[apple/libc.git] / stdtime / FreeBSD / ctime.3

.\" Copyright (c) 1989, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Arthur Olson.
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     From: @(#)ctime.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/stdtime/ctime.3,v 1.22 2004/07/02 23:52:12 ru Exp $
.\"
.Dd January 2, 1999
.Dt CTIME 3
.Os
.Sh NAME
.Nm asctime ,
.Nm asctime_r ,
.Nm ctime ,
.Nm ctime_r ,
.Nm difftime ,
.Nm gmtime ,
.Nm gmtime_r ,
.Nm localtime ,
.Nm localtime_r ,
.Nm mktime ,
.Nm timegm
.Nd transform binary date and time values
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In time.h
.Vt extern char *tzname[2] ;
.Ft char *
.Fn ctime "const time_t *clock"
.Ft double
.Fn difftime "time_t time1" "time_t time0"
.Ft char *
.Fn asctime "const struct tm *tm"
.Ft struct tm *
.Fn localtime "const time_t *clock"
.Ft struct tm *
.Fn gmtime "const time_t *clock"
.Ft time_t
.Fn mktime "struct tm *tm"
.Ft time_t
.Fn timegm "struct tm *tm"
.Ft char *
.Fn ctime_r "const time_t *clock" "char *buf"
.Ft struct tm *
.Fn localtime_r "const time_t *clock" "struct tm *result"
.Ft struct tm *
.Fn gmtime_r "const time_t *clock" "struct tm *result"
.Ft char *
.Fn asctime_r "const struct tm *tm" "char *buf"
.Sh DESCRIPTION
The functions
.Fn ctime ,
.Fn gmtime
and
.Fn localtime
all take as an argument a time value representing the time in seconds since
the Epoch (00:00:00
.Tn UTC ,
January 1, 1970; see
.Xr time 3 ) .
.Pp
The function
.Fn localtime
converts the time value pointed at by
.Fa clock ,
and returns a pointer to a
.Dq Fa struct tm
(described below) which contains
the broken-out time information for the value after adjusting for the current
time zone (and any other factors such as Daylight Saving Time).
Time zone adjustments are performed as specified by the
.Ev TZ
environment variable (see
.Xr tzset 3 ) .
The function
.Fn localtime
uses
.Xr tzset 3
to initialize time conversion information if
.Xr tzset 3
has not already been called by the process.
.Pp
After filling in the tm structure,
.Fn localtime
sets the
.Fa tm_isdst Ns 'th
element of
.Fa tzname
to a pointer to an
.Tn ASCII
string that's the time zone abbreviation to be
used with
.Fn localtime Ns 's
return value.
.Pp
The function
.Fn gmtime
similarly converts the time value, but without any time zone adjustment,
and returns a pointer to a tm structure (described below).
.Pp
The
.Fn ctime
function
adjusts the time value for the current time zone in the same manner as
.Fn localtime ,
and returns a pointer to a 26-character string of the form:
.Bd -literal -offset indent
Thu Nov 24 18:22:48 1986\en\e0
.Ed
.Pp
All the fields have constant width.
.Pp
The
.Fn ctime_r
function
provides the same functionality as
.Fn ctime
except the caller must provide the output buffer
.Fa buf
to store the result, which must be at least 26 characters long.
The
.Fn localtime_r
and
.Fn gmtime_r
functions
provide the same functionality as
.Fn localtime
and
.Fn gmtime
respectively, except the caller must provide the output buffer
.Fa result .
.Pp
The
.Fn asctime
function
converts the broken down time in the structure
.Fa tm
pointed at by
.Fa *tm
to the form
shown in the example above.
.Pp
The
.Fn asctime_r
function
provides the same functionality as
.Fn asctime
except the caller provide the output buffer
.Fa buf
to store the result, which must be at least 26 characters long.
.Pp
The functions
.Fn mktime
and
.Fn timegm
convert the broken-down time in the structure
pointed to by tm into a time value with the same encoding as that of the
values returned by the
.Xr time 3
function (that is, seconds from the Epoch,
.Tn UTC ) .
The
.Fn mktime
function
interprets the input structure according to the current timezone setting
(see
.Xr tzset 3 ) .
The
.Fn timegm
function
interprets the input structure as representing Universal Coordinated Time
.Pq Tn UTC .
