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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.

What is the Constructor in C++?

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.

Why Constructor is Used?

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).

What are the Properties of Constructor?

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 of C++ Constructor

#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 C++ Constructors

Normally Constructors are following type:

1. Default Constructor or Zero argument constructor
2. Parameterized constructor
3. Copy constructor
4. Conversion constructor
5. Explicit constructor

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