通过组合访问父类

Question

In my program i have a very simple structure to represent a map in an RPG game. I have a Map class, with a 2d Array, "Grid", made out of Area objects, like so:

 #pragma once
 #include "Area.h"

 class Map
 {
 public:
     Map();
     ~Map();

     Area Grid[10][10];
 };

Then in the Map constructor:

 Map::Map()
 {
for (int y = 0; y < 10; y++) {
    for (int x = 0; x < 10; x++) {
        Grid[x][y] = Area();
    }
}
}

I would like for the Area objects to be able to access certain values from the Map object, and I've read that i could include a reference to the map class when constructing the area object, so that it can refer back to its parent. But to do this, i would have to #include "Map.h" in Area.h, which would create an include loop, and just not be very good in general. So how would i go about injecting a reference to the area's parent in each area object? Thanks for any help in advance.

Answer 1

// Area.h
#pragma once
struct Map;

struct Area {
    Map* map = nullptr;
    Area() {}
    explicit Area( Map* m) : map(m) {}
};

Note that you may want to have some of the functions of Area defined in Area.cpp (that includes Map.h). I just left it out for simplicity of example code.

// Map.h
#pragma once
#include "Area.h"

struct Map
{
    Map();
    ~Map();

    Area Grid[10][10];
};

// Map.cpp
#include "Map.h"

Map::Map()
{
    for (int y = 0; y < 10; y++) {
        for (int x = 0; x < 10; x++) {
            Grid[x][y] = Area(this);
        }
    }
}

Map::~Map() {}

// main.cpp
#include "Map.h"
int main()
{
    Map m;
    return 0;
}