[Bug libstdc++/103655] New: "x" does not exist on windows and dos

[unlvsur at live dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103655

            Bug ID: 103655
           Summary: "x" does not exist on windows and dos
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: unlvsur at live dot com
  Target Milestone: ---

In today's patch.

https://github.com/gcc-mirror/gcc/commit/a219139e986a4200a9105d7c1fa63735d2945994

std::ios::noreplace uses "x". However, that is not correctly supported by
msvcrt and dos djgpp.

The correct way is to directly use CreateFileW (on windows NT) or NtCreateFile
and CreateFileA on windows 9x. Then call _open_osfhandle to create an fd then
call _wfdopen(on windows NT) or _fdopen(on windows 9x) on Windows

Create an NT handle with NtCreateFile (You also need RtlNtStatusToDosError and
RtlDosPathNameToNtPathName_U_WithStatus or RtlDosPathNameToNtPathName_U).

https://github.com/tearosccebe/fast_io/blob/6081ae18b34820c3c69b81628f520f5fafcfb815/include/fast_io_hosted/platforms/nt.h#L67

Or create a win32 handle with CreateFileA (on Windows 9x) and CreateFileW (on
Windows NT)

https://github.com/tearosccebe/fast_io/blob/6081ae18b34820c3c69b81628f520f5fafcfb815/include/fast_io_hosted/platforms/win32.h#L201

Use win32 or nt handle to call _open_osfhandle to create a POSIX fd.

https://github.com/tearosccebe/fast_io/blob/6081ae18b34820c3c69b81628f520f5fafcfb815/include/fast_io_hosted/platforms/posix.h#L58

https://github.com/tearosccebe/fast_io/blob/6081ae18b34820c3c69b81628f520f5fafcfb815/include/fast_io_hosted/platforms/posix.h#L961

Then use _wfdopen on Windows NT and _fdopen on Windows 9x to open a FILE*

https://github.com/tearosccebe/fast_io/blob/6081ae18b34820c3c69b81628f520f5fafcfb815/include/fast_io_legacy_impl/c/impl.h#L29

Then construct a std::filebuf with FILE*

https://github.com/tearosccebe/fast_io/blob/6081ae18b34820c3c69b81628f520f5fafcfb815/include/fast_io_legacy_impl/filebuf/filebuf_file.h#L60


On DOS. You need __dos_creat,__dos_creatnew,__dos_open
https://github.com/tearosccebe/fast_io/blob/6081ae18b34820c3c69b81628f520f5fafcfb815/include/fast_io_hosted/platforms/posix.h#L1063


So libstdc++ using fdopen to open FILE* with fd is incorrect. On windows NT
kernel, we MUST use _wfdopen since _fdopen involves locale, which is not
thread-safe.