[Mingw-users] best value for guarding MinGW patches

Eli Zaretskii

2017-05-01 06:45:32 UTC

Date: Sun, 30 Apr 2017 19:28:15 -0500
I have been doing test builds of the gcc 7 release candidates and
have found and fixed a problem in the c++ run-time library that
crashes the build.
I want to submit a patch to the upstream gcc that will
A: isolate the MinGW-specific patch from other build environments
and
B: not require any modifications/improvements by the upstream
gcc crew, as that would almost certainly mean that it would not
get into the upcoming release.
What is the best #ifdef or #if defined value that I can use for this?
In some of the patches used for the current MinGW gcc 5.3.0,
I see
#if defined(_WIN32)
Should I go with this or is there a better one?

It depends, but in general, _WIN32 would not by my first choice, for
the simple reason that it also includes Cygwin, which you probably
don't want. It also includes MSVC builds, although in this case that
possibility is not relevant.

My first choice would be

#ifdef __MINGW32__

However, there could be complications if the problem you've discovered
is specific to mingw.org's MinGW, and the solution should NOT affect
the MinGW64 build of GCC (because, sadly, their headers and runtime
diverged in subtle but significant ways from mingw.org). If that is
the case, you will need something more elaborate. I'm using this:

#ifdef __MINGW32__
# include <_mingw.h>
# ifndef __MINGW64_VERSION_MAJOR
# ...mingw.org's MinGW stuff...
# endif
#endif

This ugliness is required because MinGW64 doesn't provide any
preprocessor facilities to distinguish it from mingw.org that could be
used without including some standard header file, and they also define
__MINGW32__, so that macro cannot be used for this purpose.

HTH

P.S. Thank you for working on GCC 7; I hope to see its official MinGW
build on a download site near me, soon.

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