[PATCH] tzset: update doc for TZ problems on MS-Windows

[Paul Eggert]

* doc/posix-functions/ctime.texi,  doc/posix-functions/daylight.texi:
* doc/posix-functions/localtime.texi, doc/posix-functions/mktime.texi:
* doc/posix-functions/strftime.texi, doc/posix-functions/timezone.texi:
* doc/posix-functions/tzname.texi, doc/posix-functions/tzset.texi:
* doc/posix-functions/wcsftime.texi:
Mention some issues with TZ under MS-Windows.
---
 ChangeLog                          | 10 ++++++++++
 doc/posix-functions/ctime.texi     |  3 +++
 doc/posix-functions/daylight.texi  |  6 ++++++
 doc/posix-functions/localtime.texi |  3 +++
 doc/posix-functions/mktime.texi    |  3 +++
 doc/posix-functions/strftime.texi  |  3 +++
 doc/posix-functions/timezone.texi  |  6 ++++++
 doc/posix-functions/tzname.texi    |  6 ++++++
 doc/posix-functions/tzset.texi     |  9 +++++++++
 doc/posix-functions/wcsftime.texi  |  3 +++
 10 files changed, 52 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index c9b6146..ad44003 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2017-05-01  Paul Eggert  <address@hidden>
+
+       tzset: update doc for TZ problems on MS-Windows
+       * doc/posix-functions/ctime.texi,  doc/posix-functions/daylight.texi:
+       * doc/posix-functions/localtime.texi, doc/posix-functions/mktime.texi:
+       * doc/posix-functions/strftime.texi, doc/posix-functions/timezone.texi:
+       * doc/posix-functions/tzname.texi, doc/posix-functions/tzset.texi:
+       * doc/posix-functions/wcsftime.texi:
+       Mention some issues with TZ under MS-Windows.
+
 2017-05-01  Bruno Haible  <address@hidden>
 
        copy-file: Fix build error on mingw.
diff --git a/doc/posix-functions/ctime.texi b/doc/posix-functions/ctime.texi
index 6abc4c4..7294f33 100644
--- a/doc/posix-functions/ctime.texi
+++ b/doc/posix-functions/ctime.texi
@@ -24,6 +24,9 @@ typically write the timestamp into static buffer.  If two 
threads
 call @code{ctime} at roughly the same time, you might end up with the
 wrong date in one of the threads, or some undefined string.  There is
 a re-entrant interface @code{ctime_r}.
address@hidden
+Native Windows platforms (mingw, MSVC) support only a subset of time
+zones supported by GNU or specified by POSIX.  @xref{tzset}.
 @end itemize
 
 A more flexible function is @code{strftime}.  However, note that it is
diff --git a/doc/posix-functions/daylight.texi 
b/doc/posix-functions/daylight.texi
index d5d7a5c..4f40543 100644
--- a/doc/posix-functions/daylight.texi
+++ b/doc/posix-functions/daylight.texi
@@ -18,4 +18,10 @@ Mac OS X 10.3, FreeBSD 6.0, OpenBSD 3.8, IRIX 6.5, OSF/1 5.1.
 @item
 The address of this variable is not a compile-time constant on some platforms:
 Cygwin, mingw.
address@hidden
+Native Windows platforms (mingw, MSVC) support only a subset of time
+zones supported by GNU or specified by POSIX.  @xref{tzset}.
 @end itemize
+
+A more portable way of getting the UTC offset is to use
address@hidden with the @code{%z} format.  @xref{strftime}.
diff --git a/doc/posix-functions/localtime.texi 
b/doc/posix-functions/localtime.texi
index 74d4a6a..02d069c 100644
--- a/doc/posix-functions/localtime.texi
+++ b/doc/posix-functions/localtime.texi
@@ -19,4 +19,7 @@ Portability problems not fixed by Gnulib:
 On some platforms, this function returns nonsense values for
 unsupported arguments (like @math{2^56}), rather than failing:
 FreeBSD 10.
address@hidden
+Native Windows platforms (mingw, MSVC) support only a subset of time
+zones supported by GNU or specified by POSIX.  @xref{tzset}.
 @end itemize
diff --git a/doc/posix-functions/mktime.texi b/doc/posix-functions/mktime.texi
index 35a9a41..6187dc7 100644
--- a/doc/posix-functions/mktime.texi
+++ b/doc/posix-functions/mktime.texi
@@ -19,4 +19,7 @@ when the environment variable @code{TZ} has been set by 
Cygwin.
 
