Copying multi char array to another multi char array

Question

I'm converting Java code to C, and something as simple as swapping contents of multi arrays in Java:

boolean[][] temp = board;
board = nextBoard;
nextBoard = temp;

Seems to be a lot more troublesome in C.

After viewing similar questions on this site, I have learned that I have to use memcpy which I initiated in a method called arrayCopy.

This is arrayCopy:

 void arrayCopy(char * a, char * b)
 {
     struct universe data;
     int r;
     for(r = 0; r < data.rows; r++)
     memcpy(b, a, sizeof(a));
 }

Which I call from the main method:

char temp[SIZE][SIZE];
arrayCopy(&data.board, &temp);
arrayCopy(&data.nextBoard, &data.board);
arrayCopy(&temp, &data.nextBoard);

With the following struct:

struct universe
{
  char board[SIZE][SIZE];
  char nextBoard[SIZE][SIZE];
  int columns;
  int rows;
}universe;

But I'm getting warnings such as:

A2Q1.c:189:15: warning: incompatible pointer types passing 'char (*)[60][60]' to parameter of type 'char *'

Yet memcpy only returns pointers, so I can't switch the parameters. I also can't use malloc() yet as other questions suggest because I have not learned it yet, so any other suggestions would be appreciated.

Answer 1

try this

void swapBoard(struct universe *x){
    char temp[SIZE][SIZE];
    memcpy(temp, x->board, sizeof(temp));
    memcpy(x->board, x->nextBoard, sizeof(temp));
    memcpy(x->nextBoard, temp, sizeof(temp));
}
int main(){
    struct universe data;
    //...
    swapBoard(&data);

Answer 2

I think you are making it a bit over-complicated. You can use memcpy directly in your example above to copy everything from a to b without iterating through it. If you run this code...

int main()
{
    char temp[60][60];
    printf("%d", sizeof(temp));
}

You'll see that sizeof will give you 3600 bytes, 60*60 to the total bytes allocated by the array. These byte are allocated in a contiguous chunk of memory and memcpy can copy them in one swoop. This demonstrates the point:

int main()
{
    char temp[60][60];
    memset(temp, 'a', sizeof(temp));
    char temp2[60][60];
    memset(temp2, 'b', sizeof(temp2));
    memcpy(temp2, temp, sizeof(temp2));
    printf("%c", temp2[23][34]);
}

The printf will print 'a'. In your code above, this should work just fine:

char temp[SIZE][SIZE];
memcpy(data.board, temp, sizeof(data.board));
memcpy(data.nextBoard, data.board, sizeof(data.nextBoard));
memcpy(temp, data.nextBoard, sizeof(temp));

Note that this assumes all of these arrays are identical in size. You may want to create a minsize function or use a macro function like #define MINSIZE(a,b) (sizeof((a)) < sizeof((b)) ? sizeof((a)) : sizeof((b))) to be safe.