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From: karl@ima.isc.com (Karl Heuer)
Newsgroups: comp.std.c
Subject: Re: Questions about mktime() - and answer
Message-ID: <1991Feb14.032409.27062@dirtydog.ima.isc.com>
Date: 14 Feb 91 03:24:09 GMT
References: <1991Feb8.062954.13509@druid.uucp>
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Reply-To: karl@ima.isc.com (Karl Heuer)
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In article <1991Feb8.062954.13509@druid.uucp> darcy@druid.uucp (D'Arcy J.M. Cain) writes:
>time_t	mktime(struct tm *tp) { ...
>    *tp = *localtime(&t);		/* set other fields in structure */
>    return(t);
>}

Sorry, this violates the Standard.  "The implementation shall behave as if
no other library function calls [localtime()]." [4.12.3].  In particular,
the user has the right to assume that the static structure maintained by
localtime() is not destroyed by a call to mktime().

Fix: move the guts of localtime() into void _do_time(time_t, struct tm *),
reimplement localtime(time_t *pt) as _do_time(*pt, &statictm), and change
"*tp = *localtime(&t);" in mktime() to "_do_time(t, tp)".

Karl W. Z. Heuer (karl@ima.isc.com or uunet!ima!karl), The Walking Lint