 Portability problems not fixed by Gnulib:
 @itemize
address@hidden
+Native Windows platforms (mingw, MSVC) support only a subset of time
+zones supported by GNU or specified by POSIX.  @xref{tzset}.
 @end itemize
diff --git a/doc/posix-functions/strftime.texi 
b/doc/posix-functions/strftime.texi
index 0c2d992..dd52720 100644
--- a/doc/posix-functions/strftime.texi
+++ b/doc/posix-functions/strftime.texi
@@ -19,6 +19,9 @@ Portability problems not fixed by Gnulib:
 The Windows C runtime library (which is used by MinGW) does not
 support the %e specifier (and possibly the other more recent SUS
 specifiers too, i.e., %C, %D, %h, %n, %r, %R, %t, and %T).
address@hidden
+Native Windows platforms (mingw, MSVC) support only a subset of time
+zones supported by GNU or specified by POSIX.  @xref{tzset}.
 @end itemize
 
 Extension: Gnulib offers a module @samp{strftime} that provides an
diff --git a/doc/posix-functions/timezone.texi 
b/doc/posix-functions/timezone.texi
index dfadb35..fa1ae7e 100644
--- a/doc/posix-functions/timezone.texi
+++ b/doc/posix-functions/timezone.texi
@@ -18,4 +18,10 @@ IRIX 6.5, OSF/1 5.1, mingw.
 @item
 The address of this variable is not a compile-time constant on some platforms:
 mingw.
address@hidden
+Native Windows platforms (mingw, MSVC) support only a subset of time
+zones supported by GNU or specified by POSIX.  @xref{tzset}.
 @end itemize
+
+A more portable way of getting the UTC offset is to use
address@hidden with the @code{%z} format.  @xref{strftime}.
diff --git a/doc/posix-functions/tzname.texi b/doc/posix-functions/tzname.texi
index d28cef0..8441529 100644
--- a/doc/posix-functions/tzname.texi
+++ b/doc/posix-functions/tzname.texi
@@ -18,4 +18,10 @@ IRIX 6.5, OSF/1 5.1, mingw.
 @item
 The address of this variable is not a compile-time constant on some platforms:
 Cygwin, mingw.
address@hidden
+Native Windows platforms (mingw, MSVC) support only a subset of time
+zones supported by GNU or specified by POSIX.  @xref{tzset}.
 @end itemize
+
+A more portable way of getting the time zone abbreviation is to use
address@hidden with the @code{%Z} format.  @xref{strftime}.
diff --git a/doc/posix-functions/tzset.texi b/doc/posix-functions/tzset.texi
index a457409..2e16cb4 100644
--- a/doc/posix-functions/tzset.texi
+++ b/doc/posix-functions/tzset.texi
@@ -19,4 +19,13 @@ Solaris 2.6.
 
 Portability problems not fixed by Gnulib:
 @itemize
address@hidden
+Native Windows platforms (mingw, MSVC) support only a subset of
+POSIX-specified values for the @env{TZ} environment variable,
+consisting of a time zone abbreviation containing exactly three ASCII
+letters with no daylight saving time or angle brackets, and with no
+support for @code{tz} database settings like
address@hidden'America/New_York'}.  Even this subset does not work on
+applications built via the Universal Windows Platform, as it does not
+make environment variables like @env{TZ} available to applications.
 @end itemize
diff --git a/doc/posix-functions/wcsftime.texi 
b/doc/posix-functions/wcsftime.texi
index 931b81c..0e4a951 100644
--- a/doc/posix-functions/wcsftime.texi
+++ b/doc/posix-functions/wcsftime.texi
@@ -21,4 +21,7 @@ OpenBSD 3.8, Minix 3.1.8, IRIX 5.3, Solaris 2.5.1, Cygwin 
1.5.x, BeOS.
 @item
 On AIX and Windows platforms, @code{wchar_t} is a 16-bit type and therefore 
cannot
 accommodate all Unicode characters.
address@hidden
+Native Windows platforms (mingw, MSVC) support only a subset of time
+zones specified by POSIX.  @xref{tzset}.
 @end itemize
-- 
2.9.3