派生类拒绝访问基类受保护的成员 [英] Derived class denied access to base class protected members

问题描述

考虑以下课程：



类基数

{

受保护：

    int m_id;

};

class派生：公共基地

{

公开：

    static bool Foo（）

    {

        return offsetof（Base，m_id）> 0;

    }
};

Consider the following classes:

class Base
{
protected:
    int m_id;
};
class Derived : public Base
{
public:
    static bool Foo()
    {
        return offsetof(Base, m_id) > 0;
    }
};

此代码无法编译。   Visual Studio 2015抱怨静态派生的"Foo"功能。




错误C2248：'Base :: m_id'：无法访问"Base"类中声明的受保护成员

\ consoleapplication1.cpp（83）：注意：请参阅'Base :: m_id'的声明。



这对我没有意义。  我在派生类的静态成员函数中。  它是否应该无法引用基类的受保护成员？ 

This code does not compile.  Visual Studio 2015 complains about the static, derived "Foo" function.

error C2248: 'Base::m_id': cannot access protected member declared in class 'Base'
\consoleapplication1.cpp(83): note: see declaration of 'Base::m_id'

This makes no sense to me.  I am in a static member function of the derived class.  Should it not be able to refer to protected members of the base class? 

推荐答案

避免因偏移而产生的任何外来影响，我把Foo改为

To avoid any extraneous effects from offsetof, I changed Foo to

static int Foo()
    {
        return m_id;
    }

在这种情况下，VS2013报告了
"  2 智能感知：a非静态成员引用必须相对于特定对象"

"错误C2597：非法引用非静态成员'Base :: m_id'"

In this case, VS2013 reported
" 2 IntelliSense: a nonstatic member reference must be relative to a specific object"
"error C2597: illegal reference to non-static member 'Base::m_id'"

删除"静态"消除了错误。 这有助于您了解真正的问题吗？

Removing "static" eliminated the error.  Does this help you understand the real issue?

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