受保护的成员只能由类的后代和同一模块中的代码访问。私有成员只能被声明它们的类以及同一模块中的代码访问。

当然，朋友函数把这个扔出窗外，但是。

私有成员只能在定义它们的类中访问。

可在定义受保护成员的类中以及从该类继承的类中访问受保护成员。

编辑:两者都可以被其类的友元访问，如果是受保护成员，则可以被其派生类的友元访问。

编辑2:使用任何在你的问题上下文中有意义的东西。您应该尽可能地将成员设为private，以减少耦合并保护基类的实现，但如果不可能，则使用受保护的成员。查看c++常见问题以更好地理解这个问题。这个关于受保护变量的问题可能也有帮助。

由于不需要公共成员函数来获取和更新派生类中的受保护成员，这提高了代码的效率，并减少了需要编写的代码量。然而，派生类的程序员应该知道他在做什么。

受保护的非静态基类成员可以被派生自该基类的任何类的成员和友元访问，方法是使用以下方法之一:

指向直接或间接派生类的指针 对直接或间接派生类的引用 直接或间接派生类的对象

The protected keyword specifies access to class members in the member-list up to the next access specifier (public or private) or the end of the class definition. Class members declared as protected can be used only by the following: Member functions of the class that originally declared these members. Friends of the class that originally declared these members. Classes derived with public or protected access from the class that originally declared these members. Direct privately derived classes that also have private access to protected members. When preceding the name of a base class, the protected keyword specifies that the public and protected members of the base class are protected members of its derived classes. Protected members are not as private as private members, which are accessible only to members of the class in which they are declared, but they are not as public as public members, which are accessible in any function. Protected members that are also declared as static are accessible to any friend or member function of a derived class. Protected members that are not declared as static are accessible to friends and member functions in a derived class only through a pointer to, reference to, or object of the derived class.

保护(c++)

私有成员只能在声明它的类中访问，而受保护成员可以在声明它的类中与它继承的类一起访问。