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Saturday, May 24, 2008

Constructors & Destructors of a Class in PHP

Constructors & Destructors of a Class in PHP

[Please read Introduction to Classes in C++, Introduction to Constructor and Destructor Functions in C++ and Destructor Functions in (C++) in Detail to know more about Constructors and Destructors, even though from C++’s perspective, they are useful nonetheless.]

Constructors

A constructor is a special member function of a class which is called automatically when an object of the class is created. We can use it to perform useful initialization such as giving initial values to member variables etc.

Unlike C++, PHP’s constructors always have the name ‘__construct’ and they can be defined as:

    function __construct()
    {
        ...

    }

Prior to PHP Version 5, constructors used to have the same name as of the class (like in C++). Though PHP5 still understands constructors defined this way to be backward compatible, it is advisable to use the new form.

e.g.

class myclass
{
    function 
__construct()
    {
        echo 
"Constructor Invoked Automatically!!";
    }
}

$ob=new myclass;
//prints "Constructor Invoked Automatically!!"

Parameterized Constructors

Constructors may also be defined to take parameters just like a regular function. A typical parameterized constructor may be defined as below:

class myclass
{
    function 
__construct($arg)
    {
        echo 
"Constructor Invoked with Argument: $arg";
    }
}

And to create objects of such classes, we’d have to use the following way:

$ob=new myclass(3);

Constructors may be defined to take any number of arguments just like a regular function.

Destructors

The opposite of constructor is what we call a Destructor. As the name, it gets called when an object is destructed (goes out of scope).

Similar to constructors, a destructor may be defined as:

    function __destruct()
    {
        ...

    }

One thing to note here is, destructors CANNOT take parameters, which is quite obvious why.

Destructors may be used to close certain things such as files and MySQL connection which the object used.

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