c++ - 使用 protected 和继承时无法访问在类中声明的私有(private)成员

Question

我在使用 protected 时遇到了一些问题成员。相关代码和我得到的错误如下。这些类具有所有需要的函数和变量。我刚刚总结了相关部分。我该怎么办 ？

MFS.h:

class MFS
{
protected:
    MatrixXd commandedLateral;
};

CSimulator.h:

class CSimulator : MFS
{
};

CSimulator.cpp:

void CSimulator::calculateActuator(MFS* mfs)
{
    actuator = -gain * mfs->commandedLateral(1,0);
}

错误 C2248:“MFS::commandedLateral”:无法访问在类“MFS”中声明的私有(private)成员

Answer 1

protected 成员只能通过派生类访问，即不能通过基类访问它 MFS .

(强调我的)

A protected member of a class is only accessible

1) to the members and friends of that class;

2) to the members and friends (until C++17) of any derived class of that class, but only when the class of the object through which the protected member is accessed is that derived class or a derived class of that derived class:

例如下面的代码应该可以正常工作。

void CSimulator::calculateActuator(CSimulator* mfs)
{
    actuator = -gain * mfs->commandedLateral(1,0);
}