

Including One PHP Script in Another

You can include one PHP script in another. Variables declared in the included script are added in the global scope of the PHP script in which it is included.

Here is “a.php” file −

<?php
   include 'b.php';
   function addition() {
      $z = $GLOBALS['x']+$GLOBALS['y'];
      echo "Addition: $z" .PHP_EOL;
   }
   addition();
?>

It includes “b.php” that has the $x and $y variables, so they become the global variables for the addition() function in “a.php” script.

<?php
   $x = 10;
   $y = 20;
?>

Global variables are generally used while implementing singleton patterns, and accessing registers in embedded systems and also when a variable is being used by many functions.

Scope can be defined as the range of availability a variable has to the program in which it is declared. PHP variables can be one of four scope types −

• Local Variables
• Global Variables
• Static Variables
• Function Parameters

Local Variables

A variable declared in a function is considered local; that is, it can be referenced solely in that function. Any assignment outside of that function will be considered to be an entirely different variable from the one contained in the function. You cannot access them outside of the function.

Consider local variables as private notes. Only the author (function) can read them.

How Local Variables Work

When a function is called, PHP creates local variables. When the function ends, PHP deletes the variables. Local variables exist only during the function’s execution.

Example 1

Here is the example to show hwo the local variable work in PHP −

<?php
   $x = 4;
   
   function assignx () { 
      $x = 0;
      print "\$x inside function is $x. \n";
   }
   
   assignx();
   print "\$x outside of function is $x. \n";
?>

Output

This will produce the following result −

$x inside function is 0. 
$x outside of function is 4. 

Example 2

You can use local variables inside a loop also. So check how the local variables work in a for loop.

<?php
   function countToThree() {
      for ($i = 1; $i <= 3; $i++) {
         // Local variable
         echo $i . " "; 
      }
   }

   countToThree();
?>

Output

Following is the output of the above code −

1 2 3

Example 3

In this example, $age is a local variable inside the checkAge() function. The variable is only available inside the function you can’t access it from outside.

<?php
   function checkAge() {
      // Local variable
      $age = 20; 
      if ($age >= 18) {
         echo "You are an adult.";
      } else {
         echo "You are a minor.";
      }
   }

   checkAge(); 
?>

Output

Following is the output of the above code −

You are an adult.

Why Use Local Variables?

Here are some of the reasons why you should use local variables −

• Security: Local variables protect data within functions.
• Memory Management: After use, local variables are deleted to save memory.
• Avoid conflict: Local variables with the same name in different functions do not interact with each other.

Important Points to Keep in Mind

Understanding local variables is important to write PHP code that is secure, efficient, and clean. Here are some key points of local variables you should keep in mind −

• Local variables are defined inside a function.
• Only when the function is operating do they exist.
• When not in use, they are inaccessible.
• Many functions can use the same variable names without getting any issues.

Arrow functions were added in PHP 7.4 to make it easier and faster to write anonymous functions. Instead of the regular “function” term, you can now type “fn”. The new version simplifies your code, making it cleaner and more readable. Arrow functions are perfect for short, one-line functions because they automatically return the result without the need for an explicit return statement.

They also inherit variables from the parent scope, so you do not need to pass them separately. Overall, arrow functions are a fantastic addition to PHP, making it faster and easier to write small inline functions.

Here is the syntax for using the arrow functions in your code −

fn(argument_list)=> expr

Key Points About Arrow Functions

Arrow functions have some key points listed below that make them different from regular functions −

• There is only one expression after the “=>” symbol, and its value is the return value of the arrow function.
• The arrow function doesn’t have an explicit return statement.
• Like in the anonymous function, the arrow function is assigned to a variable for it to be called.

Basic Addition with Arrow Function

The following example demonstrates how you can use the arrow function in PHP −

<?php
   $add = fn ($a, $b) => $a + $b;

   $x = 10;
   $y = 20; 
   echo " x: $x y: $y Addition: " . $add($x, $y);
?>

It will produce the following output −

x: 10 y: 20 Addition: 30

Using the Arrow Function as a Callback Function

We can also use the arrow function as a callback function. Callback functions are used as one of the arguments of another function. The arrow function is executed on the fly and the value of the expression after “=>” becomes the argument of the parent function, which may be either a built-in or a user-defined function.

In this example, we use an arrow function inside usort() function, a built_in function that sorts an array by values using a user-defined comparison function.

