> On Jul 20, 2026, at 7:57 PM, Paul Gilmartin via tz <[email protected]> wrote:
>
> On 7/20/26 16:20, Steffen Nurpmeso wrote:
>> Paul Eggert via tz wrote in
>> ...
>> |tzcode provides a way: if tzalloc("ABC") returns a null pointer and
>> |errno has a value other than ENOMEM, then "ABC" is invalid. So if you're
>> |on platforms like NetBSD that have tzalloc, you have a way. Or you can
>> |copy tzcode and use its tzalloc.
>>
> This appears to be a thread-safe replacement
> for localtime(). I need to RTFM more.
localtime_r() already serves as a thread-safe replacement for localtime() in
most cases.
However:
> o localtime() should have a time_t argument.
localtime() does have a time_t argument, and the time argument to localtime_r()
is also a time_t.
The same applies to the time argument to localtime_rz()
(https://man.netbsd.org/localtime_rz.3).
> I see no such for tzalloc().
This is for the case where localtime_r() is *not* sufficient as a thread-safe
replacement for localtime()...
...i.e., the case where different threads want to convert a time_t to local
time in some *arbitrary* timezone, with the timezone being thread-specific.
Tweaking the TZ environment variable (if possible, e.g. using setenv()) isn't
thread-safe.
> o strftime() needs a struct tm argument. Does tzalloc() generate one?
No.
tzalloc(), as Paul Eggert noted, takes a string argument containing a tzid and
return s pointer to an object that represents the timezone corresponding to
that tzid. It can be used in localtime_rz() calls to convert a time_t value to
a struct tm value for the local time that the time_t represents in that
timezone, passed to ctime_rz() to convert a time_t value to a string for the
local time that the time_t represents in that timezone, and to mltime_z() to
convert a struct tm to the time_t that it represents in that timezone.
tzfree() frees the object in question.
