C ++ Inheriting a private copy constructor: how does this not lead to a compile-time error?

Question

In C ++, if we have this class

class Uncopyable{
public:
    Uncopyable(){}
    ~Uncopyable(){}
private:
    Uncopyable(const Uncopyable&);
    Uncopyable& operator=(const Uncopyable&);
};

and then we have a derived class

class Dervied: private Uncopyable{
};

My question is: why doesn't this raise a compile-time error when the compiler generates a default copy constructor and assignment operators in a derived class? Does the non-generated code try to access the private members of the base class?

Answer 1

why doesn't this lead to a compilation error when the compiler generates a default copy constructor and assignment operators in a derived class?

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Answer 2

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Answer 3

++ 11 12.8/7 : " , ". Dervied . 12.8/11 :

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Answer 4

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Answer 5

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Derived Foo;
Derived Bar;
Foo = Bar

:

int GetAnswer(Derived bar)
    { /* Do something with a Derived */ }
Derived Foo;
int answer = GetAnser(Foo);

, foo GetAnswer.

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int GetAnswer(Derived& bar)
    { /* Do something with a Derived */ }
Derived Foo;
int answer = GetAnser(Foo);

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class uncreateable
{
    uncreateable() {}
  public:
    static int GetImportantAnswer();
};

Looking at this, you can see that I do not need to instantiate the class to call GetImportantAnswer (), but I could not create the instance if I wanted to. I could call this code using the following:

int answer;
answer = uncreateable::GetImportantAnswer();

Edit: spelling and grammar

Answer 6

Well, actually this program does not compile with g ++:

#include <iostream>
using namespace std;

class Uncopyable{
  public:
    Uncopyable(){}
    ~Uncopyable(){}
  private:
    Uncopyable(const Uncopyable&) {cout<<"in parent copy constructor";}
    Uncopyable& operator=(const Uncopyable&) { cout << "in parent assignment operator";}
};

class Derived: private Uncopyable{

};

int main() {
  Derived a;
  Derived b = a;
}

compiler output:

$ g++ 23183322.cpp 
23183322.cpp:10:88: warning: control reaches end of non-void function [-Wreturn-type]
    Uncopyable& operator=(const Uncopyable&) { cout << "in parent assignment operator";}
                                                                                       ^
23183322.cpp:13:7: error: base class 'Uncopyable' has private copy constructor
class Derived: private Uncopyable{
      ^
23183322.cpp:9:5: note: declared private here
    Uncopyable(const Uncopyable&) {cout<<"in parent copy constructor";}
    ^
23183322.cpp:19:15: note: implicit copy constructor for 'Derived' first required here
  Derived b = a;
              ^
1 warning and 1 error generated.