<?php
   $arr = [10,3,70,21,54];
   usort ($arr, fn ($x , $y) => $x > $y);

   foreach ($arr as $x){
      echo $x . "\n";
   }
?>

It will produce the following output −

3
10
21
54
70

Accessing Variables from the Parent Scope

Arrow functions can automatically access variables from the parent scope. Unlike the anonymous functions, the “use” keyword is not necessary for it to act as a closure. When a variable used in the expression is defined in the parent scope, it will be implicitly captured by-value.

<?php
   $maxmarks=300;
   $percent=fn ($marks) => $marks*100/$maxmarks;

   $m = 250;
   echo "Marks = $m Percentage = ". $percent($m);
?>

It will produce the following output −

Marks = 250 Percentage = 83.333333333333

Nested Arrow Functions

Arrow functions capture variables by value automatically, even when nested.

In the following example, an arrow function is defined in the expression part of another arrow function.

<?php
   $z = 1;
   $fn = fn($x) => fn($y) => $x * $y + $z;
   $x = 5;
   $y = 10; 
   echo "x:$x y:$y \n";
   echo "Result of nested arrow functions: " . ($fn($x)($y));
?>

It will produce the following output −

x:5 y:10 
Result of nested arrow functions: 51

Filtering an Array with Arrow Functions

You can use arrow functions to filter elements in an array very easily. So here is the example below in which we are filtering out the even numbers and showing them in the output.

<?php
   $numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
   $evenNumbers = array_filter($numbers, fn($n) => $n % 2 === 0);

   foreach ($evenNumbers as $num) {
      echo $num . " ";
   }
?>

Output

Following is the output of the above code −

2 4 6 8 10

Transform an Array with array_map

Arrow functions are used to transform an array using array_map. In the following example, we are using array_map() function to change the array into a squared numbers array.

<?php
   $nums = [1, 2, 3, 4];
   $squared = array_map(fn($n) => $n * $n, $nums);

   print_r($squared);
?>

Output

Following is the output of the above code −

Array
(
   [0] => 1
   [1] => 4
   [2] => 9
   [3] => 16
)

Just like anonymous functions, the arrow function syntax allows arbitrary function signatures, including parameter and return types, default values, variadics, as well as by-reference passing and returning.

What are Anonymous Functions?

PHP allows defining anonymous functions. Normally, when we define a function in PHP, we usually provide it a name which is used to call the function whenever required. In contrast, an anonymous function is a function that doesnt have any name specified at the time of definition. Such a function is also called closure or lambda function.

Sometimes, you may want a function for one time use only. The most common use of anonymous functions is to create an inline callback function.

Anonymous functions are implemented using the Closure class. Closure is an anonymous function that closes over the environment in which it is defined.

Syntax

The syntax for defining an anonymous function is as follows −

$var=function($arg1,$arg2){return$val;};

Note that there is no function name between the function keyword and the opening parenthesis, and the fact that there is a semicolon after the function definition. This implies that anonymous function definitions are expressions. When assigned to a variable, the anonymous function can be called later using the variables name.

Example

Take a look at the following example −

<?php
   $add = function ($a, $b) {
      return "a:$a b:$b addition: " . $a+$b; 
   };
   echo $add(5,10);
?>

Output

It will produce the following output −

a:5 b:10 addition: 15

Anonymous Function as a Callback

Anonymous functions are often used as callbacks. Callback functions are used as one of the arguments of another function. An anonymous function is executed on the fly and its return value becomes the argument of the parent function, which may be either a built-in or a user-defined function.

Example

In this example, we use an anonymous function inside the usort() function, a built in function that sorts an array by values using a user-defined comparison function.

<?php
   $arr = [10,3,70,21,54];
   usort ($arr, function ($x , $y) {
      return $x > $y;
   });
   foreach ($arr as $x){
      echo $x . "\n";
   }
?>

Output

It will produce the following output −

3
10
21
54
70

Example

The following example uses an anonymous function to calculate the cumulative sum after successive numbers in an array. Here, we use the array_walk() function. This function applies a user defined function to each element in the array.

<?php
   $arr=array(1,2,3,4,5);
   array_walk($arr, function($n){
      $s=0;
      for($i=1;$i<=$n;$i++){
         $s+=$i;
      }
      echo "Number: $n Sum: $s". PHP_EOL;
   });
?>

Output

It will produce the following output −

Number: 1 Sum: 1
Number: 2 Sum: 3
Number: 3 Sum: 6
Number: 4 Sum: 10
Number: 5 Sum: 15

Anonymous Function as Closure

Closure is also an anonymous function that can access the variables outside its scope with the help of the “use” keyword.

