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Parameterized constructor in C++ with example

Learn: What is the parameterized constructor in C++ programming language? How to create parameterized constructor to initialize data members of a class?

In our last two posts, we have covered following two topics, if you didn't read them, I would recommend to read them first, the covered topics are:

• What are the constructors in C++?
• What are the default or zero argument constructor in C++?

In this post, we are going to learn parameterized constructor in C++ programming.

What is Parameterized Constructor in C++?

As the name suggests it's a constructor with arguments/parameters, it follows all properties of the constructor and takes parameters to initialize the data.

For Example: If we want to initialize an object with some values while declaring it, we can do it creating parameterized constructors.

Let suppose there is a class named Person with two data members name and age, we can initialize the data members while creating the objects like this:

Person per1("Manikanth",21);
Person per2("Abhisekh", 19);

Example of Parameterized Constructor

Consider this example: Here Demo is a class with three private data members A, B and C

#include <iostream>
using namespace std;

class Demo {
 private:
  int A;
  int B;
  int C;

 public:
  // parameterized constructor
  Demo(int A, int B, int C);
  void set(int A, int B, int C);
  void print();
};

Demo::Demo(int A, int B, int C) {
  this->A = A;
  this->B = B;
  this->C = C;
}

void Demo::set(int A, int B, int C) {
  this->A = A;
  this->B = B;
  this->C = C;
}

void Demo::print() {
  cout << "Value of A :  " << A << endl;
  cout << "Value of B :  " << B << endl;
  cout << "Value of C :  " << C << endl;
}

int main() {
  // Parameterized Constructor called when object created
  Demo obj = Demo(1, 1, 1);
  // here, 1,1,1 will be assigned to A,B and C
  // printing the value
  obj.print();
  // changing the value using set function
  obj.set(10, 20, 30);
  // printing the values
  obj.print();

  return 0;
}

Output

Value of A :  1
Value of B :  1
Value of C :  1
Value of A :  10
Value of B :  20
Value of C :  30