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

Steffen Nurpmeso steffen at sdaoden.eu
Sat Nov 23 19:48:04 UTC 2019

Brian Inglis wrote in <f5634d94-4b76-5852-316d-a634d7191ae8 at SystematicSw\
 |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 mai\
 |>     l.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, \
 |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.

Since you refer to feature_test_macros(7) i want to add that
i find headers of especially elder systems notoriously buggy
regarding the above.  One should especially not trust statements
like "defining x produces the same effects as defining y".  I am
in the lucky position to be able to test on several operating
systems, and thanks to OpenCSW.org this also includes SunOS 5.9 -
5.11.  My findings are that you are best served with
a sledgehammer by defining all of the above (i do except
_DEFAULT_SOURCE), and i also still have a _DARWIN_C_SOURCE
lingering even though the last i tested was Mountain Lion.  (But
it still works like this out of the box as of today via Homebrew
and MacPorts.)

 |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, \
 |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.

|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)

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