Access inner class private variable in outer class - c++

Question

//In file1.hpp
class A
{
protected:
class B
{
public:
B () {};
};
};
// In file2.hpp
class C
{
public:
void getValue()
{
D obj; ---- error: no matching function for call to D
printf("%d\n",obj.c);
}
class D : public A::B
{
friend class C; -- I tried writing this but still no luck.
public:
D(int a, int b) : c(a), d(b) {}
virtual ~D() {}
//something
private:
int c; int d;
};
class E : public D
{
E() : D(1,2) {}
virtual ~E() {}
};
}
int main()
{
C::E obj;
}
In the public function, getValue I want to access the private member variables of the class D which are (c and d). How can I do that? I tried putting "friend class C" inside class D and then tried creating an object of class D inside getValue function but instead of getting a value like c=5 or d=6, I always get 0.
If I print the value in the following area, I get the correct value. I won't be able to show you how getValue is called but just imagine that it is called somehow. I just need to print c,d in that.
D(int a, int b)
: c(a), d(b) {};
EDIT: At the time of instantiation in getValue, I do something like this
D obj; --- error: no matching function for call to D

Answer 1

Let take the following example:
#include <iostream>
//In file1.hpp
class A
{
protected:
class B
{
public:
B () = default;
};
friend class C; // <-- bad idea
};
// In file2.hpp
class C
{
public:
void getValue()
{
// Creating an object E?
E objE;
// Access c and d
std::cout << "c:" << objE.c << ", d:" << objE.d << std::endl;
}
class D : public A::B // <-- bad idea?
{
public:
D(int a, int b): c(a), d(b) {}
virtual ~D() {}
//something
private:
int c; // dangerous to not initialize basic types
int d;
friend class C; // <-- bad idea
};
class E : public D
{
public:
E() : D(1,2) {}
virtual ~E() {}
};
};
int main()
{
C objC;
objC.getValue();
}
( you can run it here: https://onlinegdb.com/hNfm7Pvg0f )
First is, to have an instance of E to access in C::getValue, so I instantiated an object.
private and protected indicate that those properties and methods are not available publicly (encapsulation) and that is exactly what you are trying to do. You can make exceptions with friend keyword, but that is rarely a good idea (I probably use it twice in my 20 years carrier). But hey! it works.