c++ - 在类外调用的私有(private)函数成员

Question

在下面的例子中，为什么 B::f() 被调用，即使它是私有(private)的？

我知道这个事实:在调用点使用用于表示调用成员函数的对象的表达式类型检查访问。

#include <iostream>

class A {
public:
  virtual void f() { std::cout << "virtual_function"; }
};

class B : public A {
private:
  void f() { std::cout << "private_function"; }
};

void C(A &g) { g.f(); }

int main() {
  B b;
  C(b);
}

Answer 1

因为标准是这样说的:

[C++11: 11.5/1]: The access rules (Clause 11) for a virtual function are determined by its declaration and are not affected by the rules for a function that later overrides it. [ Example:

class B {
public:
  virtual int f();
};
class D : public B {
private:
  int f();
};
void f() {
  D d;
  B* pb = &d;
  D* pd = &d;
  pb->f();       // OK: B::f() is public,
                 // D::f() is invoked
  pd->f();       // error: D::f() is private
}

—end example ]

这个例子和你的一样，哈哈。