.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved. The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\" @(#)ctime.3 6.5 (Berkeley) %G%
ctime, localtime, gmtime, asctime, timezone, tzset, tzsetwall \- convert date and time to ASCII
.B extern char *tzname[2];
.B struct tm *localtime(clock)
.B struct tm *gmtime(clock)
.B char *timezone(zone, dst)
\fITzset\fP uses the value of the environment variable \fBTZ\fP to set time
conversion information used by \fIlocaltime\fP. If \fBTZ\fP does not appear
in the environment, the best available approximation to local wall clock
time is used by \fIlocaltime\fP. If \fBTZ\fP appears in the environment
but its value is a null string, Greenwich Mean Time is used; if \fBTZ\fP
appears and begins with a slash, it is used as the absolute pathname of the
\fItzfile\fP(5)-format file from which to read the time conversion
information; if \fBTZ\fP appears and begins with a character other than a
slash, it's used as a pathname relative to a system time conversion
\fITzsetwall\fP sets things up so that \fIlocaltime\fP returns the best
available approximation of local wall clock time.
\fICtime\fP converts a long integer, pointed to by \fIclock\fP,
such as returned by \fItime\fP(2) into ASCII adn returns a pointer
to a 26-character string in the following form. All the fields
Sun Sep 16 01:03:52 1973\\n\\0
return pointers to structures containing
corrects for the time zone and possible daylight savings time;
converts directly to GMT, which is the time UNIX uses.
converts a broken-down time to ASCII and returns a pointer
to a 26-character string.
The structure declaration from the include file is:
.nr .0 .8i+\w'int tm_isdst'u
.ta .5i \n(.0u \n(.0u+\w'/* 0-000'u+1n
int tm_sec; /* 0-59 seconds */
int tm_min; /* 0-59 minutes */
int tm_hour; /* 0-23 hour */
int tm_mday; /* 1-31 day of month */
int tm_mon; /* 0-11 month */
int tm_year; /* 0- year \- 1900 */
int tm_wday; /* 0-6 day of week (Sunday = 0) */
int tm_yday; /* 0-365 day of year */
int tm_isdst; /* flag: daylight savings time in effect */
char **tm_zone; /* abbreviation of timezone name */
long tm_gmtoff; /* offset from GMT in seconds */
\fITm_isdst\fP is non-zero if a time zone adjustment such as Daylight
Savings time is in effect.
\fITm_gmtoff\fP is the offset (in seconds) of the time represented
from GMT, with positive values indicating East of Greenwich.
\fITimezone\fP remains for compatibility reasons only; it's impossible
to reliably map timezone's arguments (a "minutes west of GMT" value and
a "daylight saving time in effect" flag) to a time zone abbreviation.
Its current effect is to return the time zone abbreviation associated
with local time no matter what its arguments, which is probably what people
wanted anyway. Programs that in the past used the timezone function
should examine \fIlocaltime(&clock)->tm_zone\fP to find the correct time
zone abbreviation to use.
.ta \w'/etc/zoneinfo/localtime\0\0'u
/etc/zoneinfo time zone information directory
/etc/zoneinfo/localtime local time zone file
gettimeofday(2), getenv(3), time(3), tzfile(5)
The return values point to static data whose content is overwritten by
each call. The \fBtm_zone\fP field of a returned \fBstruct tm\fP
points to a static array of characters, which will also be overwritten
at the next call (and by calls to \fItzset\fP or \fItzsetwall\fP).
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