C++ classes and objects | Program | My Cs Tutorial

Class in c++

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.

Classes and objects in c++ | My CS Tutorial

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 −

A class is an expanded concept of a data structure: instead of holding only data, it can hold both data and
functions.
An object is an instantiation of a class. In terms of variables, a class would be the type, and an object would be the variable.
Classes are generally declared using the keyword class, with the following format:-

class class_name {
access_specifier_1:
member1;
access_specifier_2:
member2;
...
} object_names;

example:-

class CRectangle {
int x, y;
public:
void set_values (int,int);
int area (void);
} rect;

The keyword public determines the access attributes of the members of the class that follows 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.

Example of C++ Class program

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.

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 −

Example of C++ objects program

#include <iostream>
using namespace std;
class CRectangle {
int x, y;
public:
void set_values (int,int);
int area () {return (x*y);}
};
void CRectangle::set_values (int a, int b) {
x = a;
y = b;
}
int main () {
CRectangle rect, rectb;
rect.set_values (3,4);
rectb.set_values (5,6);
cout << "rect area: " << rect.area() << endl;
cout << "rectb area: " << rectb.area() << endl;
return 0;
}

output:-

rect area: 12
rectb area: 30

It is important to note that private and protected members can not be accessed directly using direct member access operator (.).

Classes and 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

【1】 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.

【2】 Class Access Modifiers
A class member can be defined as public, private or protected. By default members would be assumed as private.

【3】 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.

【4】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.

【5】 Friend Functions
A friend function is permitted full access to private and protected members of a class.

【6】 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.

【7】 this Pointer
Every object has a special pointer this which points to the object itself.

【8】 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.

【9】 Static Members of a Class
Both data members and function members of a class can be declared as static.

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