c++ - error LNK2019 未解析的外部函数

Question

当我编译我的程序时，我得到:

程序工作，如果我评论这些部分(功能车辆::驱动器):

if (check_position(pos, number, 1, 0))
    continue;
change_position(pos, number, 1, 0);

函数 change_position & check_position (terrain.cpp):

void change_position(vehicles::position &pos, int number, int vertical, int horizontal){
        pos.x[number] = pos.x[number] + vertical;
        pos.y[number] = pos.y[number] + horizontal;
}

bool check_position(vehicles::position &pos, int number, int vertical, int horizontal)
{
    if (pos.x[number] + vertical > MAX_SIZE || pos.x[number] + vertical < 0)
        return true;
    if (pos.y[number] + horizontal > MAX_SIZE || pos.y[number] + horizontal < 0)
        return true;
    return false;
}

Function vehicles::drive (mechanics.cpp)，未完成但在上面的代码注释后工作:

void vehicles::drive(int move, vehicles::position &pos, int number)
{
    int direction;
    cout << "Press W,A,S,D to move or Q to quit\n\n";

    while (move)
    {
        if (move <= 0)
            break;
        cin >> direction;
        switch (direction)
        {
        case 'w':
        case 'W':
            if (check_position(pos, number, 1, 0))
                continue;
            change_position(pos, number, 1, 0);
            --move;
            break;
        case 'q':
        case 'Q':
            break; 
        default:
            cout << "Press W,A,S,D to move or Q to quit\n\n";
            break;
        }
    }

类车辆(vehickles.h):

class vehicles{
protected:
    double durability;
    double velocity;
public:
     vehicles(double d, double v) : durability(d), velocity(v) {}
     ~vehicles() {}

     struct position{
         vector<int> x;
         vector<int> y;
     }pos;

     void drive(int move, position &pos, int number);
     void info() { cout << durability << " " << velocity << "\n"; }
};

这些函数的声明:

void change_position(vehicles::position, int, int, int);
bool check_position(vehicles::position, int, int, int);

Answer 1

问题是您的声明与定义不匹配。声明通过值获取第一个参数，而定义通过引用获取它。在 C++ 中，这些必须完全匹配，否则链接器在使用函数重载时将不知道使用哪一个。您可以通过将声明更新为以下内容来轻松解决此问题

void change_position(vehicles::position&, int, int, int);
//                                     ^
bool check_position(vehicles::position&, int, int, int);
//                                    ^

我建议您更改 check_position 函数以通过 const 引用获取第一个参数，因为该函数不会修改它。

bool check_position(const vehicles::position&, int, int, int);