.Pp
The original values of the
.Fa tm_wday
and
.Fa tm_yday
components of the structure are ignored, and the original values of the
other components are not restricted to their normal ranges, and will be
normalized if needed.
For example,
October 40 is changed into November 9,
a
.Fa tm_hour
of \-1 means 1 hour before midnight,
.Fa tm_mday
of 0 means the day preceding the current month, and
.Fa tm_mon
of \-2 means 2 months before January of
.Fa tm_year .
(A positive or zero value for
.Fa tm_isdst
causes
.Fn mktime
to presume initially that summer time (for example, Daylight Saving Time)
is or is not in effect for the specified time, respectively.
A negative value for
.Fa tm_isdst
causes the
.Fn mktime
function to attempt to divine whether summer time is in effect for the
specified time.
The
.Fa tm_isdst
and
.Fa tm_gmtoff
members are forced to zero by
.Fn timegm . )
.Pp
On successful completion, the values of the
.Fa tm_wday
and
.Fa tm_yday
components of the structure are set appropriately, and the other components
are set to represent the specified calendar time, but with their values
forced to their normal ranges; the final value of
.Fa tm_mday
is not set until
.Fa tm_mon
and
.Fa tm_year
are determined.
The
.Fn mktime
function
returns the specified calendar time; if the calendar time cannot be
represented, it returns \-1;
.Pp
The
.Fn difftime
function
returns the difference between two calendar times,
.Pf ( Fa time1
-
.Fa time0 ) ,
expressed in seconds.
.Pp
External declarations as well as the tm structure definition are in the
.In time.h
include file.
The tm structure includes at least the following fields:
.Bd -literal -offset indent
int tm_sec;	/\(** seconds (0 - 60) \(**/
int tm_min;	/\(** minutes (0 - 59) \(**/
int tm_hour;	/\(** hours (0 - 23) \(**/
int tm_mday;	/\(** day of month (1 - 31) \(**/
int tm_mon;	/\(** month of year (0 - 11) \(**/
int tm_year;	/\(** year \- 1900 \(**/
int tm_wday;	/\(** day of week (Sunday = 0) \(**/
int tm_yday;	/\(** day of year (0 - 365) \(**/
int tm_isdst;	/\(** is summer time in effect? \(**/
char \(**tm_zone;	/\(** abbreviation of timezone name \(**/
long tm_gmtoff;	/\(** offset from UTC in seconds \(**/
.Ed
.Pp
The
field
.Fa tm_isdst
is non-zero if summer time is in effect.
.Pp
The field
.Fa tm_gmtoff
is the offset (in seconds) of the time represented from
.Tn UTC ,
with positive
values indicating east of the Prime Meridian.
.Sh SEE ALSO
.Xr date 1 ,
.Xr gettimeofday 2 ,
.Xr getenv 3 ,
.Xr time 3 ,
.Xr tzset 3 ,
.Xr tzfile 5
.Sh STANDARDS
The
.Fn asctime ,
.Fn ctime ,
.Fn difftime ,
.Fn gmtime ,
.Fn localtime ,
and
.Fn mktime
functions conform to
.St -isoC ,
and conform to
.St -p1003.1-96
provided the selected local timezone does not contain a leap-second table
(see
.Xr zic 8 ) .
.Pp
The
.Fn asctime_r ,
.Fn ctime_r ,
.Fn gmtime_r ,
and
.Fn localtime_r
functions are expected to conform to
.St -p1003.1-96
(again provided the selected local timezone does not contain a leap-second
table).
.Pp
The
.Fn timegm
function is not specified by any standard; its function cannot be
completely emulated using the standard functions described above.
.Sh HISTORY
This manual page is derived from
the time package contributed to Berkeley by
.An Arthur Olson
and which appeared in
.Bx 4.3 .
.Sh BUGS
Except for
.Fn difftime ,
.Fn mktime ,
and the
.Fn \&_r
variants of the other functions,
these functions leaves their result in an internal static object and return
a pointer to that object.
Subsequent calls to these
function will modify the same object.
.Pp
The C Standard provides no mechanism for a program to modify its current
local timezone setting, and the
.Tn POSIX Ns No \&-standard
method is not reentrant.
(However, thread-safe implementations are provided
in the
.Tn POSIX
threaded environment.)