Example

Take a look a the following example −

<?php
   $maxmarks=300;
   $percent=function ($marks) use ($maxmarks) {
      return $marks*100/$maxmarks;
   };
   $m = 250;
   echo "Marks = $m Percentage = ". $percent($m);
?>

Output

It will produce the following output −

Marks = 250 Percentage = 83.333333333333

Static Anonymous Functions

Anonymous functions can be declared statically. This stops the current class from being automatically connected to them. Objects may not be bound to them during runtime.

Example

Here in the below example we are trying to use $this inside a static anonymous function −

<?php
   class MyClass
   {
      function sayHello()
      {
         $myFunction = static function($name) {
               echo "Hello " . $name . "!";
         };

         $myFunction("Aryan");
      }
   }

   $obj = new MyClass();
   $obj->sayHello();

?>

Output

Following is the output of the above code −

Hello Aryan!

PHP is widely regarded as a weakly typed language. In PHP, you need not declare the type of a variable before assigning it any value. The PHP parser tries to cast the variables into compatible type as far as possible.

For example, if one of the values passed is a string representation of a number, and the second is a numeric variable, PHP casts the string variable to numeric in order to perform the addition operation.

Automatic Type Casting in Addition

PHP converts the string to a number to perform the addition operation. Take a look at the following example −

<?php
   function addition($x, $y) {
      echo "First number: $x Second number: $y Addition: " . $x+$y;
   }

   $x="10";
   $y=20;
   addition($x, $y);
?>

It will produce the following output −

First number: 10 Second number: 20 Addition: 30

Error by Adding Non-Numeric String to a Number

However, if $x in the above example is a string that doesn’t hold a valid numeric representation, then you will encounter an error.

<?php
   function addition($x, $y) {
      echo "First number: $x Second number: $y Addition: " . $x+$y;
   }
   $x="Hello";
   $y=20;
   addition($x, $y);
?>

It will produce the following output −

PHP Fatal error:  Uncaught TypeError: Unsupported operand 
types: string + int in hello.php:5

Type Hints

Type-hinting is supported from PHP 5.6 version onwards. It means you can explicitly state the expected type of a variable declared in your code. PHP allows you to type-hint function arguments, return values, and class properties. With this, it is possible to write more robust code.

Let us incorporate type-hinting in the addition function in the above program −

functionaddition(int$x,int$y){echo"First number: $x Second number: $y Addition: ".$x+$y;}

Note that by merely using the data types in the variable declarations doesn’t prevent the unmatched type exception raised, as PHP is a dynamically typed language. In other words, $x=”10″ and $y=20 will still result in the addition as 30, whereas $x=”Hello” makes the parser raise the error.

Example

<?php
   function addition($x, $y) {
      echo "First number: $x \n";
      echo "Second number: $y \n";
      echo "Addition: " . $x+$y . "\n\n";
   }

   $x=10;
   $y=20;
   addition($x, $y);

   $x="10";
   $y=20;
   addition($x, $y);

   $x="Hello";
   $y=20;
   addition($x, $y);
?>

It will produce the following output −

First number: 10 
Second number: 20 
Addition: 30

First number: 10 
Second number: 20 
Addition: 30

First number: Hello 
Second number: 20
PHP Fatal error:  Uncaught TypeError: Unsupported operand 
types: string + int in hello.php:5

Using strict_types

PHP can be made to impose stricter rules for type conversion, so that “10” is not implicitly converted to 10. This can be enforced by setting strict_types directive to 1 in a declare() statement.

The declare() statement must be the first statement in the PHP code, just after the “<?php” tag.

Example

Take a look at the following example −

<?php
   declare (strict_types=1);
   function addition(int $x, int $y) {
      echo "First number: $x Second number: $y Addition: " . $x+$y;
   }

   $x=10;
   $y=20;
   addition($x, $y);
?>

It will produce the following output −

First number: 10 Second number: 20 Addition: 30

Now, if $x is set to “10”, the implicit conversion won’t take place, resulting in the following error −

PHP Fatal error:  Uncaught TypeError: addition(): Argument #1 
($x) must be of type int, string given

From PHP 7 onwards, type-hinting support has been extended for function returns to prevent unexpected return values. You can type-hint the return values by adding the intended type after the parameter list prefixed with a colon (:) symbol.

Example

Let us add a type hint to the return value of the division() function below.

