Re: strftime(3) oddities with %s, %z

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> Making the output of %s be implementation defined or unspecified
> would be the same as the situation we're in now (where %s isn't in
> the current standard at all) and so, what it produces if used is
> simply unspecified.

But it would be documented as doing what it actually does, instead of
being documented as printing a value that isn't there and can, at best,
be only guessed at.

If %s were documented as printing the number that would be obtained by
calling mktime() on the struct tm?  That would (a) be telling the
actual truth, (b) would match existing implementations, and (c) would
not mislead people into thinking it did something it doesn't (and,
without ABI and possibly API changes, can't).

I think the best change here is to bite the bullet and accept that the
current interface, entrenched as it may be, is broken, either changing
strftime and struct tm incompatibly or creating new strftime- and
struct tm-alikes and abandoning strftime and struct tm to the same
legacy status as the second arg to gettimeofday().

I think the best _likely_ change is to fix what %s is defined to print,
and, preferably, do likewise for any other format specifiers which are
similarly mis-described.

>> No, there is no obligation to standardize incorrect behavior.
> Of course not.  But there is nothing incorrect here.

I too think there is.  At the barest minimum, the documentation is
incorrect (it speaks of printing a number that isn't in the input
struct and, as evidenced in this thread, can't be reliably obtained
from that struct without undocumented assumptions).

The design is broken.  The right thing to do is to fix it, either with
a flag day or by freezing the broken design, keeping it only for
backward compatability, and creating a less-broken replacement.  The
latter has happened often enough before.  (Examples are
sigpause->sigsuspend or select->poll; the examples that come to mind
are syscalls because they're what I use most.  I have a fuzzy memory
that there's one that has been through that twice, but I can't recall
it now.)

>> For my part, I had never had any idea you couldn't use strftime with
>> gmtime() results, [...]
> You can, mostly.

Where is it documented what works and what doesn't?  Those reading this
thread now know that %s doesn't work in that case, but this thread
hardly counts as documentation.  What else doesn't work?  Where is all
that - heck, any of that - specified and documented?

Until and unless it is, I maintain that dholland is right: you can't
(reliably) use strftime with gmtime() - or anything else not returned
directly from localtime() - because you're playing implementation
roulette with whether the formats you think you want will do what you
actually want.

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