What is the Constructor and its types in C++?

Learn: What is the constructor in C++ programming language? Types of constructors in C++, Explain constructors with examples.

Constructor is the special type of member function in C++ classes, which are automatically invoked when an object is being created. It is special because its name is same as the class name.

Constructor is used for:

To initialize data member of class: In the constructor member function (which will be declared by the programmer) we can initialize the default vales to the data members and they can be used further for processing.
To allocate memory for data member: Constructor can also be used to declare run time memory (dynamic memory for the data members).

There are following properties of constructor:

Constructor has the same name as the class name. It is case sensitive.
Constructor does not have return type.
We can overload constructor, it means we can create more than one constructor of class.
We can use default argument in constructor.
It must be public type.

Example:

#include <iostream>

using namespace std;

class Sample
{
	private:
		int X;
	public:
		//default constructor 
		Sample()
		{
			//data member initialization
			X=5;
		}

		void set(int a)
		{
			X = a;
		}

		void print()
		{
			cout<<"Value of X :  "<<X<<endl;
		}
};

int main()
{
	//Constructor called when object created
	Sample S; 

	S.print();
	//set new value
	S.set(10);
	S.print();

	return 0;
}

Output

Value of X :  5
Value of X :  10

Types of constructors in C++

Normally Constructors are following type:

Default Constructor or Zero argument constructor
Parameterized constructor
Copy constructor
Conversion constructor
Explicit constructor

Note:
If we do not create constructor in user define class. Then compiler automatically insert constructor with empty body in compiled code.