C++ - 找不到运算符

Question

我有一个填充了自定义类型值的向量，而 find() 算法抱怨它找不到合适的 == 运算符来进行值比较。我是这样实现的：

bool Ship::operator==(const Ship& source) {
    return (_type == source._type &&
            _damagedSquares == source._damagedSquares &&
            _orientation == source._orientation && _state == source._state);
}

我也尝试过“朋友”方法，但这也不起作用。 类本身的结构如下：

class Ship {
private:
    ShipType _type;
    int _damagedSquares;
    ShipOrientation _orientation;
    ShipState _state;

public:
    Ship();
    Ship(ShipType type);
    ~Ship();

    bool operator==(const Ship& source);
};

我在这里做错了什么？

附加信息：

std::vector<Ship> remainingShips;
MultiArray& squares = opponentGridCopy.GetSquares();
for (RowIterator rowIterator = squares.begin(); rowIterator != squares.end();
     ++rowIterator) {
    for (ColumnIterator columnIterator = rowIterator->begin();
         columnIterator != rowIterator->end(); ++columnIterator) {
        Square* current = &(*columnIterator);
        SquareState currentState = current->GetState();
        if (currentState != SquareState::Hit)
            current->SetState(SquareState::Vacant);
        Ship* potentialShip = current->GetOwner();
        if (potentialShip != nullptr) {
            int damagedSquares = potentialShip->GetDamagedSquares();
            if (!damagedSquares) {
                current->SetState(SquareState::Populated);
                break;
            }
            if (remainingShips.empty() ||
                std::find(remainingShips.begin(), remainingShips.end(),
                          potentialShip) ==
                    remainingShips.end()) // should be *potentialShip
                remainingShips.push_back(*potentialShip);
        }
    }
}
return remainingShips;

我正在传递一个指针作为比较值... 只需取消引用它，find() 现在就可以工作了。

Answer 1

像这样声明你的比较运算符：

bool Ship::operator==( const Ship &source ) const

注意结尾的const。

Answer 2

Ship* potentialShip = ...
std::find(remainingShips.begin(), remainingShips.end(), potentialShip)

你试图找到一个指针，而执行搜索的向量被定义为

std::vector<Ship> remainingShips;

您将指针与 Ship 对象进行比较，因此您的比较是错误的

bool Ship::operator==(const Ship& source) // Accepts a Ship reference, not a pointer

要修复它，要么取消引用指针，要么更改比较函数。

Answer 3

你的

bool operator==(const Ship& source);

也应该是const，即

bool operator==(const Ship& source) const;

但实际上，我更喜欢使用对称运算符，not 作为成员方法。 考虑：

Class Ship
{
private:
    ShipType _type;
    int _damagedSquares;
    ShipOrientation _orientation;
    ShipState _state;

public:
    Ship();
    Ship(ShipType type);
    ~Ship();

    static bool eq(const Ship& s0, const Ship& s1)
    {
        return (s0._type == s1._type &&
        s0.damagedSquares == s1._damagedSquares &&
        s0._orientation == s1._orientation &&
        s0._state == s1._state);
    }

};

inline bool operator==(const Ship& s0, const Ship& s1)
{
    return Ship::eq(s0, s1);
}