Differential D39712 Diff 121070 contrib/tzcode/newctime.3

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contrib/tzcode/newctime.3

	.\" This file is in the public domain, so clarified as of			.\" This file is in the public domain, so clarified as of
	.\" 2009-05-17 by Arthur David Olson.			.\" 2009-05-17 by Arthur David Olson.
	.TH NEWCTIME 3			.TH newctime 3 "" "Time Zone Database"
	.SH NAME			.SH NAME
	asctime, ctime, difftime, gmtime, localtime, mktime \- convert date and time			asctime, ctime, difftime, gmtime, localtime, mktime \- convert date and time
	.SH SYNOPSIS			.SH SYNOPSIS
	.nf			.nf
	.ie \n(.g .ds - \f(CR-\fP			.ie \n(.g .ds - \f(CR-\fP
	.el .ds - \-			.el .ds - \-
	.B #include <time.h>			.B #include <time.h>
	.PP			.PP
	.BR "extern char tzname[];" " /\(* (optional) \(**/"			.BR "extern char tzname[];" " /\(* (optional) \(**/"
	.PP			.PP
	.B char ctime(time_t const clock);			.B [[deprecated]] char ctime(time_t const clock);
	.PP			.PP
	.B char ctime_r(time_t const clock, char *buf);			.B char ctime_r(time_t const clock, char *buf);
	.PP			.PP
	.B double difftime(time_t time1, time_t time0);			.B double difftime(time_t time1, time_t time0);
	.PP			.PP
	.B char asctime(struct tm const tm);			.B [[deprecated]] char asctime(struct tm const tm);
	.PP			.PP
	.B "char asctime_r(struct tm const restrict tm,"			.B "char asctime_r(struct tm const restrict tm,"
	.B " char *restrict result);"			.B " char *restrict result);"
	.PP			.PP
	.B struct tm localtime(time_t const clock);			.B struct tm localtime(time_t const clock);
	.PP			.PP
	.B "struct tm localtime_r(time_t const restrict clock,"			.B "struct tm localtime_r(time_t const restrict clock,"
	.B " struct tm *restrict result);"			.B " struct tm *restrict result);"
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	The POSIX standard says that timestamps must be nonnegative			The POSIX standard says that timestamps must be nonnegative
	and must ignore leap seconds.			and must ignore leap seconds.
	Many implementations extend POSIX by allowing negative timestamps,			Many implementations extend POSIX by allowing negative timestamps,
	and can therefore represent timestamps that predate the			and can therefore represent timestamps that predate the
	introduction of UTC and are some other flavor of Universal Time (UT).			introduction of UTC and are some other flavor of Universal Time (UT).
	Some implementations support leap seconds, in contradiction to POSIX.			Some implementations support leap seconds, in contradiction to POSIX.
	.PP			.PP
	The			The
				.B ctime
				function is deprecated starting in C23.
				Callers can use
				.B localtime_r
				and
				.B strftime
				instead.
				.PP
				The
	.B localtime			.B localtime
	and			and
	.B gmtime			.B gmtime
	functions			functions
	return pointers to			return pointers to
	.q "tm"			.q "tm"
	structures, described below.			structures, described below.
	The			The
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	The			The
	.B asctime			.B asctime
	function			function
	converts a time value contained in a			converts a time value contained in a
	.q "tm"			.q "tm"
	structure to a string,			structure to a string,
	as shown in the above example,			as shown in the above example,
	and returns a pointer to the string.			and returns a pointer to the string.
				This function is deprecated starting in C23.
				Callers can use
				.B strftime
				instead.
	.PP			.PP
	The			The
	.B mktime			.B mktime
	function			function
	converts the broken-down time,			converts the broken-down time,
	expressed as local time,			expressed as local time,
	in the structure pointed to by			in the structure pointed to by
	.I tm			.I tm
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	will			will
	continue to exist in this form in future releases of this code.			continue to exist in this form in future releases of this code.
	.SH FILES			.SH FILES
	.ta \w'/usr/share/zoneinfo/posixrules\0\0'u			.ta \w'/usr/share/zoneinfo/posixrules\0\0'u
	/usr/share/zoneinfo timezone information directory			/usr/share/zoneinfo timezone information directory
	.br			.br
	/usr/share/zoneinfo/localtime local timezone file			/usr/share/zoneinfo/localtime local timezone file
	.br			.br
	/usr/share/zoneinfo/posixrules used with POSIX-style TZ's			/usr/share/zoneinfo/posixrules default DST rules (obsolete,
				and can cause bugs if present)
	.br			.br
	/usr/share/zoneinfo/GMT for UTC leap seconds			/usr/share/zoneinfo/GMT for UTC leap seconds
	.sp			.sp
	If			If
	.B /usr/share/zoneinfo/GMT			.B /usr/share/zoneinfo/GMT
	is absent,			is absent,
	UTC leap seconds are loaded from			UTC leap seconds are loaded from
	.BR /usr/share/zoneinfo/posixrules .			.BR /usr/share/zoneinfo/posixrules .
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