<?php
   declare (strict_types=1);
   function division(int $x, int $y) : int {
      return $x/$y;
   }

   $x=10;
   $y=20;
   $result = division($x, $y);
   echo "First number: $x Second number: $y Addition: " . $result;
?>

Because the function returns 0.5, which is not of int type (that is, the type hint used for the return value of the function), the following error is displayed −

Fatal error: Uncaught TypeError: division(): Return value must be 
of type int, float returned in hello.php:5

Benefits of PHP Strict Typing

Here are the benefits of using the strict typing in your code −

• Strict typing improves code reliability to ensure type safety, reducing the risk of runtime errors due by incorrect data types.
• Explicit type definitions improve code readability by making it self-explanatory and understandable.
• When developers understand the different sorts of variables, it is easier to change and update the code without creating new errors.

In PHP, the scope of a variable is the context within which it is defined and accessible to the extent in which it is accessible. Generally, a simple sequential PHP script that doesnt have any loop or a function etc., has a single scope. Any variable declared inside the “<?php” and “?>” tag is available throughout the program from the point of definition onwards.

Variable Scope Types

Based on the scope, a PHP variable can be any of these types −

• Local Variables
• Global Variables
• $GLOBALS Array
• Static Variables

A variable in a main script is also made available to any other script incorporated with include or require statements.

Using Local Variables

In the following example, a “test.php” script is included in the main script.

main.php

<?php
   $var=100;
   include "test.php";
?>

test.php

<?php
   echo "value of \$var in test.php : " . $var;
?>

When the main script is executed, it will display the following output −

value of $var in test.php : 100

However, when the script has a user defined function, any variable inside has a local scope. As a result, a variable defined inside a function can’t be accessed outside. Variables defined outside (above) the function have a global scope.

Using Global Variables

Take a look at the following example −

<?php
   // global variable   
   $var=100;   
   function myfunction() {
      // local variable
      $var1="Hello"; 	
      echo "var=$var  var1=$var1" . PHP_EOL;
   }
   myfunction();
   echo "var=$var  var1=$var1" . PHP_EOL; 
?>

Output

It will produce the following output −

var=  var1=Hello
var=100  var1=

PHP Warning:  Undefined variable $var in /home/cg/root/64504/main.php on line 5
PHP Warning:  Undefined variable $var1 in /home/cg/root/64504/main.php on line 8

Note that a global variable is not automatically available within the local scope of a function. Also, the variable inside a function is not accessible outside.

The ‘global’ Keyword

To enable access to a global variable inside local scope of a function, it should be explicitly done by using the “global” keyword.

Example

The PHP script is as follows −

<?php
   $a=10; 
   $b=20;
   echo "Global variables before function call: a = $a b = $b" . PHP_EOL;
   function myfunction() {
      global $a, $b;
      $c=($a+$b)/2;
      echo "inside function a = $a b = $b c = $c" . PHP_EOL;
      $a=$a+10;
   }
   myfunction();
   echo "Variables after function call: a = $a b = $b c = $c";
?>

Output

It will produce the following output −

Global variables before function call: a = 10 b = 20
inside function a = 10 b = 20 c = 15
Variables after function call: a = 20 b = 20 c = 
PHP Warning:  Undefined variable $c in /home/cg/root/48499/main.php on line 12

Global variables can now be processed inside the function. Moreover, any changes made to the global variables inside the function will be reflected in the global namespace.

Accessing Global Variables with $GLOBALS Array

PHP stores all the global variables in an associative array called $GLOBALS. The name and value of the variables form the key-value pair.

Example

In the following PHP script, $GLOBALS array is used to access global variables −

<?php
   $a=10; 
   $b=20;
   echo "Global variables before function call: a = $a b = $b" . PHP_EOL;

   function myfunction() {
      $c=($GLOBALS['a']+$GLOBALS['b'])/2;
      echo "c = $c" . PHP_EOL;
      $GLOBALS['a']+=10;
   }
   myfunction();
   echo "Variables after function call: a = $a b = $b c = $c";
?>

Output

It will produce the following output −

Global variables before function call: a = 10 b = 20
c = 15
PHP Warning:  Undefined variable $c in C:\xampp\htdocs\hello.php on line 12
Variables after function call: a = 20 b = 20 c =

Static Variable

A variable defined with static keyword is not initialized at every call to the function. Moreover, it retains its value of the previous call.

Example

Take a look at the following example −

<?php
   function myfunction() {
      static $x=0;
      echo "x = $x" . PHP_EOL;
      $x++;
   }
   for ($i=1; $i<=3; $i++) {
      echo "call to function :$i : ";
      myfunction();
   }
?>

Output

It will produce the following output −

call to function :1 : x = 0
call to function :2 : x = 1
call to function :3 : x = 2