C++ - Private Inheritance question

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Private Inheritance question

Hi I very recently did the C++ online Quiz and was surprised to find that my answer (1) to the following question (below) was incorrect. Is there something I am missing here, or is the answer incorrect. I thought this was the point of Private. "Always inaccessible regardless or derivation access".
Apparently (3) in the correct answer! according to the quiz!

The private member in derived class
1) Cannot be inherited
2) Can be inherited at all instances
3) Can be inherited only if the derived class is inheriting from base class with private access level
4) None of the Above

Total Answers and Comments: 5

Last Update: October 19, 2009 Asked by: BronzeBill

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Submitted by: charliearcuri

I think you are correct, BronzeBill. I just tried an experiment using MFC: ChildClass inheriting privately from ParentClass which has a private member - that private member is *not* accessible in a ChildClass method even though ChildClass : private BaseClass.

Above answer was rated as good by the following members:
zeal_goswami

September 02, 2008 19:46:06

charliearcuri

Member Since: September 2008 Contribution: 1

RE: Private Inheritance question

I think you are correct BronzeBill. I just tried an experiment using MFC: ChildClass inheriting privately from ParentClass which has a private member - that private member is *not* accessible in a ChildClass method even though ChildClass : private BaseClass.

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September 23, 2008 06:22:18

beharav

Member Since: September 2008 Contribution: 2

RE: Private Inheritance question

Your answer is right. Its 1. There is no way you can access a private member of a base class in the derived class by inheriting privately.

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September 26, 2008 07:34:11

gpuchtel

Member Since: September 2008 Contribution: 1

RE: Private Inheritance question

You are confusing inheritance with accessability. Private members are indeed inherited. That is there is a slot for it in the ‘vbtl’ when the class is constructed; however you don’t have access to it from a derived class unless the base class has made you a ‘friend’. If ‘private’ members were not inherited how would ‘friend(ship)’ work? So inheritance means ‘what do I (physically) get’ not ‘what can I (logically) see’.

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September 29, 2008 02:21:39

hrisheekesh.kale27

Member Since: September 2008 Contribution: 4

RE: Private Inheritance question

gpuchtel's answer makes sense to me. The fact that size of the derived class object is sum of size of all the public and private members of base class and derived class corroborates the argument.

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October 18, 2009 22:52:27

j_l_larson

Member Since: June 2008 Contribution: 4

RE: Private Inheritance question

You can if the base class provides public or protected methods that modify its private data. Then derived class can expose this using access specifiers.

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