On 10/29/2010 03:44 PM, Ken Brown wrote:
> While trying to debug a timezone problem in the Cygwin build of emacs, I've
> come across a difference between Cygwin and Linux in the behavior of
> localtime with respect to TZ. Suppose I set TZ, call localtime, unset TZ,
> and call localtime again. On Cygwin, the second call to localtime re-uses
> the previous value of TZ. On Linux, localtime reverts to giving local
> information, just as if TZ had never been set. Here's a Simple Test Case:
>
> #include <time.h>
> #include <stdio.h>
>
> extern char **environ;
>
> void
> unset_TZ (void)
> {
> char **from, **to;
> for (to = from = environ; (*to = *from); from++)
> if (! (to[0][0] == 'T' && to[0][1] == 'Z' && to[0][2] == '='))
> to++;
> }
Messing directly with environ is your problem. POSIX says that it is
only portable to traverse (but not modify) environ's contents, or to
completely assign a new array to environ. By going behind cygwin's
back, and not using unsetenv(), you have violated POSIX and can't expect
sane results.
>
> int
> main (void)
> {
> time_t now = time ((time_t *) 0);
> printf ("TZ is initially unset; hour = %d\n", localtime (&now)->tm_hour);
> putenv ("TZ=GMT0");
> printf ("TZ=GMT0; hour = %d\n", localtime (&now)->tm_hour);
> unset_TZ ();
> printf ("TZ unset; hour = %d\n", localtime (&now)->tm_hour);
> putenv ("TZ=PST8");
> printf ("TZ=PST8; hour = %d\n", localtime (&now)->tm_hour);
> unset_TZ ();
> printf ("TZ unset again; hour = %d\n", localtime (&now)->tm_hour);
> }
If properly using unsetenv("TZ") still causes problems, then we should
investigate further.
--
Eric Blake ebl...@redhat.com +1-801-349-2682
Libvirt virtualization library http://libvirt.org
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