Windows API ANSI functions and UTF-8

Question

Is it possible to use Windows API ANSI functions with UTF-8 strings?

For example, say I have a path encoded in UTF-8. Can I call CreateDirectoryA or CreateFileA and use a UTF-8 path, or do I have to perform some conversion before calling the functions?

Answer 1

No. Use MultiByteToWideChar to convert UTF-8 to UTF-16 and then call the wide character APIs such as CreateDirectoryW or CreateFileW.

Answer 2

An easier approach (than using raw Win32 API MultiByteToWideChar) would be to use ATL conversion helpers, like CA2CW. You can specify CP_UTF8 as code page (second parameter in the constructor), to convert from Unicode UTF-8 to Unicode UTF-16:

CreateDirectoryW( 
  CA2W( utf8Name, CP_UTF8 ) // convert from UTF-8 to UTF-16
  ... // other stuff
);

Note that in Unicode builds (which should be the default ones these days), CreateDirectory just expands to CreateDirectoryW, so I would just drop the ending "W" and use the (IMHO, more readable) CreateDirectory:

CreateDirectory( 
  CA2W( utf8Name, CP_UTF8 ) // convert from UTF-8 to UTF-16
  ... // other stuff
);

Answer 3

The accepted answer is no longer correct (as of Windows Version 1903 (May 2019 Update)).

An application can now set the active code page of the process to UTF-8. This allows ...A functions (and CP_ACP) to work with UTF-8. A manifest to do that looks like this

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1">
  <assemblyIdentity type="win32" name="..." version="6.0.0.0"/>
  <application>
    <windowsSettings>
      <activeCodePage xmlns="http://schemas.microsoft.com/SMI/2019/WindowsSettings">UTF-8</activeCodePage>
    </windowsSettings>
  </application>
</assembly>

Source and additional information: Use the Windows UTF-8 code page