What are the 2 ways to destroy variables in php

Two methods for PHP to destroy variables: 1. Use the unset() function, the syntax "unset($varname)"; 2. Assign the value to the specified variable as "NULL", the syntax "$varname=null;" .

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

PHP variables or The destruction of objects can be divided into explicit destruction and implicit destruction:

1. Explicit destruction. When the object is not referenced, it will be destroyed, so we can unset or assign NULL to it;

2. Implicit destruction. PHP is a scripting language. When the last line of code is executed, all applied memory must be released.

Therefore, there are two ways to destroy variables. ：

• unset()

• ##$varname=null

For example:

class Human { 
  public $name = '张三'; 
  public $gender = null; 
  public function __destruct() { 
      echo &#39;死了!<br />&#39;; 
  } 
} 
$a = new Human(); 
$b = $c = $d = $a;
unset($a);
$d=null;


echo &#39;<hr />&#39;;
var_dump($a);
echo &#39;<hr />&#39;;
var_dump($b);
echo &#39;<hr />&#39;;
var_dump($c);
echo &#39;<hr />&#39;;
var_dump($d);

Notice: Undefined variable: a in /Library/WebServer/Documents/test.php on line 42
NULL
object(Human)#1 (2) { ["name"]=> string(6) "张三" ["gender"]=> NULL }
object(Human)#1 (2) { ["name"]=> string(6) "张三" ["gender"]=> NULL }
NULL 死了!

<?php
$a = 1;
$b = &$a;
unset($a);
var_dump($a); 
var_dump($b);

Notice: Undefined variable: a in E:\amp\apache\htdocs\index.php on line 5
NULL int(1)

$varname=null, the variable name still exists, but the memory value has been deleted. So what about in the case of pass-by-reference? Example:

<?php        
$a = 1;        
$b = &$a;        
$a=null;        
var_dump($a);        
var_dump($b);

NULL NULL

$varname=null, although the variable name and memory pointer still exist, the value in the memory is Completely deleted.

PHP Video Tutorial"

The above is the detailed content of What are the 2 ways to destroy variables in php. For more information, please follow other related articles on the PHP Chinese website!