PHP magic method: __construct __destruct

From php5 and later versions, classes can use magic methods. PHP stipulates that methods starting with two underscores (__) are reserved as magic methods, so it is recommended that function names do not start with __ unless it is to overload existing magic methods.

The existing magic methods in PHP include __construct, __destruct, __call, __get, __set, __isset, __unset, __sleep, __wakeup, __toString, __set_state and __clone.

This section will talk about __construct, __destruct:

__construct() - This method is called every time a new object is created

__destruct() - Executed when all references to the object are deleted or when the object is explicitly destroyed

<?php

/**
 * 清晰的认识__construct() __destruct
 */
class Example {

    public static $link;
    //在类实例化的时候自动加载__construct这个方法
    public function __construct($localhost, $username, $password, $db) {
        self::$link = mysql_connect($localhost, $username, $password);
        if (mysql_errno()) {
            die('错误:' . mysql_error());
        }
        mysql_set_charset('utf8');
        mysql_select_db($db);
    }

    /**
     * 通过__construct链接好数据库然后执行sql语句......
     */
    
    //当类需要被删除或者销毁这个类的时候自动加载__destruct这个方法
    public function __destruct() {
        echo '<pre class="brush:php;toolbar:false">';
        var_dump(self::$link);
        mysql_close(self::$link);
        var_dump(self::$link);
    }

}

$mysql = new Example('localhost', 'root', 'root', 'test');

result:

resource(2) of type (mysql link)
resource(2) of type (Unknown)

The above introduces the PHP magic method: __construct __destruct, including the content of PHP magic method. I hope it will be helpful to friends who are interested in PHP tutorials.