c++ - Handling UTF-8 encoded strings between std::wstring and std::string

Question

I am using two libraries one that stores UTF-8 strings in std::wstring and another stores strings ( UTF-8) in std::string.
What is the best / efficient method I can use to pass strings between the two libraries.
I am currently on Windows using Visual C++ v9 Express but would prefer a portable solution.

Answer 1

Assuming you mean UTF-16 and not UTF-8 for std::wstring, you will have to encode/decode the strings from one library to the other. I'm not sure if/what the STL provides for that, but you can use Windows's own MultiByteToWideChar() and WideCharToMultiByte() functions to convert between UTF-8 and UTF-16 with just a few lines of code. You could then wrap that into your own functions so you can replace the logic when you find something more portable, eg:

std::wstring Utf8ToUtf16(const std::string &s)
{
    std::wstring ret;
    int len = MultiByteToWideChar(CP_UTF8, 0, s.c_str(), s.length(), NULL, 0);
    if (len > 0)
    {
      ret.resize(len);
      MultiByteToWideChar(CP_UTF8, 0, s.c_str(), s.length(), const_cast<wchar_t*>(ret.c_str()), len);
    }
    return ret;
}

std::string Utf16ToUtf8(const std::wstring &s)
{
    std::string ret;
    int len = WideCharToMultiByte(CP_UTF8, 0, s.c_str(), s.length(), NULL, 0, NULL, NULL);
    if (len > 0)
    {
      ret.resize(len);
      WideCharToMultiByte(CP_UTF8, 0, s.c_str(), s.length(), const_cast<char*>(ret.c_str()), len, NULL, NULL);
    }
    return ret;
}