Page 126 - DCAP404 _Object Oriented Programming

Unit 6: Constructors and Destructors

Notes

Notes Note that C++ selects one constructor by matching the signature of the method
being called. Also, once you define a constructor method, the default constructor is
overridden and is not available to the class. Therefore you must also define a constructor
method resembling the default constructor method having no parameters.

6.1.2 Destructor

When a program no longer needs an instantiated object it destroys it. If you do not supply a
destructor function, C++ supplies a default destructor for you, unknown to you. The program
uses the destructor to destroy the object for you.
When should you define your own destructor function? In many cases you do not need a destructor
function. However, if your class created dynamic objects, then you need to define your own
destructor in which you will delete the dynamic objects. This is because dynamic objects cannot
be deleted on their own. So, when the object is destroyed, the dynamic objects are deleted by the
destructor function you define.

Did u know? Should we explicitly call a destructor on a local variable?
No!

The destructor will get called again at the close } of the block in which the local was
created. This is a guarantee of the language; it happens automatically; there’s no way to
stop it from happening. But you can get really bad results from calling a destructor on the
same object a second time! Bang! You’re dead!
A destructor function has the same name as the class, and does not have a returned value.
However you must precede the destructor with the tilde sign, which is ~ .
The following code illustrates the use of a destructor against dynamic objects:
#include <iostream>
using namespace std;

class Calculator
{
public:
int *num1;
int *num2;

Calculator(int ident1, int ident2)
{
num1 = new int;
num2 = new int;

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