要调用的 C++ 不匹配函数

Question

我可以知道这些代码有什么问题吗？

#include <iostream>

using namespace std;

class Vehicle
{
    double price = 0;
public:
    void setPrice(double p)
    {
        price = p;
    }
    double comparePrices(const Vehicle&, Vehicle&);
};

double Vehicle::comparePrices(const Vehicle& car1, Vehicle& car2)
{
    cout << "Enter the price for the used car: ";
    double price;
    cin >> price;
    car2.setPrice(price);
    return car1.price - car2.price;
}

int main()
{
    Vehicle newCar, usedCar;
    double diff;
    newCar.setPrice(38000);
    diff = newCar.comparePrices(newCar, usedCar);
    cout << "Used car price is $" << usedCar.setPrice();
    cout << ", the difference is $" << diff << endl;
}

执行后报错

error: no matching function for call to 'Vehicle::setPrice()'|

Answer 1

我看到了一些错误:

using namespace std;

改掉使用它的习惯。参见 Why is "using namespace std" considered bad practice? .

double comparePrices(const Vehicle&, Vehicle&);

comparePrices()是非 static方法，这意味着您需要在 Vehicle 上调用它对象，以及传入两个 Vehicle对象作为输入参数。这有点浪费和多余。要么制作comparePrices()静态，否则删除其中一个 Vehicle参数并使用隐式 this访问被调用对象的参数。

此外，仅从设计角度来看，comparePrices()不应提示用户输入。该工作属于 main()打电话前comparePrices() .

cout << "Used car price is $" << usedCar.setPrice();

setPrice()需要 double作为输入，但您没有传入 double值(value)。这就是编译器错误所提示的。

此外，setPrice()没有返回值，它的返回类型是void , 所以你不能把它传递给 operator<< .您需要添加一个单独的 getPrice() Vehicle 的方法类返回其 price成员(member)。

话虽如此，试试这个:

#include <iostream>

class Vehicle
{
private:
    double price = 0;
public:
    double getPrice() const
    {
        return price;
    }

    void setPrice(double p)
    {
        price = p;
    }

    static double comparePrices(const Vehicle&, const Vehicle&);
};

double Vehicle::comparePrices(const Vehicle& v1, const Vehicle& v2)
{
    return v1.price - v2.price;
}

int main()
{
    Vehicle newCar, usedCar;
    double price, diff;

    newCar.setPrice(38000);

    std::cout << "Enter the price for the used car: ";
    std::cin >> price;
    usedCar.setPrice(price);

    diff = Vehicle::comparePrices(newCar, usedCar);
    std::cout << "Used car price is $" << usedCar.getPrice();
    std::cout << ", the difference is $" << diff << std::endl;

    return 0;
}

或者这个:

#include <iostream>

class Vehicle
{
private:
    double price = 0;
public:
    double getPrice() const
    {
        return price;
    }

    void setPrice(double p)
    {
        price = p;
    }

    double comparePrices(const Vehicle&);
};

double Vehicle::comparePrices(const Vehicle& other)
{
    return price - other.price;
}

int main()
{
    Vehicle newCar, usedCar;
    double price, diff;

    newCar.setPrice(38000);

    std::cout << "Enter the price for the used car: ";
    std::cin >> price;
    usedCar.setPrice(price);

    diff = newCar.comparePrices(usedCar);
    std::cout << "Used car price is $" << usedCar.getPrice();
    std::cout << ", the difference is $" << diff << std::endl;

    return 0;
}