C++ calling base class constructors
The default class constructor is called unless you explicitly call another constructor in the derived class. the language specifies this.
Rectangle(int h,int w):
Shape(h,w)
{...}
Will call the other base class constructor.
The short answer for this is, "because that's what the C++ standard specifies".
Note that you can always specify a constructor that's different from the default, like so:
class Shape {
Shape() {...} //default constructor
Shape(int h, int w) {....} //some custom constructor
};
class Rectangle : public Shape {
Rectangle(int h, int w) : Shape(h, w) {...} //you can specify which base class constructor to call
}
The default constructor of the base class is called only if you don't specify which one to call.