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From: "i at maskray dot me" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107543] New: c-family/c-cppbuiltin.cc: Undefine
 __GNUC_STDC_INLINE__ in C++ mode?
Date: Sun, 06 Nov 2022 21:39:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107543

            Bug ID: 107543
           Summary: c-family/c-cppbuiltin.cc: Undefine
                    __GNUC_STDC_INLINE__ in C++ mode?
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: i at maskray dot me
  Target Milestone: ---

-fgnu89-inline / C99 / C++  inline modes are all different. For C++, perhaps
neither=20
__GNUC_STDC_INLINE__ nor __GNUC_GNUC_INLINE__ should be defined.

% g++ -dM -E -xc++ /dev/null | grep __GNUC_STDC_INLINE__
#define __GNUC_STDC_INLINE__ 1


gcc/doc/cpp.texi does not talk about C++

@item __GNUC_STDC_INLINE__
GCC defines this macro if functions declared @code{inline} will be
handled according to the ISO C99 or later standards.  Object files will con=
tain
externally visible definitions of all functions declared @code{extern
inline}.  They will not contain definitions of any functions declared
@code{inline} without @code{extern}.

If this macro is defined, GCC supports the @code{gnu_inline} function
attribute as a way to always get the gnu90 behavior.


Side note: there is "warning: command-line option =E2=80=98-fgnu89-inline=
=E2=80=99 is valid for
C/ObjC but not for C++" but  __attribute__((gnu_inline)) is usable in C++ m=
ode
and has strange codegen behaviors.=