c/c++再学习：C++中public、protect、private的访问权限控制

#include <iostream>

class ReferencePerission
{
    friend class FriendClass;
    friend void FriendFunc();
public:
    int public_num;
    void public_func(){std::cout <<"public_func "<<public_num<<std::endl;}
protected:
    int protected_num;
    void protected_func(){std::cout <<"protected_func "<<protected_num<<std::endl;}
private:
    int private_num;
    void private_func(){std::cout <<"private_func "<<private_num<<std::endl;}
};

class FriendClass
{
public:
    FriendClass() {
        std::cout<<"FriendClass"<<std::endl;
        ReferencePerission ref;
        ref.public_num = 1;
        ref.protected_num = 2;
        ref.private_num = 3;
        ref.public_func();
        ref.protected_func();
        ref.private_func(); 
    }
    
    ~FriendClass()
    {
        
    }
};

void FriendFunc()
{
    std::cout<<"FriendFunc"<<std::endl;
    ReferencePerission ref;
    ref.public_num = 1;
    ref.protected_num = 2;
    ref.private_num = 3;
    ref.public_func();
    ref.protected_func();
    ref.private_func();     
}

int main()
{
    ReferencePerission ref;
    
    ref.public_num = 1;
    //ref.protected_num = 2;    /* 编译出错 declared protected here */
    //ref.private_num = 3;      /* 编译出错 declared private here */
    ref.public_func();
    //ref.protected_func();     /* 编译出错 declared protected here */
    //ref.private_func();       /* 编译出错 declared private here */    
    
    FriendFunc(); /* 友元函数可以访问public,protected,private成员变量和函数 */
    
    FriendClass friendObj; /* 友元类可以访问public,protected,private成员变量和函数 */
    
    return 0;
}

#include <iostream>

using namespace std;

class InheritPerission
{
public:
    string public_str;
    void public_func(){std::cout <<"public_func "<<public_str<<std::endl;}
protected:
    string protected_str;
    void protected_func(){std::cout <<"protected_func "<<protected_str<<std::endl;}
private:
    string private_str;
    void private_func(){std::cout <<"private_func "<<private_str<<std::endl;}
};

/*派生类通过public继承，基类的各种权限不变*/
class InheritPublic : public InheritPerission
{
public:
    InheritPublic(){
        /*派生类的成员函数，可以访问基类的public成员、protected成员，但是无法访问基类的private成员*/
        public_str = "public_str";
        protected_str = "protected_str";
        //private_str = "private_str";
        public_func();
        protected_func();
        //private_func(); 
    }
    ~InheritPublic(){};
};

/*派生类通过protected继承，基类的public成员在派生类中的权限变成了protected 。protected和private不变*/
class InheritProtected : protected InheritPerission
{
public:
    InheritProtected(){
        /*派生类的成员函数，可以访问基类的public成员、protected成员，但是无法访问基类的private成员*/
        public_str = "public_str";
        protected_str = "protected_str";
        //private_str = "private_str";
        public_func();
        protected_func();
        //private_func();
    }
    ~InheritProtected(){}
};

/*派生类通过private继承，基类的所有成员在派生类中的权限变成了private*/
class InheritPrivate : private InheritPerission
{
public:
    InheritPrivate(){
        /*派生类的成员函数，可以访问基类的public成员、protected成员，但是无法访问基类的private成员*/
        public_str = "public_str";
        protected_str = "protected_str";
        //private_str = "private_str";
        public_func();
        protected_func();
        //private_func();
    }
    ~InheritPrivate(){}
};


int main()
{
    InheritPublic inheritPublic;
    InheritProtected inheritProtected;
    InheritPrivate inheritPrivate;
    
    /*派生类的实例变量，可以访问基类的public成员，但是无法访问protected、private成员*/
    inheritPublic.public_func();
    //inheritPublic.protected_func();
    //inheritPublic.private_func();
    
    /*派生类的实例变量，无法访问基类的任何成员，因为基类的public成员在派生类中变成了protected*/
    //inheritProtected.public_func();
    //inheritProtected.protected_func();
    //inheritProtected.private_func();
    
    /*派生类的实例变量，无法访问基类的任何成员，因为基类的所有成员在派生类中变成了private*/
    //inheritPrivate.public_func();
    //inheritPrivate.protected_func();
    //inheritPrivate.private_func();
    
    return 0;
}