error: array type has incomplete element type typedef

Question

i'm making a game of life in C. I was told to use typedef and enum wherever possible, so I made a typedef state to signal whether a cell is DEAD or ALIVE. I made a 3d array that holds all the boards in all generations. when I try to use the array as a parameter of a function, it says error: array type has incomplete element type. Did I do the typedef wrong? Can you not have arrays of user defined types? Here's my code:

#include <stdio.h>
#include <stdlib.h>
typedef enum { DEAD, ALIVE } state;
void nextGeneration(state[][][], int, int, int);
int numberOfNeighbours(state[][][], int, int, int);
void printGeneration(state[][][], int, int, int);
int main(void)
{
        FILE *filePath;
        int boardHeight;
        int boardWidth;
        int requestedGenerations;
        state board[100][10][10] = { DEAD };
        int h;
        int w;
        if((filePath = fopen("file1", "r")) == NULL)
        {
                fprintf(stderr, "No such file.\n");
                exit(1);
        }
        if(fscanf(filePath, "%d %d %d", &requestedGenerations, &boardHeight, &boardWidth) != 3)
        {
                fprintf(stderr, "File doesn't contain the number of requested generations or the board's size.\n");
                exit(2);
        }
        for (h = 0; h < boardHeight; h++)
                for(w = 0; w < boardWidth; w++)
                        fscanf(filePath, "%d", &board[0][h][w]);
        while(requestedGenerations > 0)
        {
                nextGeneration(board, requestedGenerations--, boardHeight, boardWidth);
                printGeneration(board, requestedGenerations, boardHeight, boardWidth);
        }
}
void nextGeneration(state board[][][], int requestedGeneration, int boardHeight, int boardWidth)
{
        int h;
        int w;
        int currentNumOfNeighbours;
        for(h = 0; h < boardHeight; h++)
                for(w = 0; w < boardHeight; w++)
                {
                        currentNumOfNeighbours = numberOfNeighbours(board, requestedGeneration, h, w);
                        if(board[requestedGeneration][h][w] == ALIVE)
                        {
                                if(currentNumOfNeighbours == 2 || currentNumOfNeighbours == 3)
                                        board[requestedGeneration + 1][h][w] == ALIVE;
                        } else if(currentNumOfNeighbours == 3)
                                board[requestedGeneration + 1][h][w] == ALIVE;
                        }
                }
}
int numberOfNeighbours(state board[][][], int requestedGeneration, int h, int w)
{
        int result = 0;
        if(board[requestedGeneration][h][w + 1]) result++;
        if(board[requestedGeneration][h][w - 1]) result++;
        if(board[requestedGeneration][h + 1][w]) result++;
        if(board[requestedGeneration][h - 1][w]) result++;
        if(board[requestedGeneration][h + 1][w + 1]) result++;
        if(board[requestedGeneration][h - 1][w + 1]) result++;
        if(board[requestedGeneration][h + 1][w - 1]) result++;
        if(board[requestedGeneration][h + 1][w - 1]) result++;
        return result;
}
void printGeneration(state board[][][], int requestedGeneration, int boardHeight, int boardWidth)
{
        int h;
        int w;
        for(h = 0; h < boardHeight; h++)
        {
                for(w = 0; w < boardWidth; w++)
                        printf("%d", board[requestedGeneration][h][w]);
                printf("\n");
        }
}

Actual error messages:

program1.c:4: error: array type has incomplete element type
program1.c:5: error: array type has incomplete element type
program1.c:6: error: array type has incomplete element type
program1.c: In function ‘main’:
program1.c:31: error: type of formal parameter 1 is incomplete
program1.c:32: error: type of formal parameter 1 is incomplete
program1.c: At top level:
program1.c:35: error: array type has incomplete element type
program1.c: In function ‘nextGeneration’:
program1.c:43: error: type of formal parameter 1 is incomplete
program1.c: At top level:
program1.c:52: error: array type has incomplete element type
program1.c:65: error: array type has incomplete element type

Any help would be much appreciated, thanks :).

Wait, are you using C99 variable-length arrays or something? Because otherwise I don't think a function can accept a multi-dimensional array parameter with any "unknown" dimension other than the last. — Medinoc
– Medinoc, Commented Apr 18, 2014 at 10:38
@Medinoc So you're saying I should do something like f(state[requestedGenerations][boardHeight][boardWidth] board...)? — shoham
– shoham, Commented Apr 18, 2014 at 10:40

Dabo · Accepted Answer · 2014-04-18 11:26:07Z

2

You need to give size to last two dimensions of array in function definition, something like that for example

     #define y 10
     #define z 10

    void nextGeneration(state board[][y][z], int requestedGeneration, int boardHeight, int boardWidth) 
    {
       ....
    }


    int numberOfNeighbours(state board[][y][z], int requestedGeneration, int h, int w)
    {
       ....
    }

That is to give the system a hint how to calculate the index of an element when you trying to access it. Remember that array (no matter how many dimensions it has) is just a continuous piece of memory, so when you index into your array board[requestedGeneration][h][w] compiler generates code like that

*(board + requestedGeneration * 10 * 10 + h * 10 + w  )

edited Apr 18, 2014 at 11:26

answered Apr 18, 2014 at 10:49

Dabo

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