Dynamic Constructor in C++

Dynamic constructors create dynamic memory by using a dynamic memory allocator new within the constructor. This allows us to initialize objects dynamically. The term dynamic constructor is used when memory allocation is done dynamically inside a constructor using the keyword new.

The dynamic constructor will not create any memory for the object. However, it creates a memory block that the objects could access.

Example-1:

#include<iostream>
using namespace std;


class example
{
  const char* ptr;


public:


  // default constructor
  example()
  {
    // allocating memory at run time by using the new keyword
    ptr = new char[15];
    ptr = "Hi from example constructor ";
  }


  void display()
  {
    cout << ptr;
  }
};


int main()
{
  example  obj1;
  obj1.display();
}

Output:

Explanation:

In the above example, we have created a class example inside which we have given a constructor with the same name as the class name. We have declared a pointer for a character. We have used the pointer and created a char using the pointer.

Example-2:

#include<iostream>
using namespace std;


class example
{
  int num1;
  int num2;
  int *ptr;


public:
  // default constructor (here, it is a dynamic constructor also)
  example()
  {
    num1 = 0;
    num2 = 0;
    ptr = new int;
  }


  //dynamic constructor with parameters
  example(int x, int y, int z)
  {
    num1 = x;
    num2 = y;


    ptr = new int;
    *ptr = z;
  }


 void display()
 {
   cout << num1 << " " << num2 << " " << *ptr;
 }
};


int main()
{
  example obj1;
  example obj2(20, 50, 1);


  obj1.display();
  cout << endl;


  obj2.display();
}

Output:

Explanation:

In the above example, we used the dynamic constructor and passed a few arguments. Unlike in the previous example, we have passed a few arguments.