Как изменить кодировку для записи в файл

String pMessage

FILE *LogFile=_tfopen(mLogDirectionFilePath.c_str(),_T("a"));
_ftprintf(LogFile,MessageString.c_str());

_ftprintf(LogFile,(L"Проверка\n"));
_ftprintf(LogFile,_T("Проверка\n"));

#define _ftprintf       fwprintf

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    String mLogDirectionFilePath = L"D:\\test\\mylog01.txt";
    String MessageString = L"Просто тест";
 
    int fsMode = FileExists(mLogDirectionFilePath) ? fmOpenReadWrite : fmCreate;
 
    std::auto_ptr<TFileStream> log(new TFileStream(mLogDirectionFilePath, fsMode, fmShareDenyWrite));
    RawByteString outpututf8 = UTF8Encode(MessageString);
    if (fsMode == fmCreate)
    {
        TBytes preamble = TEncoding::UTF8->GetPreamble();
        log->WriteBuffer(&preamble[0], preamble.Length);
    }
    else
        log->Seek(log->Size, 0);
 
    outpututf8 = outpututf8 + "\r\n"; // char(13) + char(10);
    log->WriteBuffer(&outpututf8[1], outpututf8.Length());
}

setlocale(LC_ALL, "Russian");

        std::ofstream os("c:\\temp\\test.txt");
        os << "йцуке";
        os.close();