What is the difference between the variable "GLOBAL" and "STATIC" in PHP?

Question

What is the difference between GLOBAL and STATIC variables in PHP? And which one is preferable to use when we want to use a variable in several functions?

Thanks.

Answer 1

A static variable simply means that var belongs to a class, but can be referenced without having to instantiate the specified class. The global var lives in the global namespace and can refer to any function in any class. Global vars have always frowned because they are so easily abused, overwritten, accidentally referenced, etc. At least with static vars you need to be referenced through Class::var;

Answer 2

Global is used to obtain global vars, which may be defined in other scenarios, or not in the same area.

eg.

 <?php $g_var = 1; function test() { var_dump($GLOBAL['g_var']); global $g_var; var_dump($g_var); } 

Static is used to define var, which has the entire script resource, and init only once.

eg.

 <?php function test() { static $cnt = 0; $cnt ++; echo $cnt; } $i = 10; while (-- $i) { test(); } 

Answer 3

A global variable is created before the function is created, but a global keyword is added to the function

 $g_var = 1; function test() { var_dump($GLOBAL['g_var']); global $g_var; var_dump($g_var); } 

static is created and declared static in the function

 function test() { static $cnt = 0; $cnt ++; echo $cnt; } $i = 10; while(--$i) test(); 

Answer 4

A global variable is a variable that is defined in scope and can cover the included and required areas. (Simply put, I mean php file / function / class)

Here are some examples of how global variables work.

Example 1: a variable declared in scope and used in a function using the global

 <?php $a = 1; function add_a() { global $a; $a++; } add_a(); echo $a; 

In the above example, we declare the variable $a and assign it a value of 1 in scope. Then we declare the add_a function in the same scope and try to increase the value of the variable $a . The add_a function is add_a , and then we echo $a variable, expecting the result to display 2 .

Example 2: a variable declared in scope and used in a function using the $GLOBALS variable

 <?php $a = 1; function add_a() { $GLOBALS['a']++; } add_a(); echo $a; 

The result from Example 2 above is exactly the same as the result from Example 1.

There is no difference in using the global and the PHP special variable defined in the $GLOBALS array. However, both of them have their advantages and disadvantages.

Learn more about $GLOBALS on the official PHP site $ GLOBALS

If you want to cover the declared scope variable with the included or required scope, see the example below.

Example 3: a.php file

 <?php global $a; $a = 1; require 'b.php'; add_a(); echo $a; 

b.php file

 <?php function add_a() { global $a; $a++; } 

In the above example, we have a.php and b.php . The b.php file b.php required in the a.php file because we use the function declared in the b.php file. To use the $a variable in the b.php file, we must first declare $a as global for use outside the local scope, and we will do this by first calling global $a , and then we define a value, for example, $a = 1 . The $ a variable is now available for use anywhere on any included areas, by first invoking global $a before manipulation.

Static variables Usually found in classes, but in some well-designed PHP projects you can find them in recursive functions. A static variable is a variable that remembers its value and can be reused every time a function or method is called.

Here are some examples of using a static variable.

Example 1: Static Variable in a Function

 function add() { static $a = 1; $a++; echo $a; } add(); //2 add(); //3 add(); //4 

Example 2: Static variable in a class

 class A { public static $a = 1; public static function add() { self::$a++; echo self::$a; } } echo A::$a; //1 A::add(); //2 echo A::$a; //2 A::add(); //3 echo A::$a; //3 A::add(); //4 

Note that you cannot assign a return value from a function to a static variable. For example, you cannot do static $a = rand() . See example 3 below on how to assign a return value to a static variable.

Example 3: Assigning a returned variable from a function to a static variable

 function add() { static $a; $a = rand(); echo $a; } 

Learn more about global and static variables on the official PHP website. Scope of variables