c - 访问结构数组时发生内存冲突

Question

我正处于指针学习曲线上，确实需要一些指导/帮助。我想要一个结构数组，每个结构都是一个跟踪各种事物的“单元”。一切似乎都工作正常，没有编译错误或任何东西，我正在使用数组来生成 map 。当我尝试在不同的点访问数组时，问题就出现了。有时我会遇到内存访问冲突，有时我不会 - 这意味着我很幸运。我对 C 非常陌生，因此我们将不胜感激，或者指出正确的方向。我真的很想了解为什么以及哪里出错了，我感觉这是我的指针和内存 - 我传递的东西是否正确？提前致谢。

#define ysize 20
#define xsize 80

typedef struct cells {
    int type;
    bool visited;
    bool passable;
    int item;
} cells;

int getCell(int x, int y, struct cells **map)
{
    return map[x + xsize * y]->type;
}
void setCell(int x, int y, int celltype, struct cells **map)
{
    map[x + xsize * y]->type = celltype;
}
struct cells **makeMap()
{
    struct cells **map = malloc(xsize * ysize * sizeof(struct cells *));
    for (int i = 0; i != xsize * ysize; i++) {
        map[i] = malloc(sizeof(struct cells ));
        map[i]->type = 0;
        map[i]->item = 0;
        map[i]->passable = true;
        map[i]->visited = false;
    }
    return map;
}


void main()
{
    struct cells ** map = makeMap();
    //getRand generates a random number between the min and max supplied.
    int x = getRand(0, xsize);
    int y = getRand(0, ysize);

    if (getCell(x, y, map) == tileCorridor || getCell(x, y, map) == tileDirtFloor){
        //map[x + xsize * y]->item = 3;
        //printf("%d", getCell(x, y, map));
    }
    // this is where the code is failing. 
    //sometimes it works, others it generates a memory error

    destroyMap(map);
}

Answer 1

由于您正在对一维进行索引计算，因此不需要二维数组。这是您的代码的功能版本。我临时改进了 getRand 并删除了 destroyMap ，这两者仍然缺失，并添加了包含内容。

由于发布的代码主要有效，因此错误可能在其他地方。可能您的索引超出范围。

#include <malloc.h>
#include <stdlib.h>

#define ysize 20
#define xsize 80

typedef struct cells {
    int type;
    bool visited;
    bool passable;
    int item;
} cells;

int getCell(int x, int y, struct cells *map)
{
    return map[x + xsize * y].type;
}
void setCell(int x, int y, int celltype, struct cells*map)
{
    map[x + xsize * y].type = celltype;
}
struct cells *makeMap()
{
    struct cells *map = (cells*) malloc(xsize * ysize * sizeof(struct cells));
    for (int i = 0; i != xsize * ysize; i++) {
        map[i].type = i;
        map[i].item = 0;
        map[i].passable = true;
        map[i].visited = false;
    }
    return map;
}


int main()
{
    struct cells * map = makeMap();
    //getRand generates a random number between the min and max supplied.

    for( int i = 0; i < 10000; ++i)
    {
        int x = rand() % xsize;
        int y = rand() % ysize;

        int tileCorridor = 21;
        int tileDirtFloor = 143;


        if (getCell(x, y, map) == tileCorridor || getCell(x, y, map) == tileDirtFloor){
            //map[x + xsize * y]->item = 3;
            printf("%d at [%d, %d] \n", getCell(x, y, map), x , y);
        }
        // this is where the code is failing. 
        //sometimes it works, others it generates a memory error
    }
    free(map);
}

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