[Lang] 类成员修饰符

1. 访问

• public成员可以被任何代码访问，包括类的外部和派生类。
• protected 成员不能被类的外部直接访问，但可以被该类的派生类访问。
• private 成员只能在类内部访问，不能被类的外部或派生类直接访问。

2. 继承

• public 继承：基类public，protected，private在派生类中分别变成：public, protected, private
• protected 继承：基类public，protected，private在派生类中分别变成：protected, protected, private
• private 继承：基类public，protected，private在派生类中分别变成：private, private, private

3. 示例

public继承:

#include<iostream>
using namespace std;

class ParentClass
{
public:
    int x;
protected:
    int y;
private:
    int z;
};

class ChildClass : public ParentClass // x-public, y-protected, z-private
{
public:
    void fun()
    {
        cout << "x = " << x << endl;  
        cout << "y = " << y << endl; 
        // cout << "z = " << z << endl; // error: 'z' is a private member of 'ParentClass'
    }
};

class GrandChildClass : public ChildClass // x-public, y-protected, z-private
{
public:
    void fun()
    {
        cout << "x = " << x << endl; 
        cout << "y = " << y << endl;
        // cout << "z = " << z << endl; // error: 'z' is a private member of 'ChildClass'
    }
};

int main()
{
    ChildClass obj;
    obj.x = 10;
    // obj.y = 20; // error: 'y' is a protected member of 'ChildClass'
    // obj.z = 30; // error: 'z' is a private member of 'ChildClass'
    return 0;
}

protected继承:

#include<iostream>
using namespace std;

class ParentClass
{
public:
    int x;
protected:
    int y;
private:
    int z;
};

class ChildClass : protected ParentClass // x-protected, y-protected, z-private
{
public:
    void fun()
    {
        cout << "x = " << x << endl;  
        cout << "y = " << y << endl; 
        // cout << "z = " << z << endl; // error: 'z' is a private member of 'ParentClass'
    }
};

class GrandChildClass : protected ChildClass // x-protected, y-protected, z-private
{
public:
    void fun()
    {
        cout << "x = " << x << endl; 
        cout << "y = " << y << endl;
        // cout << "z = " << z << endl; // error: 'z' is a private member of 'ChildClass'
    }
};

int main()
{
    ChildClass obj;
    // obj.x = 10; // error: 'x' is a protected member of 'ChildClass'
    // obj.y = 20; // error: 'y' is a protected member of 'ChildClass'
    // obj.z = 30; // error: 'z' is a private member of 'ChildClass'
    return 0;
}

private继承:

#include<iostream>
using namespace std;

class ParentClass
{
public:
    int x;
protected:
    int y;
private:
    int z;
};

class ChildClass : private ParentClass // x-private, y-private, z-private
{
public:
    void fun()
    {
        cout << "x = " << x << endl;  
        cout << "y = " << y << endl; 
        // cout << "z = " << z << endl; // error: 'z' is a private member of 'ParentClass'
    }
};

class GrandChildClass : private ChildClass // x-private, y-private, z-private
{
public:
    void fun()
    {
        // cout << "x = " << x << endl; // error: 'x' is a private member of 'ChildClass'
        // cout << "y = " << y << endl; // error: 'y' is a protected member of 'ParentClass'
        // cout << "z = " << z << endl; // error: 'z' is a private member of 'ChildClass'
    }
};

int main()
{
    ChildClass obj;
    // obj.x = 10; // error: 'x' is a private member of 'ChildClass'
    // obj.y = 20; // error: 'y' is a private member of 'ChildClass'
    // obj.z = 30; // error: 'z' is a private member of 'ChildClass'
    return 0;
}