Encapsulation in C++

In normal terms Encapsulation is defined as wrapping up of data and information under a single unit. In Object Oriented Programming, Encapsulation is defined as binding together the data and the functions that manipulates them.
Consider a real life example of encapsulation, in a company there are different sections like the accounts section, finance section, sales section etc. The finance section handles all the financial transactions and keep records of all the data related to finance. Similarly the sales section handles all the sales related activities and keep records of all the sales. Now there may arise a situation when for some reason an official from finance section needs all the data about sales in a particular month. In this case, he is not allowed to directly access the data of sales section. He will first have to contact some other officer in the sales section and then request him to give the particular data. This is what encapsulation is. Here the data of sales section and the employees that can manipulate them are wrapped under a single name “sales section”.

Encapsulation also lead to data abstraction or hiding. As using encapsulation also hides the data. In the above example the data of any of the section like sales, finance or accounts is hidden from any other section.

In C++ encapsulation can be implemented using Class and access modifiers. Look at the below program:

// c++ program to explain 

// Encapsulation 

#include<iostream> 

using namespace std; 

class Encapsulation 

{ 

private: 

// data hidden from outside world 

int x; 

public: 

// function to set value of 

// variable x 

void set(int a) 

{ 

x =a; 

} 

// function to return value of 

// variable x 

int get() 

{ 

return x; 

} 

}; 

// main function 

int main() 

{ 

Encapsulation obj; 

obj.set(5); 

cout<<obj.get(); 

return 0; 

} 

output:

5

In the above program the variable x is made private. This variable can be accessed and manipulated only using the functions get() and set() which are present inside the class. Thus we can say that here, the variable x and the functions get() and set() are binded together which is nothing but encapsulation.

All C++ programs are composed of the following two fundamental elements −

• Program statements (code) − This is the part of a program that performs actions and they are called functions.
• Program data − The data is the information of the program which gets affected by the program functions.

Encapsulation is an Object Oriented Programming concept that binds together the data and functions that manipulate the data, and that keeps both safe from outside interference and misuse. Data encapsulation led to the important OOP concept of data hiding.

Data encapsulation is a mechanism of bundling the data, and the functions that use them and data abstraction is a mechanism of exposing only the interfaces and hiding the implementation details from the user.

C++ supports the properties of encapsulation and data hiding through the creation of user-defined types, called classes. We already have studied that a class can contain private, protected and public members. By default, all items defined in a class are private. For example −

class Box {
   public:
      double getVolume(void) {
         return length * breadth * height;
      }

   private:
      double length;      // Length of a box
      double breadth;     // Breadth of a box
      double height;      // Height of a box
};

The variables length, breadth, and height are private. This means that they can be accessed only by other members of the Box class, and not by any other part of your program. This is one way encapsulation is achieved.

To make parts of a class public (i.e., accessible to other parts of your program), you must declare them after the public keyword. All variables or functions defined after the public specifier are accessible by all other functions in your program.

Making one class a friend of another exposes the implementation details and reduces encapsulation. The ideal is to keep as many of the details of each class hidden from all other classes as possible.

Data Encapsulation Example

Any C++ program where you implement a class with public and private members is an example of data encapsulation and data abstraction. Consider the following example −

#include <iostream>
using namespace std;

class Adder {
   public:
      // constructor
      Adder(int i = 0) {
         total = i;
      }
      
      // interface to outside world
      void addNum(int number) {
         total += number;
      }
      
      // interface to outside world
      int getTotal() {
         return total;
      };
   
   private:
      // hidden data from outside world
      int total;
};

int main() {
   Adder a;
   
   a.addNum(10);
   a.addNum(20);
   a.addNum(30);

   cout << "Total " << a.getTotal() <<endl;
   return 0;
}

When the above code is compiled and executed, it produces the following result −

Total 60

Above class adds numbers together, and returns the sum. The public members addNum and getTotal are the interfaces to the outside world and a user needs to know them to use the class. The private member total is something that is hidden from the outside world, but is needed for the class to operate properly.

Designing Strategy

Most of us have learnt to make class members private by default unless we really need to expose them. That's just good encapsulation.

Role of access specifiers in encapsulation

As we have seen in above example, access specifiers plays an important role in implementing encapsulation in C++. The process of implementing encapsulation can be sub-divided into two steps:

1. The data members should be labeled as private using the private access specifiers
2. The member function which manipulates the data members should be labeled as public using the public access specifier

// c++ program to explain // Encapsulation    #include<iostream>