Variable length array as function parameter, casted before passing, using GNU C forward parameter declaration

vla-forward.c

// compile me with `gcc -std=c99` or `gcc -std=gnu99`

#include <stdio.h>

int sum(int n_col; int arr[][n_col], int n_row, int n_col) {
    int i, j, total = 0;
    for (i = 0; i < n_row; ++i) {
        for (j = 0; j < n_col; ++j) {
            total += arr[i][j];
        }
    }
    return total;
}

int main(int argc, char *argv[]) {
    int n_col = 5, n_row = 5;
    int arr[25];

    int i, j;
    for (i = 0; i < n_row; ++i) {
        for (j = 0; j < n_col; ++j) {
            arr[i * n_col + j] = 1;
        }
    }

    printf("%d\n", sum((int (*)[n_col])arr, n_row, n_col));
    return 0;
}