_php tutorial based on PHP5 Magic constants and Magic methods

Magic constants:
1. __line__
Returns the current line number in the file.
2. __file__
Returns the full path and file name of the file. If used in the include file, the include filename is returned. Since PHP4.0.2, __file__ always contains an absolute path, and the previous version sometimes contains a relative path.
3. __function__
Returns the function name (PHP4.3.0 new). Since PHP5 this constant returns the name (case-sensitive) when the function is defined. In PHP4, the value is always lowercase.
4. __class__
Returns the name of the class (PHP4.3.0 new addition). Since PHP5 this constant returns the name (case-sensitive) when the class is defined. In PHP4, the value is always lowercase.
5. __method__
Returns the method name of the class (PHP5.0.0). Returns the name of the method when it is defined (case-sensitive).
Magic Function:
1. __construct ()
Constructor: Called when an object is instantiated,
When a __construct and a constructor with a class name are present, __construct is called and the other is not called.
4. __get ()
When a property of an object is read, the property value is returned directly if the property exists, or the __get function is called if it does not exist.
5. __set ()
When you set the properties of an object,
If the attribute exists, the value is directly assigned;
If it does not exist, the __set function is called.
6. __tostring ()
Called when an object is printed. such as echo$obj; or print$obj;
7. __clone ()
Called when the object is cloned. such as: $t =newtest (); $t 1=clone $t;
8. __sleep ()
Serialize before being called. If the object is relatively large, want to cut a bit of the east and then serialize, you can consider this function.
9. __wakeup ()
Unserialize is called to do some initialization of the object.
10. __isset ()
Called when detecting whether an object's properties exist. such as: Isset ($c->name).
11. __unset ()
Called when a property of an object is unset. such as: unset ($c->name).
12. __set_state ()
Called when the Var_export is called. Use the return value of __set_state as the return value of Var_export.
13. __autoload ()
When an object is instantiated, the method is called if the corresponding class does not exist.

The method of first Knowledge magic
Php5.0 has provided us with a lot of object-oriented features since its release, especially for our easy-to-use magic methods that allow us to simplify our coding and better design our systems. Today we will come to know the Magic method that php5.0 offers us.
php| Magic Method |__tostring (), __clone (), __call (), __autoload () detailed
__tostring ()
If I have a class:
Classperson
{
Private $name = "";
Private $age = 0;
Function__construct ($name = "", $age = "")
{
$this->name = $name;
$this->age = $age;
}
Functionsay ()
{
echo "Name:" $this->name. "
”.” Age: ". $this->age."
”;
}
}
Now I'm going to instantiate this class and then print this example:
$p 1= New Person ("Liuzy", 20);
echo $p 1; Direct printing will make an error
It is obvious that this is an error to print directly to the object, because the object is a reference handle and cannot be printed directly. At this point, we can use the __tostring () method. We add a __tostring () method to the person class:
Function__tostring ()
{
Return "I am person,my name is". $this->name. "
”;
}
then refresh the page and find out what?
Now we understand that __tostring () is the method that executes when the object is printed directly, and we can use this method to print some information about the class.Note: There are two underscores, and the method must have a return value.
__clone ()
We know that objects can be directly assigned, such as
$p 2= $p 1; Here is an object with two references
Then I do:
$p 1->say ();
$p 2->say ();
Can be executed, and the effect is the same.

We also have a way to:
$p 3= clone $p 1; Note that clone is the Clone keyword, and the difference here is that $P3 is a new object.
At the same time we add a method to the class:
Function__clone ()
{
$this->name = "I am a copy"; Note: The $this here is the clone-generated object itself, not the current class
}
Then we execute:
$p 3->say ();
Print out:
Name: I am a copy
Age:20
Here we understand that the __clone () method is the method that executes when the object is cloned, and it acts as a property initialization for the newly cloned copy.
__call ()
The main function of this method is to execute the __call () method when an instance of the class calls a non-existent method. Note that you need to declare in the class in advance:
Function__call ($fname, $argus)
{
echo "The method you called:". $fname. " does not exist
”;
echo "parameter is". Print_r ($argus);
}
__autoload ()
When we call a class in peacetime, we must first introduce the file (include "xxx.php"), if we call a lot of classes in a page, then we have to use a lot of include "xxx.php". This is obviously a hassle.
The __autoload () method can help us solve this problem.

For example, we define the file that contains the person class above as person_class.php,
Create a new php file test.php, edit the content:
function __autoload ($calssName)
{
Include $className. " _class.php "; You see this, maybe you get it? Ha ha
}
$p = new Person ("Mifan", 22);
$p->say ();
This way the test.php page is executed without errors.
The __autoload () method is a method that is called when a class does not exist in life, and it has a string that declares the class name for the nonexistent class.
Of course, the name of the class file is also very fastidious. It's better to have a relationship with the class, like person_class.php.

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