.Pp
The
.Va tm_zone
field of a returned
.Vt tm
structure points to a static array of characters,
which will also be overwritten by any subsequent calls (as well as by
subsequent calls to
.Xr tzset 3
and
.Xr tzsetwall 3 ) .
.Pp
Use of the external variable
.Fa tzname
is discouraged; the
.Fa tm_zone
entry in the tm structure is preferred.
Commit	Line	Data
5b2abdfb A	1	.\" Copyright (c) 1989, 1991, 1993
	2	.\" The Regents of the University of California. All rights reserved.
	3	.\"
	4	.\" This code is derived from software contributed to Berkeley by
	5	.\" Arthur Olson.
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\" 3. All advertising materials mentioning features or use of this software
	15	.\" must display the following acknowledgement:
	16	.\" This product includes software developed by the University of
	17	.\" California, Berkeley and its contributors.
	18	.\" 4. Neither the name of the University nor the names of its contributors
	19	.\" may be used to endorse or promote products derived from this software
	20	.\" without specific prior written permission.
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	23	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	24	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	25	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	26	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	27	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	28	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	29	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	30	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	31	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	32	.\" SUCH DAMAGE.
	33	.\"
	34	.\" From: @(#)ctime.3 8.1 (Berkeley) 6/4/93
3d9156a7	35	.\" $FreeBSD: src/lib/libc/stdtime/ctime.3,v 1.22 2004/07/02 23:52:12 ru Exp $
5b2abdfb A	36	.\"
	37	.Dd January 2, 1999
	38	.Dt CTIME 3
	39	.Os
	40	.Sh NAME
	41	.Nm asctime ,
	42	.Nm asctime_r ,
	43	.Nm ctime ,
	44	.Nm ctime_r ,
	45	.Nm difftime ,
	46	.Nm gmtime ,
	47	.Nm gmtime_r ,
	48	.Nm localtime ,
	49	.Nm localtime_r ,
	50	.Nm mktime ,
	51	.Nm timegm
	52	.Nd transform binary date and time values
	53	.Sh LIBRARY
	54	.Lb libc
	55	.Sh SYNOPSIS
	56	.In time.h
	57	.Vt extern char *tzname[2] ;
	58	.Ft char *
	59	.Fn ctime "const time_t *clock"
	60	.Ft double
	61	.Fn difftime "time_t time1" "time_t time0"
	62	.Ft char *
	63	.Fn asctime "const struct tm *tm"
	64	.Ft struct tm *
	65	.Fn localtime "const time_t *clock"
	66	.Ft struct tm *
	67	.Fn gmtime "const time_t *clock"
	68	.Ft time_t
	69	.Fn mktime "struct tm *tm"
	70	.Ft time_t
	71	.Fn timegm "struct tm *tm"
	72	.Ft char *
	73	.Fn ctime_r "const time_t clock" "char buf"
	74	.Ft struct tm *
	75	.Fn localtime_r "const time_t clock" "struct tm result"
	76	.Ft struct tm *
	77	.Fn gmtime_r "const time_t clock" "struct tm result"
	78	.Ft char *
	79	.Fn asctime_r "const struct tm tm" "char buf"
	80	.Sh DESCRIPTION
	81	The functions
	82	.Fn ctime ,
	83	.Fn gmtime
	84	and
	85	.Fn localtime
	86	all take as an argument a time value representing the time in seconds since
	87	the Epoch (00:00:00
	88	.Tn UTC ,
	89	January 1, 1970; see
	90	.Xr time 3 ) .
	91	.Pp
	92	The function
	93	.Fn localtime
	94	converts the time value pointed at by
	95	.Fa clock ,
	96	and returns a pointer to a
	97	.Dq Fa struct tm
	98	(described below) which contains
	99	the broken-out time information for the value after adjusting for the current
100	time zone (and any other factors such as Daylight Saving Time).
101	Time zone adjustments are performed as specified by the
102	.Ev TZ
103	environment variable (see
104	.Xr tzset 3 ) .
105	The function
106	.Fn localtime
107	uses
108	.Xr tzset 3
109	to initialize time conversion information if
110	.Xr tzset 3
111	has not already been called by the process.
112	.Pp
113	After filling in the tm structure,
114	.Fn localtime
115	sets the
116	.Fa tm_isdst Ns 'th
117	element of
118	.Fa tzname
119	to a pointer to an
120	.Tn ASCII
121	string that's the time zone abbreviation to be
122	used with
123	.Fn localtime Ns 's
124	return value.
