C++中protected，private，public三者的区别详解

#include <iostream>

class Base {
public:
    int pub = 1;          // 公开成员
protected:
    int prot = 2;         // 受保护成员
private:
    int priv = 3;         // 私有成员
};

class Derived : public Base {
public:
    void show() {
        std::cout << pub << "\n";   // ✅ 可访问
        std::cout << prot << "\n";  // ✅ 可访问（protected对子类可见）
        // std::cout << priv << "\n";  // ❌ 不可访问（private对子类隐藏）
    }
};

int main() {
    Base b;
    Derived d;

    std::cout << b.pub << "\n";     // ✅ public 对外可访问
    // std::cout << b.prot << "\n";  // ❌ protected 不可外部访问
    // std::cout << b.priv << "\n";  // ❌ private 不可外部访问
}

class Base {
public:
    int a;
protected:
    int b;
private:
    int c;
};

class Derived1 : public Base {};
class Derived2 : protected Base {};
class Derived3 : private Base {};

class Animal {
public:
    void eat() { std::cout << "eat\n"; } // 公共接口
protected:
    void breathe() { std::cout << "breathe\n"; } // 子类能用
private:
    void think() { std::cout << "think\n"; } // 仅自己能用
};

class Dog : public Animal {
public:
    void run() {
        eat();      // ✅ 继承自public
        breathe();  // ✅ 继承自protected
        // think(); // ❌ 无法访问
    }
};

class Widget {
public:
    void draw();         // 对外接口
protected:
    virtual void paint(); // 由子类重写的绘制逻辑
};