Tencent PHP programmer interview questions - summary of 15 magic methods

Function: Automatically load the file of the class when using the class on the current page
The parameter $className is the name of the class and can be customized
 */
function __autoload($className){
$className=strtolower($className);//It is best to add this step, because the class header Capital letters, some systems distinguish the case of file names
require("$className.class.php");//Load class files One.class.php Two.class.php and This file is in the same directory
echo '---------------------------------';//Test as a marker when calling
}
//Neither of the following two classes are defined in this file p>
$o=new One();//Use One class, initialize it
$t=new Two();//Use Two class, initialize it Initialization
?>

Note that if this function needs to be loaded normally, the file name needs to be set to the class name (lowercase recommended).class .php and other class names must have some relationship with the file name. In addition, if an exception occurs in this function and cannot be caught by Catch, Fatal Error will be displayed

2.__construct() constructor

In C# and PHP4, the function name of the constructor is the same as the class name. Of course, PHP5 also supports this (if the __construct method cannot be found, it will find the function name that is the same as the class name as the constructor). The reason why it is written like this The advantage is that if we want to change the name of the class, we only need to change the class name without changing the function name of the constructor. At the same time, it reduces the probability of making mistakes to some extent. Let's simply write the sample code!

class PcYoYo{
private $url;

$this->url=$url;
}
}
?>

3.__destruct() destructor

__destruct destructor method, PHP will call this method before the object is destroyed (that is, before it is cleared from memory)

By default, PHP only releases the memory occupied by object properties and destroys object-related resources.

Destructors allow you to execute arbitrary code to clear memory after using an object.

When PHP decides that your script is no longer associated with the object, the destructor will be called.

Within the namespace of a function, this will happen when the function returns.

For global variables, this happens at the end of the script. If you want to explicitly destroy an object, you can assign any other value to the variable pointing to the object. Usually assign the variable to NULL or call unset.

4.__call() is called when the called member method does not exist (or does not have permission) in the class. It is used to do some operations or prompt information after an error

//Initialize a class
class Person{
< ;p>private $name;
private $age;
private $sex;
function walk($hour ,$minute){
echo "$hour :$minute We will walk";
}

}
//Use the magic method __call
/*****
Function: Automatically call when the object calls a function that does not exist in the class to perform some operations
Parameters: $proName Name of the called function$ args parameter array $proName, $args are custom formal parameters that can be changed to suit your own style, but the meaning of these two parameters is fixed
***** /
function __call($proName,$args){

echo "The $proName doesn't exist! the parameters are";> ;
print_r($args);
echo '';
}

//Instantiate an object
$p=new Person();

$p->walk(5,39);
//Call a method that does not exist in the Person class Method
$p->work();//If the magic method __call is not used, an error occurs in the program and the error message is Fatal error: Call to undefined method Person::work( ) in D:/phpnow/htdocs/holiday/magic__call.php on line 29
//If the magic method __call is used, when the object calls a function that does not exist in the class, __call is Automatically called to perform certain operations.
?>

5.__clone()

This function is automatically called when an object is cloned. Its function is to perform some initialization operations on the cloned copy

//Initialize a class
class Computer{
< ;p>//
public $cpu='intel';
private $monitor;
private $keyboard ;
//Set the magic method __clone() function
function __clone(){//If you do not set this magic method, the clone will be exactly the same Yes, the __clone function is similar to the constructor of the class and performs some initialization operations
$this->cpu='AMD';//$this refers to the newly created clone object< ;/p>
}
//Set the destructor to compare the difference between = and clone
function __destruct(){
echo '******************************************< ;br>';
}
}// the end of the class
//Instantiate an object< ;/p>
$c1=new Computer();
//Use the reference method to add a reference, because the reference to the object is the stack memory stored in the memory In pointer terms, this means creating a pointer in the memory pointing to the object pointed to by $c1
//We can judge whether this is true by using the destructor Copied the object
$c2=$c1;
//Use the clone method to clone an object
$c3= clone $c1;
//Output the information comparison between the two
echo $c1->cpu,''; p>
echo $c3->cpu,'';
?>

6 .__get() When the member attribute called by the object is not declared or the level is private or protected, we can perform some of our own operations in this function

class Person{
private $name;
public $nation;
function __get($para){//There must be a parameter
echo $para.'Does not exist';
}
}
$p=new Person();
$name =$p->name;//call the __get function
$nation=$p->nation;//never call the __get function
? >

7.__set() This function is called when an undeclared or level is private or protected, etc., and we can perform some of our own operations in this function

class Pc{
private $key;
function __set($key,$value){//There must be two parameters. One is a member attribute and the other is a value
echo 'Assign value to '.$key.' .$value.'Failed';
}
}
$p=new Pc();
$p->key=123;
?>

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