C++ Programming - OOPS Concepts - Discussion

constructor is called at the time of object creation.

#include<iostream>
using namespace std;
class A
{
public:
A()
{
cout<<"constructor"<<endl;
}
}
int main()
{
A b1;
}

A constructor is called at the time of declaration of an object.

class A {};
class C /* declaration of a class */
{
A a_; /* declaration of an object (but not definition) of type A */
};

will call the constructor of A?

The constructor is a special member function of a class which is called/invoked when the object is created. It has the same name as that of a class.

By default a constructor is immediately called as soon as an object is created.

Here is an example you can understand clearly :).

#include <iostream>

using namespace std;

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

private:
double length;
};

// Member functions definitions including constructor
Line::Line(void)
{
cout << "Object is being created" << endl;
}

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

double Line::getLength( void )
{
return length;
}
// Main function for the program
int main( )
{
Line line;

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

return 0;
}

When object is created automatically constructor is declared.

If constructor is not define in class, then it will be provided by JVM automatically.

A constructor is called at the time of initialization of an object and not at declaration.

Because object needs to construct class elements and create real world object.

Constructor is called as soon as the object is invoked.