The fstream :: open () Unicode or Non-Ascii characters do not work (with std :: ios :: out) on Windows

In a C ++ project, I want to open file ( fstream::open()) (which seems to be a serious problem). The windows build of my program fails.

• File "ä" (UTF-8 0xC3 0xA4)

  std::string s = ...;
  //Convert s
  std::fstream f;
  f.open(s.c_str(), std::ios::binary | std::ios::in); //Works (f.is_open() == true)
  f.close();
  f.open(s.c_str(), std::ios::binary | std::ios::in | std::ios::out); //Doesn't work
  

  The string sis encoded in UTF-8 encoding, but then converted from UTF-8 to Latin1 (0xE4). I use Qt, therefore QString::fromUtf8(s.c_str()).toLocal8Bit().constData().

  Why can I open a file for reading, but not for writing?

• File and (UTF-8 0xD0 0xB8)

  The same code does not work at all.

This symbol does not seem to fit in the encoding of Windows-1252. How can I open such fstream (I do not use MSVC, therefore nofstream::open(const wchar_t*, ios_base::openmode) )?