Function unique_path

src/unique_path.cpp:308–345

#endif // defined(linux) || defined(__linux) || defined(__linux__)

BOOST_FILESYSTEM_DECL
path unique_path(path const& model, system::error_code* ec)
{
    // This function used wstring for fear of misidentifying
    // a part of a multibyte character as a percent sign.
    // However, double byte encodings only have 80-FF as lead
    // bytes and 40-7F as trailing bytes, whereas % is 25.
    // So, use string on POSIX and avoid conversions.

    path::string_type s(model.native());

    char ran[16] = {};                                                    // init to avoid clang static analyzer message
                                                                          // see ticket #8954
    BOOST_CONSTEXPR_OR_CONST unsigned int max_nibbles = 2u * sizeof(ran); // 4-bits per nibble

    unsigned int nibbles_used = max_nibbles;
    for (path::string_type::size_type i = 0, n = s.size(); i < n; ++i)
    {
        if (s[i] == percent) // digit request
        {
            if (nibbles_used == max_nibbles)
            {
                system_crypt_random(ran, sizeof(ran), ec);
                if (ec && *ec)
                    return path();
                nibbles_used = 0;
            }
            unsigned int c = ran[nibbles_used / 2u];
            c >>= 4u * (nibbles_used++ & 1u); // if odd, shift right 1 nibble
            s[i] = hex[c & 0xf];              // convert to hex digit and replace
        }
    }

    if (ec)
        ec->clear();

    return s;
}

} // namespace detail
} // namespace filesystem