C++ OOP: Constructor Destructor

The class constructor:

A class constructor is a special member function of a class that is executed whenever we create neww objects of that class

A costructor will have exact same name as the class and it does not have any return type at all, not even void.Constructors can be very useful for setting initial values for certain member variables.

Following example wxpalins the concept of constructor:

#include<iostream>
using namespace std;

class Line
{
public:
    void setLength(double len);
    double getLength(void);
    Line();//This is the consructor

private:
    double length;

};

Line::Line(void)
{
    cout<<"Object is being created"<<endl;
}

void Line::setLength(double len)
{
    length=len;
}

double Line::getLength(void)
{
    return length;
}

int main()
{
    Line line;
    //set line length
    line.setLength(6.0);
    cout<<"Length of line: "<<line.getLength()<<endl;
    return 0;
}

Parameterized Constructor:

A default constructor does not have any parameter, but if you need, a constructor can have parameters.This helps yout to assign initial value to an object at the time of its creation as shown in the example:

#include<iostream>
using namespace std;

class Line{

public:
    void setLength(double len);
    double getLength(void);
    Line(double len); //this is the constructor

private:
    double length;
};

//member functions definitions including constructor

Line::Line(double len)
{
    cout<<"Object is being created, length= "<<len<<endl;
    length=len;
}

void Line::setLength(double len)
{
    length=len;
}

double Line::getLength(void)
{
    return length;
}

//Main function for the program
int main()
{
    Line line(10.0);

    //get initially set length.
    cout<<"Length of the line: "<<line.getLength()<<endl;
    //set line length again
    line.setLength(6.0);
    cout<<"Length of line: "<<line.getLength()<<endl;

    return 0;
}

Using Initialization Lists to Initialize Fields:

In case of parameterized constructor, you can use following syntax to initialize the fields:

Line::Line(double len):length(len)
{
    cout<<"Object is being created, length= "<<len<<endl;
}

Above syntax is equal to the following syntax:

Line::Line(double len)
{
    cout<<"Object is being created, length= "<<len<<endl;
    length=len;
}

If for a class C, you have multiple fields X,Y,Z etc. to be initialized, then can be use same syntax and separate the fields by comma as follows:

C::C(double a,double b,double c):X(a),Y(b),Z(c)
{
    
    ........
    
}

The class Destructor:

A destructor is a special member fucntion that is executed whenever an object of it’s class goes out of scope or whenever the delete expression is applied to a pointer to the object of that class.

A destructor will have exact same name as the class prefixed with a tilde(~) and it can neither return a value nor can it take any paramaters.Destructor can be very useful for releasing resources before coming out of the program liek

#include<iostream>

using namespace std;

class Line{
public:
    void setLength(double len);
    double getLength(void);

    Line();
    ~Line();

private:
    double length;
};

Line::Line(void)
{
    cout<<"Object is being createrd"<<endl;
}

Line::~Line(void)
{
    cout<<"Object is being deleted"<<endl;
}

void Line::setLength(double len){
length=len;
}

double Line::getLength(void)
{

    return length;
}

int main()
{
    Line line;
    //set line length

    line.setLength(6.66);

    cout<<"Length of line: "<<line.getLength()<<endl;

    return 0;
}