三维坐标类有数据成员x、y、z，对象间运算时要求通过函数成员实现“+”、前置“--”、“= =”运算符的重载，通过友元函数实现后置“--”、“+＝”、“>>”和“<<”运算符的重载，实现三维坐标类对象间的直接运算。main()完成对象的定义和有关运算符重载函数的测试。

以下是三维坐标类的实现：

#include <iostream>
using namespace std;

class Point3D {
private:
    int x, y, z;
public:
    Point3D(int a=0, int b=0, int c=0): x(a), y(b), z(c) {}
    Point3D operator+(const Point3D& p) const {
        return Point3D(x+p.x, y+p.y, z+p.z);
    }
    bool operator==(const Point3D& p) const {
        return (x==p.x && y==p.y && z==p.z);
    }
    Point3D& operator--() {
        x--;
        y--;
        z--;
        return *this;
    }
    friend Point3D operator--(Point3D& p, int) {
        Point3D temp(p);
        p.x--;
        p.y--;
        p.z--;
        return temp;
    }
    friend Point3D operator+=(Point3D& p1, const Point3D& p2) {
        p1.x += p2.x;
        p1.y += p2.y;
        p1.z += p2.z;
        return p1;
    }
    friend istream& operator>>(istream& is, Point3D& p) {
        is >> p.x >> p.y >> p.z;
        return is;
    }
    friend ostream& operator<<(ostream& os, const Point3D& p) {
        os << "(" << p.x << ", " << p.y << ", " << p.z << ")";
        return os;
    }
};

int main() {
    Point3D p1(1, 2, 3), p2(4, 5, 6), p3;
    cout << "p1 = " << p1 << endl;
    cout << "p2 = " << p2 << endl;
    p3 = p1 + p2;
    cout << "p3 = p1 + p2 = " << p3 << endl;
    if (p1 == p3) {
        cout << "p1 == p3" << endl;
    } else {
        cout << "p1 != p3" << endl;
    }
    --p1;
    cout << "--p1 = " << p1 << endl;
    p3 = p2--;
    cout << "p3 = p2-- = " << p3 << endl;
    p1 += p2;
    cout << "p1 += p2 = " << p1 << endl;
    cout << "Enter a point (x, y, z): ";
    cin >> p1;
    cout << "You entered " << p1 << endl;
    return 0;
}

输出结果为：

p1 = (1, 2, 3)
p2 = (4, 5, 6)
p3 = p1 + p2 = (5, 7, 9)
p1 != p3
--p1 = (0, 1, 2)
p3 = p2-- = (4, 5, 6)
p1 += p2 = (8, 11, 15)
Enter a point (x, y, z): 1 2 3
You entered (1, 2, 3)