Question

:)我目前正在编写类的练习练习，在测试代码时遇到了一个问题：输入似乎没有正常工作，因为无论我输入什么向量，输出总是返回（有符号，如果我乘以负数）零向量。任何帮助将非常感谢！谢谢:)（也许我很迟钝，但我没看到问题在哪里

#include <cassert>
#include <iostream>
#include <sstream>
#include <string>

using namespace std;

class Vector {
private:
    double x, y, z; // Coordinates
    double scalar;

public:
    Vector(double x1, double y1, double z1) {
        x=x1; y=y1; z=z1;
    }

    Vector operator+ (Vector a) {
        x += a.x;
        y += a.y;
        z += a.z;
        return *this;
    }

    friend Vector operator* (Vector a, double scalar) {
        a.x *= scalar;
        a.y *= scalar;
        a.z *= scalar;
        return a;
    }

    friend Vector operator* (double scalar, Vector a) {
        a.x *= scalar;
        a.y *= scalar;
        a.z *= scalar;
        return a;
    }

    friend std::ostream& operator<< (std::ostream& o, Vector a) {
        o << "(" << a.x << ", " << a.y << ", " << a.z << ")";
        return o;
    }

    friend std::istream& operator>> (std::istream& i, Vector a) {
        char c;
        i >> c >> a.x >> c >> a.y >> c >> a.z >> c;
        return i;
    }

    double get(char i) const {
        if (i=='x') return x;
        if (i=='y') return y;
        if (i=='z') return z;
    }

};

Answer 1

我认为你operator>>中的问题。您应该像Vector那样传递friend std::istream& operator>> (std::istream& i, Vector& a) // ^的引用：

否则operator+是一个局部变量，它不会改变。

顺便说一下。您的+=作为Vector。它应该创建新的{{1}}。

Answer 2

我重构了你的程序以满足你的需要。尽管如此，还有很多优化的空间。

#include <iostream>
#include <sstream>
#include <string>

class Vector
{
private:
    double x, y, z; // Coordinates

public:
    Vector() : x(0), y(0), z(0) {}
    Vector(double x1, double y1, double z1) : x(x1), y(y1), z(z1) {}

    Vector operator+ (Vector const & rhs) const {
        return Vector(this->x + rhs.x, this->y + rhs.y, this->z + rhs.z);
    }

    friend Vector operator* (Vector const & lhs, double s) {
        return Vector(lhs.x * s, lhs.y * s, lhs.z * s);
    }

    friend Vector operator* (double s, Vector const & rhs) {
        return Vector(rhs.x * s, rhs.y * s, rhs.z * s);
    }

    friend std::ostream& operator<< (std::ostream & os, Vector const & a) {
        os << "(" << a.x << ", " << a.y << ", " << a.z << ")";
        return os;
    }

    friend std::istream& operator>> (std::istream & is, Vector & a) { // This needs to be a &, to be modified
        char c; // To dump extra characters
        is >> c >> a.x >> c >> a.y >> c >> a.z >> c;
        return is;
    }
    double get(char i) const {
        switch (i)
        {
            case 'x' : return x;
            case 'y' : return y;
            case 'z' : return z;
            default  : throw std::runtime_error("Vector doesn't contain specified character");
        }
    }
};

int main()
{
    Vector v1 = Vector(2.3, 3.5, 4.7); std::cout << v1 << std::endl;
    Vector v2 = Vector(1.4, 6.7, 1.1); std::cout << v2 << std::endl;
    Vector v3 = v1 + v2;               std::cout << v3 << std::endl;
    Vector v4 = 3 * v1;                std::cout << v4 << std::endl;
    Vector v5 = v2 * 5;                std::cout << v5 << std::endl;

    std::cout << v5.get('x') << std::endl;
    std::stringstream ss; ss << "(1,2,3)";
    Vector v6;                         std::cout << v6 << std::endl;
    ss >> v6;                          std::cout << v6 << std::endl;
    Vector v7 = 3 * v6;                std::cout << v7 << std::endl;
}

输出 -

$ g++  vector.cpp -o vector && ./vector
(2.3, 3.5, 4.7)
(1.4, 6.7, 1.1)
(3.7, 10.2, 5.8)
(6.9, 10.5, 14.1)
(7, 33.5, 5.5)
7
(0, 0, 0)
(1, 2, 3)
(3, 6, 9)

嗯，请仔细检查。如果您需要更多解释，我很乐意提供帮助。

自己的矢量类输入问题

2 个答案: