template <int N>
struct s_str_sbuilder
{
    static_assert(N > 0);
    int len = 0;
    int max_chars = N;
    char data[N + 1];

    char* cstr()
    {
        assert(len > 0);
        return data;
    }

    char* get_end_ptr()
    {
        return &data[len];
    }

    void append(char* format, ...)
    {
        char* where_to_write = &data[len];
        va_list args;
        va_start(args, format);
        int written = vsnprintf(where_to_write, max_chars + 1 - len, format, args);
        assert(written > 0 && written < max_chars);
        va_end(args);
        len += written;
        data[len] = 0;
    }

    void remove_last_char()
    {
        assert(len > 0);
        len -= 1;
        data[len] = 0;
    }
};