At the moment I have the following code:
typedef struct _hexagon {
int *vertice[6];
int *path[6];
int resourceType;
} hexagon;
typedef struct _game {
hexagon hexagons[5][5];
} Game;
and in the main I have:
Game g;
// This is the line that fails
g.hexagons[0][0].vertice[0] = 0;
This compiles fine but gives a segmentation fault. I have tried many variations, such as
g.hexagons[0][0].*vertice[0] = 0;
which doesn't compile. How do I access a pointer's memory from within a struct?
As vertice
is a array-of-pointes-to-integers
, to access vertice[0]
, you need to do *g.hexagons[0][0].vertice[0]
Sample program:
#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;
}
Output:
$ gcc -Wall -ggdb test.c
$ ./a.out
1
2
3
4
5
6
$
Hope it helps!
UPDATE: as pointed out by Luchian Grigore
The reason for the segmentation fault is explained by the following small program. In short, you are de-referencing a NULL pointer.
#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;
}
Now you can co-relate int *ip[]
with your g.hexagons[0][0].vertice[0]
I think you may have misunderstood what you have declared in _hexagon
. *vertice[6]
and your other array members are all arrays of pointers , so you have to treat each element like a pointer.
int x = 10;
g.hexagons[0][0].vertice[0] = &x;
Store the address of x
into pointer at position 0 of your array of pointers.
you might want to change following
int *vertice[6];
int *path[6];
to
int vertice[6];
int path[6];
Then it should work.
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