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Windows/MinGW extension: opening std::fstream with a wstring/wchar_t*


I have implemented a small patch that mirrors Microsoft's STL
extension, where one can use wide strings as an argument to
std::(w)fstream. This is very useful on Windows, where, without this
extension, there is no way to open an fstream for a filename
containing non-ASCII characters not in the Windows local codepage. The
workaround would be to subclass a streambuf to accept a wchar_t*
filename, but I think a lower-level fix (ie on library level) is much
more suitable, and provides more robustness. In the C API provided by
Microsoft in their MSVCRT (catered for by MinGW(-w64)), a function
_wfopen, which imitates plain fopen, but accepts wchar_t* arguments
for the exact purpose I use it in my patch. Documentation for _wfopen
is here:

No extra #includes are necessary, and for now I #ifdef'ed the extra
code with #if _WIN32. Perhaps cleaner would be a configure check for
OS or CRT used and a __GLIBCXX* macro to enable this functionality.

I understand the patch is not complete (no Changelog, etc...), but I
would like to know your thoughts on how I implemented this
functionality. The changes:
 - libstdc++-v3/config/io/ wfopen_mode: new
function, copy of fopen_mode, but returns wchar_t*
 - libstdc++-v3/config/io/
__basic_file<char>::open: new overload, taking wchar_t* argument, and
uses new wfopen_mode and Windows' _wfopen instead of plain fopen.
 - libstdc++-v3/config/io/basic_file_stdio.h: open: new overload
taking wchar_t* argument
 - libstdc++-v3/include/bits/fstream.tcc: open: new overloads, taking
wchar_t* argument
 - libstdc++-v3/include/std/fstream: open: new overloads taking
wchar_t* and if C++0x is enabled, also overloads taking a std::wstring
 - libstdc++-v3/config/abi/pre/gnu.ver: modify regex statements to
also include new symbols.

Simple testing of the functionality works as it should. I first
modified GCC trunk, created a patch, and applied that to the 4.6
branch. Conclusion: this change should work for GCC 4.6 and up for
sure, maybe even 4.5. As it stands, only Windows is affected, and
should be affected. Perhaps systems where Unicode filenames aren't
UTF-8 (oh wait: that's pretty much Windows only) could also benefit
from this.

Any thoughts/remarks/improvements/commits are very welcome!



Attachment: fstream_wchar_t.patch
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