Function mb_to_utf8

crawl-ref/source/unicode.cc:218–249

}

string mb_to_utf8(const char *s)
{
#ifdef __ANDROID__
    // Paranoia; all consumers already use the same code so this won't do
    // anything new.
    return utf8_validate(s);
#else
    string d;
    wchar_t c;
    int l;
    mbstate_t ps;

    memset(&ps, 0, sizeof(ps));
    // the input is zero-terminated, so third argument doesn't matter
    while ((l = mbrtowc(&c, s, MB_LEN_MAX, &ps)))
    {
        if (l > 0)
            s += l;
        else
        {   // invalid input, mark it and try to recover
            s++;
            c = 0xFFFD;
        }

        char buf[4];
        int r = wctoutf8(buf, c);
        for (int i = 0; i < r; i++)
            d.push_back(buf[i]);
    }
    return d;
#endif
}

static bool _check_trail(FILE *f, const char* bytes, int len)
{