php中魔术方法是什么

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类中的魔术方法

PHP 魔术方法指的是在某些时刻会自动被调用的内置函数，它们以两个连续的下划线开头。

类中的魔术方法

__construct()

类的构造函数，用于初始化对象，在对象实例化时自动运行

__destruct()

析构函数，用于在 php 运行终止时，释放对象所占用的内存。析构函数是 php 的垃圾回收机制，使用栈结构，后进先出。

构造函数和析构函数的例子

class computer{    private $brand;    function __construct($brand){        $this->brand = $brand;    }    function __destruct(){        echo "release ".$this->brand."
";    }}$myComputer = new computer("MAC");$yourComputer = new computer("Asus");$hisComputer = new computer("Dell");echo "end of php file
";

输出结果如下所示

end of php filerelease Dellrelease Asusrelease MAC

可以发现析构函数在 php 文件执行结束之后才执行

__get($name)

类中用 protected 和 private 关键字定义的成员属性或方法是无法通过对象的实例访问的。__get() 方法会且仅会在对象的实例访问 proctected 和 private 成员属性 时自动执行 (访问成员方法时不会，因为没有意义)。

__get() 方法的意义在于将 proctected 和 private 成员属性进行处理后输出。

__get() 有且仅有一个输入参数

__get() 方法的一个例子

class computer{    private $brand;    protected $owner;    public $price;    function __construct($brand, $owner, $price){        $this->brand = $brand;        $this->owner = $owner;        $this->price = $price;    }    function __get($name){        echo "It's up to me to decide if let you konw the owner and the brand of this computer or not :)
";        echo "I will tell you the name of woner: ".$this->owner."
";        echo "I won't tell you that the brand is ".md5($this->brand)."
";        echo "
";    }    function __destruct(){        echo "release ".$this->brand."
";    }}$myComputer = new computer("MAC", "me", "1000");$yourComputer = new computer("Asus", "you", "500");$hisComputer = new computer("Dell", "his", "700");echo $myComputer->price; echo "

";echo $myComputer->owner;echo $yourComputer->brand;echo "end of php file
";

输出如下

1000It's up to me to decide if let you konw the owner and the brand of this computer or not :)I will tell you the name of woner: meI won't tell you that the brand is 2e25c285356cbb0ed8785a1377027d79It's up to me to decide if let you konw the owner and the brand of this computer or not :)I will tell you the name of woner: youI won't tell you that the brand is cb6ab3315634a1e4d11b091ba48b60baend of php filerelease Dellrelease Asusrelease MAC

可以看到，当访问 public 成员属性 price 时，__get()方法并没有被调用。输出 brand 时，我们使用了 md5 对其进行了加密处理，这种对封装的成员属性进行处理后输出的用法就是 get 方法的意义所在。

__set($name, $value)

__set($name, $value) 与用于给当前类中封装的方法或属性进行重新赋值或定义。

与 get 类似但不同的时，__set($name, $value)会在成员属性被访问赋值时自动执行，其中 $name 是被访问的成员属性名，$value 为成员属性被赋予的值

__set() 的例子

class computer{    private $brand;    protected $owner;    function __construct($brand, $owner, $price){        $this->brand = $brand;        $this->owner = $owner;        $this->price = $price;    }    function __get($name){        echo "It's up to me to decide if let you konw the owner and the brand of this computer or not :)
";        echo "I will tell you the name of woner: ".$this->owner."
";        echo "I won't tell you that the brand is ".md5($this->brand)."
";        echo "
";    }    function __set($name, $value){        $this->owner = $value;        echo "set $name to $value"."

";    }    function __destruct(){        echo "release ".$this->brand."
";    }}$myComputer = new computer("MAC", "me", "1000");echo $myComputer->owner = "my friend";echo $myComputer->owner;echo "end of php file
";

输出结果

set owner to my friendmy friendIt's up to me to decide if let you konw the owner and the brand of this computer or not :)I will tell you the name of woner: my friendI won't tell you that the brand is 2e25c285356cbb0ed8785a1377027d79end of php filerelease MAC

我们看到在给 owner 赋值时调用了 set , 而访问属性时，调用了 get 。

__tostring()

用于直接打印对象句柄，也就是说当我们使用 echo 加对象名时，__torsring()将会被自动调用

__tosring() 例子

class computer{    function __tostring(){        return "This is a computer class";    }}$myComputer = new computer();echo $myComputer;

如果没有 __totring() 方法，我们是无法使用 echo+对象名，会出现 fatal error

__call($method, $arguments)

当我们调用不存在的方法时，__call() 会自动执行，用于进行异常处理，并使程序继续正常运行。

__call() 例子

class computer{    function start(){        echo "starting computer
";    }    function __call($m, $a){        echo "erro function: ".$m;        echo "
";        echo "error param: ";        print_r($a);        echo "
";    }}$myComputer = new computer();$myComputer->start();$myComputer->shutdown('10 min', '20 min');echo "here";

输出结果为

starting computererro function: shutdownerror param: Array ( [0] => 10 min [1] => 20 min ) here

我们可以看到，$method 返回了错误的函数名，而 arguments 返回了参数，最后输出了 "here" 说明程序继续正常运行。

__clone() 方法 和 clone 关键字

clone 关键字用于复制对象，__clone() 方法实在克隆对象时自动调用的函数

clone 例子

class computer{    public $name;    function __clone(){        echo "A computer has been cloned
";    }}$myComputer = new computer();$youComputer = $myComputer;$youComputer->name = 'pc1';echo "My computer's name is ".$myComputer->name."
";echo "
";$hisComputer = clone $myComputer;$hisComputer->name = 'pc2';echo "My computer's name is ".$myComputer->name."
";echo "His computer's name is ".$hisComputer->name."
";

输出结果

My computer's name is pc1A computer has been clonedMy computer's name is pc1His computer's name is pc2

我们看到用 = 号并不能复制对象，只是为对象添加了一个别名而已，这里 $myComputer 和 $youComputer 指向同一块内存，修改了 $youComputer 的值相当于修改了 $myComputer 的值。

__autolaod()

在实例化对象时，__autolaod() 会自动被调用，用于快速取得对应的类文件

__autoload() 例子

带 try, catch 异常处理的例子

function __autoload($class_name){    echo "want to load ".$class_name."
";    if(file_exists($class_name.".class.php")){        include($class_name.".class.php");    }else{        throw new Exception("Unable to laod ".$class_name.".class.php");    }}try{    $obj = new myClass();}catch(Exception $e){    echo $e->getMessage()."
";}

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