Difference between revisions of "Advanced-C++/C2/Constructor-And-Destructor/English"

Constructors

Types of constructors

Destructors.

We will do this with the help of some examples.

Ubuntu Operating System version 11.10,

g++ Compiler version 4.6.1.

A constructor is a member function.

It has the same name as the class name.

Constructors cannot return values.

It is automatically called when an object is created.

Types of Constructors are:

Parameterized Constructors.

Copy Constructors.

And

Default Constructors.

Let us move on to destructors.

Destructors are used to deallocate memory.

They are called when an object is destroyed.

A destructor takes no arguments and has no return types.

I have already typed the code on the editor,

I will open it.

constructor.cpp

In this program we will perform the addition of two numbers using constructor.

Let me explain the code now.

#include <iostream>

using namespace std;

class Addition

int a, b ;

These are the private members of class Addition.

public

Addition(int, int)

The constructor has the same name as the class name.

We have passed two arguements here.

int add( )

For this we use a tilde sign followed by the destructors name.

return(a + b);

It returns sum of a and b.

Addition :: Addition (int a, int b)

a and b are private members.

To access the private members we use x and y.

Then we access the destructor.

In this we print Memory Deallocation.

int main()

Addition obj (3, 4);

Then we pass two arguments as 3 and 4.

3 will be stored in x and 4 will be stored in y.

This means a's value is 3 and b's value is 4.

The constructor that has arguments is called parameterized constructor.

Hence this one is the prameterized constructor.

cout << “Sum is ” <<obj.add() <<“\n”

And we print the sum.

return 0;

Ctrl, Alt and T keys simultaneously

g++ const-dest.cpp -o cons

To execute

Type

./cons

g++ space cons-dest.cpp space -o space cons

Press Enter

To execute

Type

./cons

Press Enter

Output

Sum is 7.

And Memory Deallocation

Come back ot our program.

I have already typed the code.

Note that our filename is default.cpp

If a constructor is not declared in the class,

Then the compiler assumes a default constructor for the class.

This is our header file as iostream.

Highlight

class Subtraction

Then we have a and b declared as public.

int sub(int a, int b)

return (a-b);

We have passed two arguments int a and int b.

This returns the subtraction of two numbers a and b.

Subtraction ();

Here we access the default constructor using the scope resolution operator.

int main()

int x;

In this we have defined a variable x.

Subtraction s;

x=s.sub(8,4);

And pass two arguments as 8 and 4.

Then the result is stored in variable x.

cout <<"Difference is "<<x<<"\n";

return 0;

This is our return statement.

Come back to our terminal.

g++ default.cpp -o def

Type

./def

Type

g++ space default.cpp space -o space def

Press Enter

Type

./def

Press Enter

Output

Difference is 4

Come back to our program.

Here you can see that we have passed the arguments within the function.

And in our previous example we have passed the arguments within the Object.

And here we have passed the arguments using the Object.

Now let us go back to our slides.

In this tutorial we learned,

Constructors.

eg. Addition

Parameterized Constructor.

eg. Addition obj (3, 4);

Destructors

eg. ~Addition

Default Constructor.

eg. Subtraction

Create a class named Division.

Create a constructor for the class.

And

Create a function divide which divides two given numbers.

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