From: Corinna Vinschen <vinschen@redhat.com>
To: newlib@sourceware.org
Subject: Re: Feature Conditional for M_PI
Date: Mon, 31 Aug 2020 22:04:56 +0200 [thread overview]
Message-ID: <20200831200456.GI3272@calimero.vinschen.de> (raw)
In-Reply-To: <CAF9ehCX+2xMDi4FvYpKqYEATyTthkmNNAcHrkS_8nO_y8juGDg@mail.gmail.com>
On Aug 31 10:50, Joel Sherrill wrote:
> On Mon, Aug 31, 2020 at 10:30 AM Corinna Vinschen via Newlib <
> newlib@sourceware.org> wrote:
>
> > On Aug 31 17:27, Corinna Vinschen via Newlib wrote:
> > > On Aug 31 10:10, Joel Sherrill wrote:
> > > > Hi
> > > >
> > > > I was porting some code from Linux to Cygwin and came across this.
> > M_PI in
> > > > math.h is defined by POSIX as part of XSI. It does not appear to be
> > part of
> > > > C99 or C++03. I have this cut down to show the problem:
> > > >
> > > > ==========================
> > > > #include <math.h>
> > > >
> > > > double pi = M_PI;
> > > > ==========================
> > > >
> > > > And this script to try various feature defines and compilers:
> > > >
> > > > ===========================
> > > > GCC=${GCC:-g++}
> > > >
> > > > ${GCC} -c m.c
> > > > ${GCC} -D_XOPEN_SOURCE=700 -c m.c
> > > > ${GCC} -D_POSIX_C_SOURCE=200809L -c m.c
> > > > ${GCC} -D_XOPEN_SOURCE=700 -c -D_POSIX_C_SOURCE=200809L -c m.c
> > > > ===========================
> > > >
> > > > All of those compiler invocations work on Linux but the third one does
> > not
> > > > work on Cygwin or RTEMS which use newlib.
> > > >
> > > > Is the proper thing to do to add -D_XOPEN_SOURCE=700 when compiling
> > this
> > > > program?
> > > >
> > > > Just curious if Linux is defining _XOPEN_SOURCE by default and newlib
> > > > doesn't.
Actually, Yaakov pointed out on IRC that this is a C++ problem on Linux.
You're running the above test with g++. If you perform the third test
with gcc on Linux:
gcc -D_POSIX_C_SOURCE=200809L -c m.c
you'll get the same error as on newlib and FreeBSD:
m.c: In function ‘main’:
m.c:8:15: error: ‘M_PI’ undeclared (first use in this function)
8 | double pi = M_PI;
| ^~~~
m.c:8:15: note: each undeclared identifier is reported only once for each function it appears in
The problem in glibc and/or g++ is that this does *not* occur when
building with g++.
Corinna
next prev parent reply other threads:[~2020-08-31 20:05 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-31 15:10 Joel Sherrill
2020-08-31 15:27 ` Corinna Vinschen
2020-08-31 15:29 ` Corinna Vinschen
2020-08-31 15:50 ` Joel Sherrill
2020-08-31 20:04 ` Corinna Vinschen [this message]
2020-08-31 21:19 ` Joel Sherrill
2020-09-01 2:04 ` Yaakov Selkowitz
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