Help with cross-platform wchar_t to utf8 conversion

[David Bruce]

Hi,

I'm the upstream maintainer for Tux Math and Tux Typing.  I just
contributed a current portfile for tuxmath, and would like to add
tuxtype as well.  The tuxtype port is almost ready to go, but a
significan part of the game doesn't work because the existing code to
convert a wchar_t string to utf8 doesn't work as built by macports.

Tuxtype is a C program that uses SDL, without any Mac-specific
libraries.  The existing conversion uses iconv, with a check to take
into account Microsoft's two-byte wchar_t.  I had assumed the Mac
would work just like Linux in this regard, but so far it hasn't.

The relevant OS-specific part works like this:

 //Microsoft uses a different wchar_t from the rest of the world - grrr...
#ifdef WIN32
 DEBUGCODE {fprintf(stderr, "WIN32, using UTF-16LE for wchar_t\n");}
 conv_descr = iconv_open("UTF-8", "UTF-16LE");
#else
 conv_descr = iconv_open("UTF-8", "UTF-32");
#endif

 bytes_converted = iconv(conv_descr,
                         &wchar_t_Start, &in_length,
                         &UTF8_Start, &out_length);

and so forth.

On Mac, the UTF-32 version gets selected, but it doesn't work.

So, as a quick fix:
1. is a Mac wchar_t string UTF-32BE, UTF-32LE, or something else?
2. what is the best preprocessor symbol to test for (i.e. __APPLE__,
MACOSX, etc) to know if we are building for the Mac?  This same code
may also be built with CMake.

I realize that in the long run it is better to get away from wchar_t,
and that it is generally better to test directly for features a la
Autoconf rather than just checking for a platform symbol.  But if
anyone knows these details offhand, I could have a functioning tuxtype
port tonight.

Thanks for any help,

David Bruce

(p.s. I tried to send this to the list about an hour ago and got a
bounce - I apologize if you got a duplicate)