C++ Tutorial
C++ Classes and Objects
The main
purpose of C++ programming is to add object orientation to the C programming
language and classes are the central feature of C++ that supports object-oriented
programming and are often called user-defined types.
A class is
used to specify the form of an object and it combines data representation and
methods for manipulating that data into one neat package. The data and
functions within a class are called members of the class.
C++ Class Definitions:
When you
define a class, you define a blueprint for a data type. This doesn't actually
define any data, but it does define what the class name means, that is, what an
object of the class will consist of and what operations can be performed on
such an object.
A class
definition starts with the keyword class followed by the class name; and the
class body, enclosed by a pair of curly braces. A class definition must be
followed either by a semicolon or a list of declarations. For example, we
defined the Box data type using the keyword class as follows:
class Box
{
public:
double length; // Length of a box
double breadth; // Breadth of a box
double height; // Height of a box
};
The keyword public determines the access attributes of
the members of the class that follow it. A public member can be accessed from
outside the class anywhere within the scope of the class object. You can also
specify the members of a class as private or protected which we will discuss in a
sub-section.
Define C++ Objects:
A class
provides the blueprints for objects, so basically an object is created from a
class. We declare objects of a class with exactly the same sort of declaration
that we declare variables of basic types. Following statements declare two
objects of class Box:
Box Box1; // Declare Box1 of type Box
Box Box2; // Declare Box2 of type Box
Both of
the objects Box1 and Box2 will have their own copy of data members.
Accessing the Data
Members:
The public
data members of objects of a class can be accessed using the direct member
access operator (.). Let us try the following example to make the things clear:
#include <iostream>
using namespace std;
class Box
{
public:
double length; // Length of a box
double breadth; // Breadth of a box
double height; // Height of a box
};
int main( )
{
Box Box1; // Declare Box1 of type Box
Box Box2; // Declare Box2 of type Box
double volume = 0.0; // Store the volume of a box here
// box 1 specification
Box1.height = 5.0;
Box1.length = 6.0;
Box1.breadth = 7.0;
// box 2 specification
Box2.height = 10.0;
Box2.length = 12.0;
Box2.breadth = 13.0;
// volume of box 1
volume = Box1.height * Box1.length * Box1.breadth;
cout << "Volume of Box1 : " << volume <<endl;
// volume of box 2
volume = Box2.height * Box2.length * Box2.breadth;
cout << "Volume of Box2 : " << volume <<endl;
return 0;
}
When the
above code is compiled and executed, it produces the following result:
Volume of Box1 : 210
Volume of Box2 : 1560
It is
important to note that private and protected members can not be accessed
directly using direct member access operator (.). We will learn how private and
protected members can be accessed.
Classes & Objects
in Detail:
So far,
you have got very basic idea about C++ Classes and Objects. There are further
interesting concepts related to C++ Classes and Objects which we will discuss
in various sub-sections listed below:
|
Concept
|
Description
|
|
Class member functions
|
A member function of a class is a function
that has its definition or its prototype within the class definition like any
other variable.
|
|
Class access modifiers
|
A class member can be defined as public,
private or protected. By default members would be assumed as private.
|
|
Constructor & destructor
|
A class constructor is a special function
in a class that is called when a new object of the class is created. A
destructor is also a special function which is called when created object is
deleted.
|
|
C++ copy constructor
|
The copy constructor is a constructor
which creates an object by initializing it with an object of the same class,
which has been created previously.
|
|
C++ friend functions
|
A friend function is permitted full access to
private and protected members of a class.
|
|
C++ inline functions
|
With an inline function, the compiler
tries to expand the code in the body of the function in place of a call to
the function.
|
|
The this pointer in C++
|
Every object has a special pointer this which points to the object itself.
|
|
Pointer to C++ classes
|
A pointer to a class is done exactly the
same way a pointer to a structure is. In fact a class is really just a
structure with functions in it.
|
|
Static members of a class
|
Both data members and function members of
a class can be declared as static
|
