C++ Private和Protected的區別用法及代碼示例

// C++ program to demonstrate
// protected access modifier
#include <bits/stdc++.h>
using namespace std;
// base class
class Parent {
    // protected data members
protected:
    int id_protected;
};
// sub class or derived class
class Child : public Parent {
public:
    void setId(int id)
    {
        // Child class is able to access the inherited
        // protected data members of the base class
        id_protected = id;
    }
    void displayId()
    {
        cout << "id_protected is: "
             << id_protected << endl;
    }
};
// main function
int main()
{
    Child obj1;
    // member function of the derived class can
    // access the protected data members of the base class
    obj1.setId(81);
    obj1.displayId();
    return 0;
}

// C++ program to demonstrate private
// access modifier
#include <iostream>
using namespace std;
class Circle {
    // private data member
private:
    double radius;
    // public member function
public:
    void compute_area(double r)
    {
        // member function can access private
        // data member radius
        radius = r;
        double area = 3.14 * radius * radius;
        cout << "Radius is: " << radius << endl;
        cout << "Area is: " << area;
    }
};
// main function
int main()
{
    // creating object of the class
    Circle obj;
    // trying to access private data member
    // directly outside the class
    obj.compute_area(1.5);
    return 0;
}