A class in C++ is an encapsulation of data members and functions that manipulate the data. The class can also have some other important members which are architecturally important.
This C++ Tutorial discusses the components of a C++ class. More C++ tutorials will follow.
C++ Tutorial – Class Data Members:
Very important point about the Data members in this C++ Tutorial! This title is not a keyword or a data type in C++. This is just to explain one of the logical classifications of the types of members that are available in C++.
The data members can be of any legal data type, a class type, a struct type etc., They can also be declared as pointers and accessible normally as like other data members. The Example class given below in this C++ tutorial has two data members x and y of type integer.
C++ Tutorial – Function members in classes:
Functions declared inside a class can be any of the following four types. This C++ Tutorial explains each one of them as below.
Ordinary member functions :
These are ordinary functions defined with a return type and parameters. The return type can also be void. The special trait about member functions is they can access the private/protected data members of their class and manipulate them. No external functions can access the private/protected data members of a class. The sample below this C++ Tutorial uses an ordinary member function Add(), returning an integer value.
Constructors:
Constructors in C++ are special member functions of a class. They have the same name as the Class Name. There can be any number of overloaded constructors inside a class, provided they have a different set of parameters. There are some important qualities for a constructor to be noted.
- Constructors have the same name as the class.
- Constructors do not return any values
- Constructors are invoked first when a class is initialized. Any initializations for the class members, memory allocations are done at the constructor.
In the example class given below in this C++ tutorial has the constructor Example_Class(), with the same name as the class.
Destructors:
Destructors in C++ also have the same name, except for the fact that they are preceded by a ‘~’ operator. The destructors are called when the object of a class goes out of scope. It is not necessary to declare a constructor or a destructor inside a class. If not declared, the compiler will automatically create a default one for each. If the constructor/destructor is declared as private, then the class cannot be instantiated. Check below for the sample class of the C++ tutorial for an example of destructor.
C++ Tutorial – Access Level:
The classes in C++ have 3 important access levels. They are Private, Public and Protected. The explanations are as follows.
Private:
The members are accessible only by the member functions or friend functions.
Protected:
These members are accessible by the member functions of the class and the classes which are derived from this class.
Public:
Accessible by any external member. Look at the sample class below.
C++ Tutorial – Example of a class:
class Example_class //Sample Class for the C++ Tutorial
{
private:
int x; //Data member
int y; // Data member
public:
Example_Class() //Constructor for the C++ tutorial
{
x = 0;
y = 0;
}
~Example_Class() //destructor for the C++ Tutorial
{ }
int Add()
{
return x+y;
}
};