Detailed explanation of the usage of php static static variable modifier

This article introduces the specific usage of the static variable modifier static in PHP, including some commonly used examples. Friends in need can refer to it.

php static variables only exist in the local function scope, but their values ​​are not lost when the program execution leaves this scope. Example:

<?php
/**
* php静态变量 函数应用
* edit bbs.it-home.org
*/
function test(){
static $a=0;
$a++;
echo $a;
}

test();//1
test();//2
test();//3
?>

Instructions: Assigning it with the result of an expression in a declaration will result in a parsing error.

static $a=0+1; static $a=sqrt(121);

The assignment method above will report an error.

The following is a detailed explanation of the usage of PHP static variables.

In PHP programming, another important feature about variable scope is static variables. Static variables only exist in the local function scope, but their values ​​are not lost when program execution leaves this scope.

Let’s first look at a simple example of php static variables:

<?PHP
   function Test(){
       $a = 0;
       echo $a;
       $a++;
   }
?>

This function is not very useful because it will set the value of $a to 0 and output "0" every time it is called. $a++, which increments a variable by one, has no effect because the variable $a no longer exists once this function exits. To write a counting function that does not lose the current count value, define the variable $a as static: Example:

<?PHP
//php静态变量的例子
   function Test(){
     static $a = 0;
     echo $a;
     $a++;
   }
?>

Now, each call to the Test() function will output the value of $a and increment it by one.

Static variables also provide a way to deal with recursive functions. A recursive function is a function that calls itself. Be careful when writing recursive functions, as they may recurse indefinitely. You must ensure that there are adequate ways to terminate recursion.

The following simple function recursively counts to 10, using the static variable $count to determine when to stop:

<?PHP
   function Test(){
       static $count = 0;
       $count++;
       echo $count;
       if ($count < 10) {
           Test();
       }
       $count--;
   }
?>

Note: Static variables can be declared as shown in the above example. Assigning it with the result of an expression in a declaration will result in a parsing error.

Look at this example of declaring a static variable:

<?PHP
//声明静态变量
   function foo(){
     static $int = 0;// correct
     static $int = 1+2;   // wrong (as it is an expression_r)
     static $int = sqrt(121); // wrong (as it is an expression_r too)
  
     $int++;
     echo $int;
   }
?>

That’s all about the static static variable modifier in PHP. I hope it will be helpful to everyone.