Are BSTR UTF-16 Encoded?

Question

I'm in the process of trying to learn Unicode? For me the most difficult part is the Encoding. Can BSTRs (Basic String) content code points U+10000 or higher? If no, then what's the encoding for BSTRs?

Answer 1

In Microsoft-speak, Unicode is generally synonymous with UTF-16 (little endian if memory serves). In the case of BSTR, the answer seems to be it depends:

• On Microsoft Windows, consists of a string of Unicode characters (wide or double-byte characters).
• On Apple Power Macintosh, consists of a single-byte string.
• May contain multiple embedded null characters.

So, on Windows, yes, it can contain characters outside the basic multilingual plane but these will require two 'wide' chars to store.

Answer 2

BSTR's on Windows originally contained UCS-2, but can in principle contain the entire unicode set, using surrogate pairs. UTF-16 support is actually up to the API that receives the string - the BSTR has no say how it gets treated. Most API's support UTF-16 by now. (Michael Kaplan sorts out the details.)

The windows headers still contain another definition for BSTR, it's basically

#if defined(_WIN32) && !defined(OLE2ANSI)
   typedef wchar_t OLECHAR;
#else
   typedef char OLECHAR;
#endif
typedef OLECHAR * BSTR;

There's no real reason to consider the char, however, unless you desperately want to be compatible with whatever this was for. (IIRC it was active - or could be activated - for early MFC builds, and might even have been used in Office for Mac or something like that.)