不能调用基类保护函数？ [英] cannot call base class protected functions?

问题描述

我无法在我的基类中调用protected函数。为什么？它看起来像这样：

I cant call protected function in my base class. Why? It looks something like this:

class B : B2
{
public:
  virtual f1(B*)=0;
protected:
  virtual f2(B*) { codehere(); }
}
class D : public B
{
public:
  virtual f1(B*b) { return f2(b); }
protected:
  virtual f2(B*b) { return b->f2(this); }
}

在pmvc中我得到错误错误C2248：'name :: class： ：f2'：无法访问类'name :: class'中声明的受保护成员

In msvc I get the error error C2248: 'name::class::f2' : cannot access protected member declared in class 'name::class'

在gcc中我得到错误：'virtual int name :: class :: f2 '受到保护。

In gcc I get error: 'virtual int name::class::f2()' is protected.

为什么？我认为受保护成员的要点是为派生类调用。

Why is that? I thought the point of protected members is for derived classes to call.

推荐答案

受保护的成员函数只能在基类中调用或在其派生类中。你不能在你的班级外面打电话。外部调用意味着调用类类型变量的成员函数。

Protected member functions can only be called inside the base class or in its derived class. You cannot call them outside your class. Outside calling means calling a member function of a class-typed variable.

因此

virtual f1(B*b) { return f2(b); }

是确定的，因为f2对类本身进行操作。 （内部呼叫）

is ok, because f2 operates on the class itself. (called inside)

但

virtual f2(B*b) { return b->f2(this); }

无法编译，因为f2对b不是D类本身。 （外面）这是非法的。

won't compile, because f2 operates on b not the class D itself. (called outside) It's illegal.

要修复它，B :: f2应该是公开的。

To fix it B::f2 should be public.

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