4.2BSD/usr/man/man3/ctime.3

.TH CTIME 3  "26 June 1983"
.UC 4
.SH NAME
ctime, localtime, gmtime, asctime, timezone \-  convert date and time to ASCII
.SH SYNOPSIS
.nf
.B char *ctime(clock)
.B long *clock;
.PP
.B #include <sys/time.h>
.PP
.B struct tm *localtime(clock)
.B long *clock;
.PP
.B struct tm *gmtime(clock)
.B long *clock;
.PP
.B char *asctime(tm)
.B struct tm *tm;
.PP
.B char *timezone(zone, dst)
.fi
.SH DESCRIPTION
.I Ctime
converts a time pointed to by
.I clock
such as returned by
.IR time (2)
into ASCII
and returns a pointer to a
26-character string
in the following form.
All the fields have constant width.
.PP
    Sun Sep 16 01:03:52 1973\\n\\0
.PP
.I Localtime
and
.I gmtime
return pointers to structures containing
the broken-down time.
.I Localtime
corrects for the time zone and possible daylight savings time;
.I gmtime
converts directly to GMT, which is the time UNIX uses.
.I Asctime
converts a broken-down time to ASCII and returns a pointer
to a 26-character string.
.PP
The structure declaration from the include file is:
.PP
.RS
.nf
struct tm {
	int	tm_sec;
	int	tm_min;
	int	tm_hour;
	int	tm_mday;
	int	tm_mon;
	int	tm_year;
	int	tm_wday;
	int	tm_yday;
	int	tm_isdst;
};
.fi
.RE
.PP
These quantities give the time on a 24-hour clock,
day of month (1-31), month of year (0-11), day of week
(Sunday = 0), year \- 1900, day of year (0-365),
and a flag that is nonzero if daylight saving time is in effect.
.PP
When local time is called for,
the program consults the system to determine the time zone and
whether the U.S.A., Australian, Eastern European, Middle European,
or Western European daylight saving time adjustment is appropriate.
The program knows about various peculiarities in time conversion
over the past 10-20 years; if necessary, this understanding can
be extended.
.PP
.I Timezone
returns the name of the time zone associated with its first argument,
which is measured in minutes westward from Greenwich.
If the second argument is 0, the standard name is used,
otherwise the Daylight Saving version.
If the required name does not appear in a table
built into the routine,
the difference from GMT is produced; e.g.
in Afghanistan
.I timezone(-(60*4+30), 0)
is appropriate because it is 4:30 ahead of GMT
and the string
.B GMT+4:30
is produced.
.SH "SEE ALSO"
gettimeofday(2), time(3)
.SH BUGS
The return values point to static data
whose content is overwritten by each call.