On 2018-01-23 14:12, Mark Douglas wrote:
Hi Roger,
Thank you very much for this valuable feedback! As I'm new to CMake, I
didn't find the options of disabling char16_t (at least I wasn't
looking for the right thing to start with!).
I think the default policy of using char16_t, if it is available, is a
good choice - cross platform consistency should be maintained where
possible I think. The reason for wanting to use wchar_t is that I'm
moving some legacy code from Xerces C++ 1.5.1 to 3.2.0 and a LOT of
the application code is using wchar_t as the character type. I've also
now selected the VC++ option to 'Treat WChar_t as a Built in Type' in
my application meaning that it's no longer compatible with 16-bit
integer values.
If I were to use char16_t for Xerces C++ I'd need to make a lot of
XMLString::transcode() calls in my application to perform the
conversion. Either that, or I'd have to insert a lot of
reinterpret_cast<wchar_t*> etc. throughout the code. So for me, using
wchar_t seems like the least invasive of the two options and also
means I don't need to perform any transcoding in order to interface
with the rest of the application.
That does sound like a pain and is completely understandable. It's a
shame that they didn't make wchar_t a typedef for char16_t or vice
versa, but I'm sure there were reasons for not doing so. Probably
because the wchar_t encoding is unspecified, and it would also prevent
overloading based on the type if they are the same underlying type.
I think that adding an option to force wchar_t use as you suggest
would be a valuable addition - at least on platform where wchar_t is
16-bit.
I have opened https://issues.apache.org/jira/browse/XERCESC-2132 to
track this. It should be fairly straightforward to add this for 3.2.1.
In the interim, hopefully the edit I suggested will achieve the same
effect by hand with 3.2.0.
By the way, I wasn't quite sure what the CMake '-Dtranscoder=windows'
option did.
It's the default transcoding implementation on Windows using
functionality built into Windows
(src/xercesc/util/Transcoders/Win32/Win32TransService.cpp). You can see
the selection in src/CMakeLists.txt -- search for
XERCES_USE_TRANSCODER_. On Windows, you could use ICU as an
alternative, or GNU iconv if you built it from source. If you wanted
absolutely consistent cross-platform behaviour, then ICU might be a good
choice (I do this for my work projects--we build and use ICU for builds
of Xerces-C++ on all platforms). But the default should be fine in
practice, so you could just leave it unspecified--it should default to
"windows".
Regards,
Roger
