Easy tutorial for C / C ++ - class 4 (default values of constructor and destructor)

Easy tutorial for C / C ++ - class 4 (default values of constructor and destructor)

- Let's see how to give a constructor's default value in initialization with a constructor. When declaring a constructor within a class, you can supply a datatype and an initial value.

- Let's look at an example.

Example Code

#include <iostream>

#include <iomanip>

using namespace std;

class tClass{

   private :

     int Na;

     int Nb;

   public :

     tClass(int A = 1, int B = 2);

     void prn();

};

tClass::tClass(int A, int B){

    Na = A;

    Nb = B;

}

void tClass::prn(){

     cout << " Na = " << Na << ", Nb = " << Nb << endl ;

}

int main() {

     tClass x;

     cout << " x : " << endl ;

     x.prn();

     cout << endl ;

     tClass y(3);

     cout << " y : " << endl ;

     y.prn();

     cout << endl ;

     tClass z(4,5);

     cout << " z : " << endl ;

     z.prn();

     return 0;

}

- We created class 'tClass' and declared member variables 'Na, Nb'. We have created a constructor with two integer arguments. At this time, we gave 1 and 2 as initial values.

- You created object 'x' in main function. In this case, we created it without arguments. We then called the output function.

- When declaring object 'y', only one argument were given. ('tClass y (3); ') Let's call the function' prn () 'to check the result.

- Then, when declaring object 'z', two arguments were given. ('tClass z (4,5); ') Let's call the function' prn () 'to check the result.

results :

 x :

 Na = 1, Nb = 2

 y :

 Na = 3, Nb = 2

 z :

 Na = 4, Nb = 5

- For object 'x', you can see that the initial values of 1 and 2 of the constructor are output.

- For object 'y', only one initial value (3) is given. At this time, 3 is assigned to the member variable 'Na' and the member variable 'Nb' is assigned the initial value '2' of the constructor.

- In case of object 'z', initial values 4 and 5 at the time of object creation are assigned to member variables Na and Nb and output.

Destructor :

- A destructor (as the opposite of a constructor) is a special member function that is called when an object is destroyed and cleans up the object.

- The destructor is indicated by a tilde (~) before the class name. You can not specify a parameter and the data type of the return value.

ex)

Declaration of constructor : tClass ();

Declaration of destructor : ~ tClass ();

Definition of constructor : tClass :: tClass () {}

Definition of destructor : tClass :: ~ tClass () {}

- The C ++ compiler automatically calls the default destructor even if you do not explicitly describe the destructor. If you need to do something special when destroying an object, you should create a destructor and do something special.

ex) If you have been allocated memory space by dynamic memory allocation in the constructor, you need to deallocate memory allocated by the destructor.