c - 访问结构中的指针

Question

目前我有以下代码:

typedef struct _hexagon {
    int *vertice[6];
    int *path[6];
    int resourceType;
} hexagon;


typedef struct _game {
    hexagon hexagons[5][5];
} Game;

主要是我有:

Game g;
// This is the line that fails
g.hexagons[0][0].vertice[0] = 0;

这可以正常编译，但会出现段错误。我尝试了很多变体，例如

g.hexagons[0][0].*vertice[0] = 0;

无法编译。如何从结构中访问指针的内存？

Answer 1

因为vertices是一个array-of-pointes-to-integers，要访问vertice[0]，你需要做*g.hexagons[0][0].顶点[0]

示例程序:

#include <stdio.h>

typedef struct _hexagon {
    int *vertice[6];
    int *path[6];
    int resourceType;
} hexagon;


typedef struct _game {
    hexagon hexagons[5][5];
} Game;

int main()
{
    int i1 = 1;
    int i2 = 2;
    int i3 = 3;
    int i4 = 4;
    int i5 = 5;
    int i6 = 6;

    Game g;
    g.hexagons[0][0].vertice[0] = &i1;
    g.hexagons[0][0].vertice[1] = &i2;
    g.hexagons[0][0].vertice[2] = &i3;
    g.hexagons[0][0].vertice[3] = &i4;
    g.hexagons[0][0].vertice[4] = &i5;
    g.hexagons[0][0].vertice[5] = &i6;

    printf("%d \n", *g.hexagons[0][0].vertice[0]);
    printf("%d \n", *g.hexagons[0][0].vertice[1]);
    printf("%d \n", *g.hexagons[0][0].vertice[2]);
    printf("%d \n", *g.hexagons[0][0].vertice[3]);
    printf("%d \n", *g.hexagons[0][0].vertice[4]);
    printf("%d \n", *g.hexagons[0][0].vertice[5]);

    return 0;   
}

输出:

$ gcc -Wall -ggdb test.c 
$ ./a.out 
1 
2 
3 
4 
5 
6 
$ 

希望对您有所帮助!

---

更新:正如 Luchian Grigore 所指出的

segmentation fault的原因由下面的小程序解释。简而言之，您正在取消引用 NULL 指针。

#include <stdio.h>

/*
int *ip[3];
+----+----+----+
|    |    |    |
+----+----+----+
   |    |    |
   |    |    +----- points to an int *
   |    +---------- points to an int *
   +--------------- points to an int *

ip[0] = 0;
ip[1] = 0;
ip[2] = 0;

+----+----+----+
|    |    |    |
+----+----+----+
   |    |    |
   |    |    +----- NULL
   |    +---------- NULL
   +--------------- NULL

*ip[0] -> dereferencing a NULL pointer ---> segmantation fault
*/

int main()
{
    int * ip[3];
    ip[0] = 0;
    ip[1] = 0;
    ip[2] = 0;

    if (ip[0] == NULL) {
        printf("ip[0] is NULL \n");
    }

    printf("%d \n", *ip[0]);
    return 0;
}

现在您可以将 int *ip[] 与您的 g.hexagons[0][0].vertice[0]

关联起来