UTF-8 in Windows

Unfortunately, there is no way to make Unicode the current codepage in Windows. The CP_UTF7 and CP_UTF8 constants are pseudo-codepages, used only in MultiByteToWideChar and WideCharToMultiByte conversion functions, like Ben mentioned.

Your problem is similar to that of the fstream C++ classes. The fstream constructors accept only char* names, making impossible to open a file with a true Unicode name. The only solution offered by VC was a hack: open the file separately and then set the handle to the stream object. I'm afraid this isn't an option for you, of course, since the third party library probably doesn't accept handles.

The only solution I can think of is to create a temporary file with a non-Unicode name, which is hard-linked to the original, and use that as a parameter.

All Windows APIs think in UTF-16, so you're better off writing a wrapper around your library that converts at the boundaries.

Oddly enough, Windows thinks UTF-8 is a codepage for the purposes of conversion, so you use the same APIs as you would to convert between codepages:

std::wstring Utf8ToUtf16(const char* u8string){    int wcharcount = strlen(u8string);    wchar_t *tempWstr = new wchar_t[wcharcount];    MultiByteToWideChar(CP_UTF8, 0, u8string, -1, tempWstr, wcharcount);    wstring w(tempWstr);    delete [] tempWstr;    return w;}

And something of similar form to convert back.

2018 update: Windows 10 has made the "65001" code page less "pseudo" in two steps:

1. conhost changes: Windows Subsystem for Linux uses code page 65001 for its consoles. It is also possible to run chcp 65001 in cmd.exe since WSL. (It has caused some pretty dumb Python bugs.)
2. full-featured locale: Windows since build 17035 allows setting UTF-8 as the locale codepage. This is available from the April 2018 update.