Why isn't UTF-8 allowed as the “ANSI” code page?

Question

The Windows _setmbcp function allows any valid code page...

(except UTF-7 and UTF-8, which are not supported)

OK, not supporting UTF

Answer 1

_setmbcp() is a VC++ RTL function, not a Win32 API function. It only affects how the RTL interprets strings. It has no effect whatsoever on Win32 API A functions. When they call their W counterparts internally, the A functions always use MultiByteToWideChar() and WideCharToMultiByte() specifying codepage 0 (CP_ACP) to use the system default Ansi codepage for the conversions.