Feature Conditional for M_PI

[Corinna Vinschen]

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.
> 
> In glibc's math.h, M_PI is guarded with
> 
>   #if defined __USE_MISC || defined __USE_XOPEN
> 
> In newlib, it's guarded with
> 
>   #if __BSD_VISIBLE || __XSI_VISIBLE
> 
> Note that this is identical to the guards on at least FreeBSD.
> 
> In both cases, newlib as well as glibc, "MISC" is defined by default,
> but "BSD" isn't.  That's why your 3rd invocation fails on BSDs and
> newlib/Cygwin, but not on Linux.

Huh, wait!  I bet this does *not* fail on BSD because BSD very likely
defines __BSD_VISIBLE by default.

We could move the math.h constants to __MISC_VISIBLE || __XSI_VISIBLE,
perhaps that makes more sense for us?


Corinna