125	.Pp
126	The function
127	.Fn gmtime
128	similarly converts the time value, but without any time zone adjustment,
129	and returns a pointer to a tm structure (described below).
130	.Pp
131	The
132	.Fn ctime
133	function
134	adjusts the time value for the current time zone in the same manner as
135	.Fn localtime ,
136	and returns a pointer to a 26-character string of the form:
137	.Bd -literal -offset indent
138	Thu Nov 24 18:22:48 1986\en\e0
139	.Ed
140	.Pp
141	All the fields have constant width.
142	.Pp
9385eb3d	143	The
5b2abdfb	144	.Fn ctime_r
9385eb3d	145	function
5b2abdfb A	146	provides the same functionality as
	147	.Fn ctime
	148	except the caller must provide the output buffer
	149	.Fa buf
	150	to store the result, which must be at least 26 characters long.
9385eb3d	151	The
5b2abdfb A	152	.Fn localtime_r
	153	and
	154	.Fn gmtime_r
9385eb3d	155	functions
5b2abdfb A	156	provide the same functionality as
	157	.Fn localtime
	158	and
	159	.Fn gmtime
	160	respectively, except the caller must provide the output buffer
	161	.Fa result .
	162	.Pp
	163	The
	164	.Fn asctime
	165	function
	166	converts the broken down time in the structure
	167	.Fa tm
	168	pointed at by
	169	.Fa *tm
	170	to the form
	171	shown in the example above.
	172	.Pp
9385eb3d	173	The
5b2abdfb	174	.Fn asctime_r
9385eb3d	175	function
5b2abdfb A	176	provides the same functionality as
	177	.Fn asctime
	178	except the caller provide the output buffer
	179	.Fa buf
	180	to store the result, which must be at least 26 characters long.
	181	.Pp
	182	The functions
	183	.Fn mktime
	184	and
	185	.Fn timegm
	186	convert the broken-down time in the structure
	187	pointed to by tm into a time value with the same encoding as that of the
	188	values returned by the
	189	.Xr time 3
	190	function (that is, seconds from the Epoch,
	191	.Tn UTC ) .
9385eb3d	192	The
5b2abdfb	193	.Fn mktime
9385eb3d	194	function
5b2abdfb A	195	interprets the input structure according to the current timezone setting
	196	(see
	197	.Xr tzset 3 ) .
9385eb3d	198	The
5b2abdfb	199	.Fn timegm
9385eb3d	200	function
5b2abdfb A	201	interprets the input structure as representing Universal Coordinated Time
	202	.Pq Tn UTC .
	203	.Pp
	204	The original values of the
	205	.Fa tm_wday
	206	and
	207	.Fa tm_yday
	208	components of the structure are ignored, and the original values of the
	209	other components are not restricted to their normal ranges, and will be
	210	normalized if needed.
	211	For example,
	212	October 40 is changed into November 9,
	213	a
	214	.Fa tm_hour
	215	of \-1 means 1 hour before midnight,
	216	.Fa tm_mday
	217	of 0 means the day preceding the current month, and
	218	.Fa tm_mon
	219	of \-2 means 2 months before January of
	220	.Fa tm_year .
	221	(A positive or zero value for
	222	.Fa tm_isdst
	223	causes
	224	.Fn mktime
	225	to presume initially that summer time (for example, Daylight Saving Time)
	226	is or is not in effect for the specified time, respectively.
	227	A negative value for
	228	.Fa tm_isdst
	229	causes the
	230	.Fn mktime
	231	function to attempt to divine whether summer time is in effect for the
	232	specified time.
	233	The
	234	.Fa tm_isdst
	235	and
	236	.Fa tm_gmtoff
	237	members are forced to zero by
	238	.Fn timegm . )
	239	.Pp
	240	On successful completion, the values of the
	241	.Fa tm_wday
	242	and
	243	.Fa tm_yday
	244	components of the structure are set appropriately, and the other components
	245	are set to represent the specified calendar time, but with their values
	246	forced to their normal ranges; the final value of
	247	.Fa tm_mday
	248	is not set until
	249	.Fa tm_mon
	250	and
	251	.Fa tm_year
	252	are determined.
