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From: Corinna Vinschen <corinna@sourceware.org> To: cygwin-cvs@sourceware.org Subject: [newlib-cygwin] winsup/doc/faq-api.xml(faq.api.timezone): explain time zone updates Date: Thu, 27 Aug 2020 08:54:21 +0000 (GMT) [thread overview] Message-ID: <20200827085421.CFBFB386F419@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=573dda0cf2efa947a9c3d665abc1d94a0d600a9e commit 573dda0cf2efa947a9c3d665abc1d94a0d600a9e Author: Brian Inglis <Brian.Inglis@SystematicSW.ab.ca> Date: Thu Aug 27 01:17:09 2020 -0600 winsup/doc/faq-api.xml(faq.api.timezone): explain time zone updates based on material from tz@IANA.org mailing list sources Diff: --- winsup/doc/faq-api.xml | 40 +++++++++++++++++++++++++++++++++++----- 1 file changed, 35 insertions(+), 5 deletions(-) diff --git a/winsup/doc/faq-api.xml b/winsup/doc/faq-api.xml index 829e4d7fe..6283fb663 100644 --- a/winsup/doc/faq-api.xml +++ b/winsup/doc/faq-api.xml @@ -385,13 +385,43 @@ Cygwin version number details, check out the </answer></qandaentry> <qandaentry id="faq.api.timezone"> -<question><para>Why isn't timezone set correctly?</para></question> +<question><para>Why isn't my time (or zone) set correctly?</para></question> <answer> -<para><emphasis role='bold'>(Please note: This section has not yet been updated for the latest net release.)</emphasis> -</para> -<para>Did you explicitly call tzset() before checking the value of timezone? -If not, you must do so. +<para>Daylight saving (Summer time) and other time zone changes are +decided on by politicians, and announced by government officials, +sometimes with short or no notice, so time zone updates are released at +least a few, and sometimes several, times a year. +Details of changes are not known until they are announced publicly by +officials, often in foreign languages. +Those details then have to be noticed, possibly translated, passed to, +picked up, and applied by the official <filename>tzdata</filename> +source package maintainers. +That information has to be compiled, checked, and released publicly in +an update to the official <filename>tzdata</filename> source package. +Then those changes have to be picked up and applied to the Cygwin +<filename>tzdata</filename> package, which has to be updated, built, +tested, and released publicly. +</para> +<para>Time zone settings are updates to the daylight saving (Summer +time) rules for dates of changes, hour offsets from UTC of time zones, +and the geographic regions to which those rules and offsets apply, +provided in the <filename>tzdata</filename> package included in all +Cygwin installations. +Have you run the Cygwin Setup program recently to update at least +the <filename>tzdata</filename> package? +</para> +<para>Are you developing applications using times which may be affected +by time zones? +Since the <literal>ctime()</literal>, <literal>localtime()</literal>, +<literal>mktime()</literal>, and <literal>strftime()</literal> functions +are required to set time zone information as if by calling +<literal>tzset()</literal>, there is no need for an explicit +<literal>tzset()</literal> call before using these functions. +However, if none of the above functions are called first, applications +should ensure <literal>tzset()</literal> is called explicitly before +using any other time functions, or checking or using time zone +information. </para> </answer></qandaentry>
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