Accessing an Element from an int ** array in C++

Question

I am creating a 2D-Array in C++ and need to pass this array as a parameter in a function. In my function, I need to access an element from the array in order to save it as a value, ie:

int lowestPoint(int **arr, int x, int y, int n) {

    minVal = *(*(arr+x)+y); // here is where I'm getting the exception
    return minVal;

}

I've tried setting minVal to arr[X][Y] and have tried to pass the array in as other variations instead of just **arr but nothing seems to be working.

The array is initialized in my main function as int arr[x][y] and I pass it into another function by casting it as otherFunc(reinterpret_cast<int **>((*arr)[n]), n) , and then from that function, send it to lowestPoint by calling int val = lowestPoint(arr,i,j,n) . I think these calls could be problematic but I'm uncertain how to fix it - I really have no experience with 2D arrays in C++ and it's soo much simpler in Java. I keep getting an EXC_BAD_ACCESS error for the array, so if anyone has any idea how to fix that, I'd really appreciate it. Thanks!

EDIT: "n" is the size of the array; for example if it's a 3x3 array, n = 3. I just initialized the array as int arr[n][n] and then stored elements. I know the actual array itself represents the correct value, it just can't access it once I send it to another function.

Answer 1

When you pass the array to the first function using reinterpret_cast((*arr)[n]), instead of passing the pointer to the actual array, you are passing the value in location [0][n] (by using (*arr)[n]) and casting it to **arr. So in essence you get a new array that points to a random location in memory that is equal to the content of that array slot.

I am not sure what you intended to do, but if you wanted to pass the actual array, just pass arr. If you planned to pass a sub-array, this method is incorrect altogether as you pass an offset inside an array and you will get skewed data.

Hope This helps, Lior