[Insight-developers] Unicode filenames, VS6 and fdstream (was:Unicode filenames and borland issue)

[Tom Vercauteren]

Hi Bill,

Thanks for taking a look at this!

Are the problems you found related to the use of _wfopen and _wopen or
to the use of fdstream? This is an important distinction for the
unicode filename porting because the plan I had in mind relies on
fdstream being used in all cases (ITK_USE_REVIEW_UTF8_STRINGS on or
off).

Indeed here is what I found (VS6 not taken into account here):

1) c-style file IO can be ported relatively easily to utf8 on windows
(msvc, borland, mingw). Just replace fopen by _wfopen and open by
_wopen together with some string conversion

2) c++-style IO is more involved. There is a wide string version of
ofstream.open() and ifstream.open() on msvc but not on mingw (did not
try with on borland).

Since the fstreams cannot be opened with a unicode filename on mingw,
the workaround is to open the file using c-style functions and then
create a stream from the result of the c-style open.

A gcc specific extension exists for that (stdio_filebuf) but it is
obviously non-portable. fdstream does the same thing but appeared to
be portable.

So to get unicode filename enabled streams, we need to replace code like

A)
std::ifstream readstream(filename, std::ios::binary | std::ios::in)

by code like

B)
int fd = _wopen(filename, _O_RDONLY);
boost::fdistream readstream(fd);
[...]
close(fd)

We might of course pepper the code with ifdefs each time a stream is
used (as is already done to workaround a sgi bug in metaImage.cxx
http://public.kitware.com/cgi-bin/viewcvs.cgi/Utilities/MetaIO/metaImage.cxx?root=Insight&view=markup
) but I wanted to avoid that by restricting these ifdefs to live in a
specified file/module. Hence my plan to wrap only the c-style (f)open
functions and use fdstreams everywhere.

Note that since we need to close the file descriptor and because
fd(i/o)streams do not inherit from (i/o)fstream but only from
(i/o)stream, it is not obvious to have a function that uses either the
A mode or B mode above.

Sorry for this long email,
Tom

P.S.: some information is also available on the bug tracker:
http://public.kitware.com/Bug/view.php?id=9623

On Tue, Nov 10, 2009 at 21:11, Bill Lorensen <bill.lorensen at gmail.com> wrote:
> My first try with VS6 is not encouraging. I suggest that we instrument
> the code so that VS6 ITK cannot use Unicode.