Question

I’ve created an app to solve sudoku grids…but
here is my problem : my app has some bug and even crashes with my Distribution Configuration for compiling (equivalent to Release Configuration).

Here is the code where it bugs :

- (int*)completeNb:(int[9][9])aMatrix {
    int n, nb;
    int cell[2];
    int *pcell;
    BOOL found = FALSE;
    BOOL pos = FALSE;
    for (int k = 1; k <= 9; k++) {
        n = 0;
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (aMatrix[i][j] == k)
                    n++;
            }
        }
        if (n == 8) {
            found = TRUE;
            nb = k;
            break;
        }
    }
    if (found) {
        for (int l = 0; l < 9; l++) {
            for (int m = 0; m < 9; m++) {
                if ([self isPossibleValue:aMatrix value:nb line:l column:m]) {
                    cell[0] = l;
                    cell[1] = m;
                    pos = TRUE;
                    break;
                }
            }
            if (pos)
                break;
        }
        pcell = cell;
    }
    else {
        pcell = nil;
    }
    return pcell;
}

I have a special sudoku grid where I should find {6,6} as the right position for number 6 (6 should at i=6 and j=6 in the grid). It works perfectly in Debug Configuration, but with Distrib Conf, it seems like I have problem with the l and m vars -> the loop breaks well at l=6 and m=6 (hence, isPossibleValue function seems to work well), but then my cell variable is equal to {1;0}, instead of {6;6} !

I am using this kind of process (returning a cell[2]) with many other functions, and I don’t have any problem with the Distrib Conf.

My second problem, – and this one is provoking the app to crash – is with the following code (again, perfectly working with debug configuration).

- (void)solver:(int[9][9])aMatrix {
    if (!Termine) {
        int *emptyCell = [self firstEmptyCell:aMatrix];
        if (emptyCell != nil) {
            int i = emptyCell[0];
            int j = emptyCell[1];
            for (int k = 1; k <= 9; k++) {
                if ([self isPossibleValue:aMatrix value:k line:i column:j]) {
                    aMatrix[i][j] = k;
                    [self solver:aMatrix];
                    aMatrix[i][j] = 0;
                }
            }
        }
        else {
            if (!Termine) {
                Termine = TRUE;
                for (int i = 0; i < 9; i++)
                    for (int j = 0; j < 9; j++)
                        res[i][j] = aMatrix[i][j];
            }
        }

    }
}

Note : one solution, – I am not sure that’s the best one – is to change optimization level from “fastest, smallest” to “none”.

Thanks for your help !

Answer 1

For the first case the problem is in int cell[2];. It has a local scope, and after you return from the function the memory zone pointed by this array very likely will be reallocated for other needs. A quick solution is to add static specifier:

static int cell[2];

For the second snippet, make sure that emptyCell each time assigns to i and j values which doesn’t exceed aMatrix bounds [0..8][0..8].