I have the following code:
#include <iostream>
class A {
private:
int a;
public:
void setA(int a_);
friend int B::getA();
};
class B : public A {
public:
int getA();
};
void A::setA(int a_) {
a = a_;
}
int B::getA() {
return a;
}
int main() {
B myB;
myB.setA(9);
std::cout << myB.getA()<< std::endl;
return 0;
}
Compiling with g++ yields:
friend.cpp:10:16: error: use of undeclared identifier 'B'
friend int B::getA();
My thinking is that when the compiler is going through the class A definition, it does not yet know about class B. Therefore, I can forward declare B to take care of this problem:
#include <iostream>
class B;
class A {
...
That doesn't quite work:
friend.cpp:10:16: error: incomplete type 'B' named in nested name specifier
friend int B::getA();
It looks like the compiler isn't able to resolve the function as it is given.
How can I make a derived class function a friend in the base class?
Your code seems to violate the basic concept of data encapsulation. To resolve it, either make A::a protected, as @rici suggested, or define a getter in class A.
class A {
private:
int a;
public:
void setA(int a_);
virtual int getA();
};
class B : public A {
public:
int getA();
};
void A::setA(int a_) {
a = a_;
}
int A::getA() {
return a;
}
int B::getA() {
return A::getA();
}
Collected from the Internet
Please contact [email protected] to delete if infringement.
Comments