C Multi-Dimensional Array With Indexing Function

multi_dim_array_idx.c

void *array_alloc(int ndims, const int dims[ndims], int size) {
    int n = 1;
    for(int i = 0; i < ndims; i += 1)
        n *= dims[i];
    return calloc(n, size);
}

int array_idx(int ndims, const int dims[ndims], const int idx[ndims]) {
    int i = 0, s = 1;
    for(int j = ndims - 1; j >= 0; j -= 1)
        i += idx[j] * s, s *= dims[j];
    return i;
}

int main() {
    const int X = 5, Y = 2, Z = 3, W = 2;
    int *mat = array_alloc(4, (int[4]){X, Y, Z, W}, sizeof(int));
    int mat4121 = mat[array_idx(4, (int[4]){X, Y, Z, W}, (int[4]){4, 1, 2, 1})];
    // Or define a macro
    #define I5232(mat, x, y, z, w) mat[array_idx(4, (int[4]){5, 2, 3, 2}, (int[4]){x, y, z, w})]
    int mat4111 = I5232(mat, 4, 1, 1, 1);
    // ...
    free(mat);
}