Question

我为我的一个班级制作了一个项目，我很确定我几乎完成了这个项目。基本上我必须输入2人的门票，我必须找到最高和最低价格。我需要重载*和/运算符来修复项目的问题。此外，通过教师的指示，friend声明是此项目的必要条件。

现在，对于这个问题。我试图将正确的票证变量（t1或t2）存储到t3中，这样我就可以将它返回到主变量。当我使用＆＃34; =＆＃34;要设置t1到t3，它说＆＃34;没有可行的超载＆＃39; =＆＃39;＆＃34;。以下是我的代码：

#include <iostream>

using namespace std;

class ticket
{
public:
    ticket();
    double input();
    double output();
    friend ticket operator *(const ticket &t1, const ticket &t2);
    friend ticket operator /(const ticket &t1, const ticket &t2);
private:
    void cost();
    string name;
    double miles, price;
    int transfers;
};


int main()
{
    ticket customer1, customer2, customer3;

    //------------------------------------------------
    cout << "*** Customer 1 ***" << endl;
    customer1.input();
    cout << "--- Entered, thank you ---" << endl;


    cout << "*** Customer 2 ***" << endl;
    customer2.input();
    cout << "--- Enter, thank you ---" << endl;
    //------------------------------------------------



    //------------------------------------------------
    cout << "Testing of the * operator: " << endl;
    customer3 = customer1 * customer2;
    cout << "*** Database printout: ***" << endl;
    customer3.output();
    cout << endl;
    cout << "--- End of Database ---" << endl;
    //------------------------------------------------


    //------------------------------------------------
    cout << "Testing of the / operator:" << endl;
    customer3 = customer1 / customer2;
    cout << "*** Database printout: ***" << endl;
    customer3.output();
    cout << endl;
    cout << "--- End of Database ---" << endl;
    //------------------------------------------------


        return 0;
}

ticket operator *(const ticket &t1, const ticket &t2)
{
    ticket t3;

    if (t1.price > t2.price)
        t3 = t1.price;
    else
        t3 = t2.price;
    return t3;
}
ticket operator /(const ticket &t1, const ticket &t2)
{
    ticket t3;

    if (t1.price < t2.price)
        t3 = t1.price;
    else
        t3 = t2.price;
        return t3;
}
ticket::ticket()
{
}

double ticket::input()
{
    cout << "Miles? ";
    cin >> miles;

    cout << endl << "Transers? ";
    cin >> transfers;

    cout << endl << "Name? ";
    cin >> name;

    cost();

    cout << endl << "Price is: " << price << endl;

    return miles;
}

double ticket::output()
{
    cout << name << '\t' << miles << "mi \t " << transfers << " transfers \t" << price;
    return miles;
}

void ticket::cost()
{
    price = (.5 * miles) - (50 * transfers);
}

Answer 1

您没有为operator=定义ticket，其中以double为参数。因此，您无法为ticket个对象分配双打。

Answer 2

这就是我得到相同编译错误的方法。我将我的一个getter函数标记为const，而我仍想修改类成员变量。请参阅以下简单示例：

class CPath {
private: 
    std::string m_extension; 
public: 
    std::string GetExtension() const {
        if (m_extension.length()==0) {
            m_extension = "txt";
        }
        return m_extension; 
    }
}

在这种情况下，我们有两个解决方案：

1）在函数定义中删除const修饰符;
2）将属性m_extension标记为mutable。

Answer 3

您可能希望拥有会员功能

set_price(const& double price)

所以你可以改变这样的错误代码，这样会更好

 if (t1.price > t2.price)
        t3.set_price(t1.price);
    else
        t3.set_price(t2.price);

“没有可行的超载'='”为什么？

3 个答案: