C++继承与访问权限解析-优快云博客

本文详细探讨了C++中的继承方式，包括public、protected和private继承，以及它们如何影响子类对父类成员的访问权限。通过实例代码展示了不同继承方式下，子类对象如何访问和使用父类的public、protected和private属性。强调了继承在对象和类角度上的访问规则，并提供了代码示例进行解释。

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#include<iostream>
using namespace std;
class father
{
private:
    int a;
protected:
    int b;
public:
    int c;
};

class son:public father
{
private:
    int a;
};

int main()
{
    cout<<sizeof(son)<<endl;
    return 0;
}

[root@Orz 10:36 ~]# run
16

结论：继承父类全部特性

公有继承：

子类继承方式	父类属性整合进子类
子类继承方式	public	protected	private
public继承	public	protected	禁止直接访问
protected继承	protected	protected	禁止直接访问
private继承	private	private	禁止直接访问

从对象角度：

一个对象只能访问一个类的共有属性，类的保护属性和私有属性是只有通过共有属性和友元函数间接访问

从类角度讲：

父类的保护属性，在子类中可以直接访问

父类的隐有属性，子类无法直接访问，这是一类区别另一个类的核心属性

1.公开继承public

#include<iostream>
using namespace std;
class Father
{
private:
    int a;
protected:
    int b;
public:
    int c;
    Father(int a = 1, int b = 2, int c = 3) :a(a), b(b), c(c) {}
    void print()
    {
        cout << "Father" << a << endl;
        cout << "Father" << b << endl;
        cout << "Father" << c << endl;
    }
};

class Son :public Father//公开继承
{
private:
    int d;
public:
    Son(int a = 1, int b = 2, int c = 3, int d = 4) :Father(a, b, c), d(d) {}
    void show()
    {
        //cout <<"Son from Father" << a << endl;//父类private无法直接访问
        cout << "Son from Father" << b << endl;//父类protected整合进子类protected
        cout << "Son from Father" << c << endl;//父类public整合进子类public
        cout << "Son" << d << endl;
    }
};

int main()
{
    Son son;
    son.c = 3;//继承Father public对外公开
    son.print();///继承Father protect对外公开
    son.show();
    return 0;
}

2.保护继承protected

#include<iostream>
using namespace std;
class Father
{
private:
    int a;
protected:
    int b;
public:
    int c;
    Father(int a = 1, int b = 2, int c = 3) :a(a), b(b), c(c) {}
    void print()
    {
        cout << "Father" << a << endl;
        cout << "Father" << b << endl;
        cout << "Father" << c << endl;
    }
};

class Son :protected Father//保护继承
{
private:
    int d;
public:
    Son(int a = 1, int b = 2, int c = 3, int d = 4) :Father(a, b, c), d(d) {}
    void show()
    {
        //cout <<"Son from Father" << a << endl;//父类private无法直接访问
        cout << "Son from Father" << b << endl;//父类protected仍然为子类protected
        cout << "Son from Father" << c << endl;//父类public沦为子类protected
        cout << "Son" << d << endl;
    }
};

int main()
{
    Son son;
    //son.c = 3;//父类public沦为子类protected,外界无法访问
    //son.print();//父类public沦为子类protected,外界无法访问
    son.show();
    return 0;
}

3.私有继承private

#include<iostream>
using namespace std;
class Father
{
private:
    int a;
protected:
    int b;
public:
    int c;
    Father(int a = 1, int b = 2, int c = 3) :a(a), b(b), c(c) {}
    void print()
    {
        cout << "Father" << a << endl;
        cout << "Father" << b << endl;
        cout << "Father" << c << endl;
    }
};

class Son :private Father//私有继承
{
private:
    int d;
public:
    Son(int a = 1, int b = 2, int c = 3, int d = 4) :Father(a, b, c), d(d) {}
    void show()
    {
        //cout <<"Son from Father" << a << endl;//父类private无访问
        cout << "Son from Father" << b << endl;//父类protected沦为子类private
        cout << "Son from Father" << c << endl;//父类public沦为子类private
        cout << "Son" << d << endl;
    }
};

int main()
{
    Son son;
    //son.c = 3;//父类public沦为子类protected,外界无法访问
    //son.print();//父类public沦为子类protected,外界无法访问
    son.show();
    return 0;
}