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.TH CTIME 2
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.SH NAME
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ctime, localtime, gmtime, asctime, tm2sec, timezone \- convert date and time
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.ta \w'\fLchar* 'u
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.B
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char*	ctime(long clock)
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.PP
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.B
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Tm*	localtime(long clock)
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.PP
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.B
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Tm*	gmtime(long clock)
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.PP
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.B
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char*	asctime(Tm *tm)
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.PP
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.B
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long	tm2sec(Tm *tm)
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.PP
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.B
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/env/timezone
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.SH DESCRIPTION
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.I Ctime
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converts a time
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.I clock
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such as returned by
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.IR time (2)
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into
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.SM ASCII
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(sic)
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and returns a pointer to a
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30-byte string
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in the following form.
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All the fields have constant width.
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.PP
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.B
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	Wed Aug  5 01:07:47 EST 1973\en\e0
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.PP
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.I Localtime
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and
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.I gmtime
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return pointers to structures containing
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the broken-down time.
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.I Localtime
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corrects for the time zone and possible daylight savings time;
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.I gmtime
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converts directly to GMT.
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.I Asctime
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converts a broken-down time to
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.SM ASCII
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and returns a pointer
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to a 30-byte string.
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.IP
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.EX
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.ta 6n +\w'char 'u +\w'zone[4];    'u
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typedef
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struct {
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	int	sec;	/* seconds (range 0..59) */
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	int	min;	/* minutes (0..59) */
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	int	hour;	/* hours (0..23) */
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	int	mday;	/* day of the month (1..31) */
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	int	mon;	/* month of the year (0..11) */
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	int	year;	/* year A.D. \- 1900 */
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	int	wday;	/* day of week (0..6, Sunday = 0) */
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	int	yday;	/* day of year (0..365) */
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	char	zone[4];	/* time zone name */
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	int	tzoff;	/* time zone delta from GMT */
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} Tm;
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.EE
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.PP
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.I Tm2sec
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converts a broken-down time to
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seconds since the start of the epoch.
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It ignores
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.BR wday ,
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and assumes the local time zone
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if
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.B zone
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is not
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.BR GMT .
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.PP
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When local time is first requested,
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the program consults the
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.B timezone
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environment variable to determine the time zone and
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converts accordingly.
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(This variable is set at system boot time by
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.IR init (8).)
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The
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.B timezone
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variable contains
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the normal time zone name and its difference from GMT
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in seconds followed by an alternate (daylight) time zone name and
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its difference followed by a newline.
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The remainder is a list of pairs of times
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(seconds past the start of 1970, in the first time zone)
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when the alternate time zone applies.
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For example:
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.IP
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.EX
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EST -18000 EDT -14400
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 9943200 25664400 41392800 57718800 ...
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.EE
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.PP
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Greenwich Mean Time is represented by
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.IP
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.EX
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GMT 0
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.EE
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.SH SOURCE
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.B /sys/src/libc/9sys
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.SH "SEE ALSO"
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.IR date (1),
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.IR time (2),
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.IR init (8)
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.SH BUGS
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The return values point to static data
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whose content is overwritten by each call.
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.br
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Daylight Savings Time is ``normal'' in the Southern hemisphere.
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.br
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These routines are not equipped to handle non-\c
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.SM ASCII
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text, and are provincial anyway.