[tz] Question about bug seen in OpenBSD and FreeBSD related to tzname

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Sat Nov 23 14:50:41 UTC 2019

On 2019-11-23 03:20, Robert Elz wrote:
>     Date:        Sat, 23 Nov 2019 02:52:43 -0500
>     From:        Andras Farkas <deepbluemistake at gmail.com>
>     Message-ID:  <CAA0nTRsAVKLycy=kxt3BMHDv9zmSUEZTMdAbRfO3P+V22aS3vA at mail.gmail.com>
>   | (because it IS the implementation, yet it's also not the OS)
> That distinction, which is made by many standards in various fields
> is totally worthless - whether any particular piece of code (or
> hardware or whatever) is implementation or application (or however
> the relevant standard attempts to divide the world into two groups)
> depends entirely upon where you are looking at it from.

Programmers must clearly distinguish between standard or documented system
independent feature test macros intended to be set by the programmer in
feature_test_macros(7) and the documentation for the system headers, library
interfaces, and standards e.g
	#define _POSIX_C_SOURCE	200809L
	#define _XOPEN_SOURCE	700
	#define	_DEFAULT_SOURCE	1
	#define	_GNU_SOURCE	1
Those feature test macros enable certain features of implementations in
conformance with standards or documentation.

Those standard or documented system independent feature test macros should be
distinguished from implementation specific feature macros often set in
/usr/include/features.h, /usr/include/sys/features.h, and their inclusions,
included from feature test dependent library headers, which may set feature test
macros, and implementation specific feature macros.
Those implementation specific feature macros are tested in library headers in
lieu of various feature test macros e.g. Linux __USE_POSIX, __USE_XOPEN, and
should never be used or set by the programmer as they vary between
implementations and may be changed by any implementation release, as they are
non-standard and undocumented.

Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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