C++ - When to use public, protected, private inheritance

See also:

public inheritance models an is-a relationship.


  class CDog : public CMammal { };

A dog is a mammal.

Use public to inherit base class implementation and interface. Public members of the base (it's interface) are public in the derived.
A derived class object can be used anywhere a base class object is expected (because derived is a base).

protected inheritance models an is-implemented-using relationship.


  class CCar : protected CAccelerator, protected CBrake, protected CClutch { };

A car is implemented using an accelerator, a brake, a clutch, etc., and we DO want to expose these subcomponents to subclasses of car.

Use protected to inherit base class implementation only. Public members of the base (it's interface) become protected in the derived.
Protected inheritance exposes implementation to subclasses of derived.

private inheritance models an is-implemented-using relationship.


  class CCar : private CAccelerator, private CBrake, private CClutch { };

A car is implemented using an accelerator, a brake, a clutch, etc., and we DON'T want to expose these subcomponents to subclasses of car.

Use private to inherit base class implementation only. Public members of the base (it's interface) become private in the derived.
Private inheritance hides implementation from subclasses of dervied.

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