Use of #if DEBUG in reent.h

Corinna Vinschen
Mon Jan 9 15:23:00 GMT 2017



On Jan  3 16:41, Joe Seymour wrote:
> Users can enable assertions in newlib/libc/include/sys/reent.h by
> defining the macro DEBUG. As DEBUG is a relatively obvious and general
> purpose name, it is also used by other projects. I've seen it used by
> the Atmel Software Framework (ASF) and some TI Energia projects.  A web
> search finds a few more examples:
> Actually, these are all examples of projects that have been seen to fail
> to build with the following error:
> > include\sys\reent.h:458:10: error: #if with no expression
> This occurs when DEBUG is defined but has no value. Which seems to
> happen with the following test case:
> > #define DEBUG
> > #include <sys/reent.h>
> Notably, I don't see an error if I remove the #define and instead pass
> -DDEBUG (with no value) to my gcc build [msp430-elf-gcc (GCC) 7.0.0
> 20161220].
> My initial reaction to seeing the error message was that this was a bug
> in reent.h, which should use #ifdef DEBUG instead. Unfortunately if you
> do that then "#define DEBUG 0" and -DDEBUG=0 result in debug being
> turned on, which seems undesirable. This leads me to believe that the
> use of #if DEBUG is deliberate and not considered a bug?
> I mention this here because I couldn't find any previous discussion of
> it on this list, and as it has been discussed elsewhere I think there's
> value in having a definitive statement about it here.
> Again for the record, I'll ask whether "#if DEBUG" could be changed to
> "#if _SYS_REENT_H_DEBUG", or similar? That would avoid the error and the
> naming conflict.  I'm assuming that the examples listed above aren't
> trying to turn newlib assertions on. I suspect that at the very least
> DEBUG has been used for long enough that there's a stronger argument for
> keeping it the same than for changing it to something else?
> Thanks,
> Joe Seymour

Corinna Vinschen
Cygwin Maintainer
Red Hat
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