How do I convert a string in UTF-16 to UTF-8 in C++

Question

Consider:

STDMETHODIMP CFileSystemAPI::setRRConfig( BSTR config_str, VARIANT* ret )
{
mReportReaderFactory.reset( new sbis::report_reader::ReportReaderFactory() );

USES_CONVERSION;
std::string configuration_str = W2A( config_str );

But in config_str I get a string in UTF-16. How can I convert it to UTF-8 in this piece of code?

Answer 1

You can do something like this

std::string WstrToUtf8Str(const std::wstring& wstr)
{
  std::string retStr;
  if (!wstr.empty())
  {
    int sizeRequired = WideCharToMultiByte(CP_UTF8, 0, wstr.c_str(), -1, NULL, 0, NULL, NULL);

    if (sizeRequired > 0)
    {
      std::vector<char> utf8String(sizeRequired);
      int bytesConverted = WideCharToMultiByte(CP_UTF8, 0, wstr.c_str(),    
                           -1, &utf8String[0], utf8String.size(), NULL, 
                           NULL);
      if (bytesConverted != 0)
      {
        retStr = &utf8String[0];
      }
      else
      {
        std::stringstream err;
        err << __FUNCTION__ 
            << " std::string WstrToUtf8Str failed to convert wstring '"
            << wstr.c_str() << L"'";
        throw std::runtime_error( err.str() );
      }
    }
  }
  return retStr;
}

You can give your BSTR to the function as a std::wstring