c++ - 基本hunter/prey练习中的“Invalid use of incomplete type”

因此，我目前的任务是进行基本的Hunter and Prey模拟，在遇到其他一些问题之后，我的教授建议我将所有内容都放入main.cpp中，以使该功能暂时生效。

我当前的问题是，在Creature::Find()函数中，它声称Grid类是不完整的，即使它已在文件顶部预先声明。我最初的想法是将Grid类放在Creature之前，但这会导致更多或相同的错误(指的是Creature不完整)，因为Grid本质上是Creature指针的2D数组。以下是代码的相关位，可以在Dropbox here上找到整个文件。

class Grid;  //*** error: forward declaration of 'class Grid'

//Other stuff...

class Creature
{
public:
    Grid* theGrid;
    Coords position;
    int stepBreed;
    int stepHunger;
    char face;
    bool hasMoved;

    Creature(Grid* _grid, Coords _position, char _face)  //Constructor
    {
        theGrid = _grid;
        position = _position;
        face = _face;
        stepBreed = stepHunger = 0;
        hasMoved = false;
    }

    vector<Coords> Find(char thisFace)  //Returns a list of coords with prey on them
    {
        vector<Coords> result;
        for(int i = position.x-1; i <= position.x+1; i++)
            for(int j = position.y-1; j <= position.y+1; j++)
            {
                Coords temp(i,j);
                if(theGrid->Occupant(temp) == thisFace) //*** error: invalid use of incomplete type 'class Grid'
                    result.push_back(temp);
            }
        return result;
    }

    virtual Coords Move() = 0;  //Allows the creature type to define it's own movement
    virtual Coords Breed() = 0;  //Allows the creature type to define it's own breeding
    virtual bool Starve() = 0;  //Allows the creature type to starve of its own accord
};

class Grid
{
public:
    Creature* grid[MAX_X][MAX_Y];

    Grid() //Initalizes the grid and spawns random creatures
    {
        cout<<endl<<"grid init"<<endl;
        for(int i = 0; i < MAX_X; i++)
            for(int j = 0; j < MAX_Y; j++)
                grid[i][j] = NULL;
    }

    void Move() //Tells each creature on the grid to move
    {
        cout<<endl<<"---  Grid::Move() TOP  ---"<<endl<<endl;
        ResetMoved();

        for(int i = 0; i < MAX_X; i++)
            for(int j = 0; j < MAX_Y; j++)
                if(grid[i][j])
                    grid[i][j]->Move();
        cout<<endl<<"---  Grid::Move() BOTTOM  ---"<<endl<<endl;
    }

    void Breed() //Tells each creature to breed (if it can)
    {

    }

    void Kill()  //Tells each creature to die (if it's old)
    {

    }

    char** Snapshot()  //Creates a char array "snapshot" of the board
    {
        char** result = new char*[MAX_X];
        for(int i = 0; i < MAX_X; i++)
        {
            result[i] = new char[MAX_Y];
            for(int j = 0; j < MAX_Y; j++)
            {
                result[i][j] = Occupant(Coords(i, j));
            }
        }
        return result;
    }

    Creature* Get(Coords here)  //Returns a pointer to the object at the specified position
    {
        return grid[here.x][here.y];
    }

    char Occupant(Coords here) //Returns the character of the specified position
    {
        if(!Get(here))
            return FACE_EMPTY;
        return Get(here)->face;
    }

    void Clear(Coords here)  //Deletes the object at the specified position
    {
        cout<<endl<<"---  Grid::Clear() TOP  ---"<<endl<<endl;

        if(!Get(here))
        {
            cout<<"   inside if"<<endl;
            delete Get(here);
        }
        cout<<"   outside if"<<endl;
        grid[here.x][here.y] = NULL;

        cout<<endl<<"---  Grid::Clear() BOTTOM  ---"<<endl<<endl;
    }

    void ResetMoved()
    {
        for(int i = 0; i < MAX_X; i++)
            for(int j = 0; j < MAX_Y; j++)
                if(grid[i][j])
                    grid[i][j]->hasMoved = false;
    }
};

编辑:预览和标记工具栏由于某些原因无法正常工作。

最佳答案

您有一个循环依赖性(我似乎记得您之前有这个问题)。将内容放在同一文件中并不能真正解决问题(尽管也许可以帮助您更清楚地看到问题)。您要做的是正确地排序事物，以便在每个函数需要的类之后定义它们。

在这种情况下，我会这样

class Grid;

class Creature
{
public:
    Grid* theGrid;
    ...
    vector<Coords> Find(char thisFace);
    ...
};

class Grid
{
public:
    Creature* grid[MAX_X][MAX_Y];
    ...
};

vector<Coords> Creature::Find(char thisFace)
{
   ...
}

Creature::Find同时需要Creature类和Grid类，因此必须在两个类都已完全定义之后使用。

如果最终将Creature::Find定义放在头文件中，则必须添加inline关键字，否则将获得多个定义。

关于c++ - 基本hunter/prey练习中的“Invalid use of incomplete type”，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/16117546/