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NOTE
Totally Immersed: C++ Classes and Object-Oriented Programming
The scope-resolution operator is required only when you have derived
and base class functions with the same name and the same function
signature. You can call a public or protected function of the base class
at any time without the need for the scope-resolution operator,
provided they aren’t overridden. For example, if you wanted to check
the status of the aircraft prior to takeoff, you could do something like
this:
void MilitaryPlane::TakeOff(int dir)
{
if (GetStatus() != ONRAMP) Land(); // gotta land first!
Airplane::TakeOff(dir);
// new code goes here
}
In this case, the GetStatus() function exists only in the base class, so
there is no need for the scope-resolution operator. In the case of the
Land() function, the MilitaryPlane version will be called because it has
the most immediate scope.
When you derive a class from another class, you must be sure to call the base class’s
constructor so that all ancestor classes are properly initialized. Calling the base class
constructor is done in the initializer list. Here’s how the constructor for MilitaryPlane might
look:
MilitaryPlane:: MilitaryPlane(char* _name)
: Airplane(_name, MILITARY) // call base class
{
// body of constructor
}
Be sure to call the base class constructor whenever you derive a class from a base class. Figure
4.1 illustrates the concept of inheritance.
Figure 4.1.
An example of
inheritance.
MilitaryFighter MilitaryCargo Airliner Commuter SingleEngine TwinEngine
F16
C130
Airplane
Commerical
MilitaryPlane Airplane
CivilianPlane
PrivatePlane CargoPlane
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