C++ 类的继承 -- private

基类指针(or ref)可以指向 所有 的子类 (e.g., overriding)，除了private 子类的所有子类 。意味着 private class 可用于隔断上下层的类的访问。

e.g., void memfcn (Base &b) { b = *this;} in class drv_from_Drv3

class Base

{

public:

    double dBPublic = 0.1;

protected:

    double dBProtect = 0.2;

private:

    double dBPrivate = 0.3;

};

class Drv1 : public Base

{

public:

    double dpubdrvPublic = 1.1;

    void memfcn(Base &b) {b = *this;}

protected:

    double dpubdrvProtect = 1.2;

private:

    double dpubdrvPrivate = 1.3;

};

class Drv2 : protected Base

{

public:

    double dprodrvPublic = 2.1;

    void memfcn(Base &b) {b = *this;}

protected:

    double dprodrvProtect = 2.2;

private:

    double dprodrvPrivate = 2.3;

};

class Drv3 : private Base

{

public:

    double dpridrvPublic = 2.1;

    void memfcn(Base &b) {b = *this;}

protected:

    double dpridrvProtect = 2.2;

private:

    double dpridrvPrivate = 2.3;

};

class drv_from_Drv1 : public Drv1

{

public:

    double dpubdrvPublic = 3.1;

    void memfcn(Base &b) {b = *this;}

protected:

    double dpubdrvProtect = 3.2;

private:

    double dpubdrvPrivate = 3.3;

};

class drv_from_Drv2 : public Drv2

{

public:

    double dpubdrvPublic = 4.1;

    void memfcn(Base &b) {b = *this;}

protected:

    double dpubdrvProtect = 4.2;

private:

    double dpubdrvPrivate = 4.3;

};

class drv_from_Drv3 : public Drv3

{

public:

    double dpubdrvPublic = 5.1;

    void memfcn(Base &b) {b = *this;} //编译报错.

//原因: Drv3 is private, all the member that Drv3 inherit from Base are private.

protected:

    double dpubdrvProtect = 5.2;

private:

    double dpubdrvPrivate = 5.3;

};