int find_node(table_of_sons *children, const wchar_t letter)
{
    size_t start = 0;
    size_t check;
    size_t end = children->size-1;
    while (start < end)
    {
        check = (start+end)/2;
        if (wcscoll(&letter, &children->nodes[check]->letter) > 0)
            start = check+1;
        else
            end = check;
    }
    if (wcscoll(&children->nodes[check]->letter, &letter) == 0)
        return start;
    else
        return -1;
}