用c++，建立一个点类，派生出圆类，再派生出圆柱体类，实现输入输出类对象

好的，下面是C++代码实现：

#include <iostream>
#include <cmath>
using namespace std;

// 点类
class Point {
public:
    Point(double x = 0, double y = 0, double z = 0): x(x), y(y), z(z) {}
    friend istream& operator>> (istream& in, Point& p) {
        in >> p.x >> p.y >> p.z;
        return in;
    }
    friend ostream& operator<< (ostream& out, const Point& p) {
        out << "(" << p.x << ", " << p.y << ", " << p.z << ")";
        return out;
    }
protected:
    double x, y, z;
};

// 圆类
class Circle : public Point {
public:
    Circle(double x = 0, double y = 0, double z = 0, double r = 0): Point(x, y, z), r(r) {}
    friend istream& operator>> (istream& in, Circle& c) {
        in >> static_cast<Point&>(c) >> c.r;
        return in;
    }
    friend ostream& operator<< (ostream& out, const Circle& c) {
        out << "Center: " << static_cast<const Point&>(c) << ", Radius: " << c.r;
        return out;
    }
protected:
    double r;
};

// 圆柱体类
class Cylinder : public Circle {
public:
    Cylinder(double x = 0, double y = 0, double z = 0, double r = 0, double h = 0): Circle(x, y, z, r), h(h) {}
    friend istream& operator>> (istream& in, Cylinder& cy) {
        in >> static_cast<Circle&>(cy) >> cy.h;
        return in;
    }
    friend ostream& operator<< (ostream& out, const Cylinder& cy) {
        out << "Base: " << static_cast<const Circle&>(cy) << ", Height: " << cy.h;
        return out;
    }
    double volume() const {
        return M_PI * r * r * h;
    }
protected:
    double h;
};

int main() {
    Point p;
    Circle c;
    Cylinder cy;

    cout << "Please input a point: ";
    cin >> p;
    cout << "The point you input is: " << p << endl;

    cout << "Please input a circle: ";
    cin >> c;
    cout << "The circle you input is: " << c << endl;

    cout << "Please input a cylinder: ";
    cin >> cy;
    cout << "The cylinder you input is: " << cy << endl;
    cout << "The volume of the cylinder is: " << cy.volume() << endl;

    return 0;
}

运行结果示例：

Please input a point: 1 2 3
The point you input is: (1, 2, 3)
Please input a circle: 1 2 3 4
The circle you input is: Center: (1, 2, 3), Radius: 4
Please input a cylinder: 1 2 3 4 5
The cylinder you input is: Base: Center: (1, 2, 3), Radius: 4, Height: 5
The volume of the cylinder is: 251.327