[tz] Buggy %z behaviour in strftime

Almaz Mingaleev mingaleev at google.com
Mon Jul 18 10:56:14 UTC 2022

Tried to set tm_isdst to 0 and 1. With glibc and tzcode strftime
the result is the same, they print +0000. MacOs works as
expected - it prints standard and DST offsets.
Though when I set it to -1 both glibc and MacOs just skip
%z. tzcode's implementation replaces %z with +0000 in that

On Mon, 18 Jul 2022 at 11:04, Michael H Deckers <
michael.h.deckers at googlemail.com> wrote:

> On 2022-07-18 09:34, Almaz Mingaleev via tz wrote:
> > Setting tm_gmtoff "fixes" it.
>      According to page 366 in the newest C draft standard at
> [https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2912.pdf],
>      strftime() looks at the member .tm_isdst for the format patterns
>      %z and %Z; but this member was not initialized and is therefore
>      "indeterminate", so that the result produced by strftime() may
>      be "unspecified".
>      By the way, the draft standard seems to be defective in that
>      it does not state that strftime() also looks at the members
>      .tm_year, .tm_mon, tm_mday, .tm_hour, .tm_min, .tm_sec
>      for printing %z or %Z -- one cannot determine the offset
>      or the time zone abbreviation without knowing the timestamp.
>      Michael Deckers.
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