9385eb3d A	253	The
	254	.Fn mktime
	255	function
5b2abdfb A	256	returns the specified calendar time; if the calendar time cannot be
	257	represented, it returns \-1;
	258	.Pp
	259	The
	260	.Fn difftime
	261	function
	262	returns the difference between two calendar times,
	263	.Pf ( Fa time1
	264	-
	265	.Fa time0 ) ,
	266	expressed in seconds.
	267	.Pp
	268	External declarations as well as the tm structure definition are in the
3d9156a7	269	.In time.h
5b2abdfb A	270	include file.
	271	The tm structure includes at least the following fields:
	272	.Bd -literal -offset indent
	273	int tm_sec; /\( seconds (0 - 60) \(/
	274	int tm_min; /\( minutes (0 - 59) \(/
	275	int tm_hour; /\( hours (0 - 23) \(/
	276	int tm_mday; /\( day of month (1 - 31) \(/
	277	int tm_mon; /\( month of year (0 - 11) \(/
	278	int tm_year; /\( year \- 1900 \(/
	279	int tm_wday; /\( day of week (Sunday = 0) \(/
	280	int tm_yday; /\( day of year (0 - 365) \(/
	281	int tm_isdst; /\( is summer time in effect? \(/
	282	char \(tm_zone; /\( abbreviation of timezone name \(**/
	283	long tm_gmtoff; /\( offset from UTC in seconds \(/
	284	.Ed
	285	.Pp
	286	The
	287	field
	288	.Fa tm_isdst
	289	is non-zero if summer time is in effect.
	290	.Pp
	291	The field
	292	.Fa tm_gmtoff
	293	is the offset (in seconds) of the time represented from
	294	.Tn UTC ,
	295	with positive
	296	values indicating east of the Prime Meridian.
	297	.Sh SEE ALSO
	298	.Xr date 1 ,
	299	.Xr gettimeofday 2 ,
	300	.Xr getenv 3 ,
	301	.Xr time 3 ,
	302	.Xr tzset 3 ,
	303	.Xr tzfile 5
	304	.Sh STANDARDS
	305	The
	306	.Fn asctime ,
	307	.Fn ctime ,
	308	.Fn difftime ,
	309	.Fn gmtime ,
	310	.Fn localtime ,
	311	and
	312	.Fn mktime
	313	functions conform to
	314	.St -isoC ,
	315	and conform to
	316	.St -p1003.1-96
	317	provided the selected local timezone does not contain a leap-second table
	318	(see
	319	.Xr zic 8 ) .
	320	.Pp
	321	The
	322	.Fn asctime_r ,
	323	.Fn ctime_r ,
	324	.Fn gmtime_r ,
	325	and
	326	.Fn localtime_r
	327	functions are expected to conform to
	328	.St -p1003.1-96
	329	(again provided the selected local timezone does not contain a leap-second
	330	table).
	331	.Pp
	332	The
	333	.Fn timegm
334	function is not specified by any standard; its function cannot be
335	completely emulated using the standard functions described above.
336	.Sh HISTORY
337	This manual page is derived from
338	the time package contributed to Berkeley by
339	.An Arthur Olson
340	and which appeared in
341	.Bx 4.3 .
342	.Sh BUGS
343	Except for
344	.Fn difftime ,
345	.Fn mktime ,
346	and the
347	.Fn \&_r
348	variants of the other functions,
349	these functions leaves their result in an internal static object and return
350	a pointer to that object.
351	Subsequent calls to these
352	function will modify the same object.
353	.Pp
354	The C Standard provides no mechanism for a program to modify its current
355	local timezone setting, and the
356	.Tn POSIX Ns No \&-standard
3d9156a7 A	357	method is not reentrant.
3d9156a7 A	358	(However, thread-safe implementations are provided
5b2abdfb A	359	in the
	360	.Tn POSIX
	361	threaded environment.)
	362	.Pp
	363	The
9385eb3d A	364	.Va tm_zone
	365	field of a returned
	366	.Vt tm
	367	structure points to a static array of characters,
5b2abdfb A	368	which will also be overwritten by any subsequent calls (as well as by
	369	subsequent calls to
	370	.Xr tzset 3
	371	and
	372	.Xr tzsetwall 3 ) .
	373	.Pp
	374	Use of the external variable
	375	.Fa tzname
	376	is discouraged; the
	377	.Fa tm_zone
	378	entry in the tm structure is preferred.