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.\" $NetBSD: offtime.3,v 1.3 2011/04/14 05:50:50 jruoho Exp $
.\" Written by Klaus Klein, May 10, 2004.
.\" Public domain.
.Dd April 14, 2011
.Dt OFFTIME 3
.Os
.Sh NAME
.Nm offtime ,
.Nm timeoff ,
.Nm timegm ,
.Nm timelocal
.Nd convert date and time
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In time.h
.Ft struct tm *
.Fn offtime "const time_t * clock" "long int offset"
.Ft struct tm *
.Fn offtime_r "const time_t * clock" "long int offset" "struct tm *ret"
.Ft time_t
.Fn timeoff "struct tm * tm" "long int offset"
.Ft time_t
.Fn timegm "struct tm * tm"
.Ft time_t
.Fn timelocal "struct tm * tm"
.Sh DESCRIPTION
These functions are inspired by C standard interfaces named similarly.
.Pp
.Fn offtime
converts the calendar time
.Fa clock ,
offset by
.Fa offset
seconds,
into broken-down time, expressed as Coordinated Universal Time (UTC).
.Pp
.Fn offtime_r
is similar to
.Fn offtime
but it places the returned
.Ft "struct tm *"
in the user supplied
.Fa ret
argument.
.Pp
.Fn timeoff
converts the broken-down time
.Fa tm ,
expressed as UTC,
offset by
.Fa offset
seconds,
into a calendar time value.
.Pp
.Fn timegm
converts the broken-down time
.Fa tm
into a calendar time value, effectively being the inverse of
.Xr gmtime 3 .
It is equivalent to the C standard function
.Xr mktime 3
operating in UTC.
.Pp
.Fn timelocal
converts the broken down time
.Fa tm ,
expressed as local time, into a calendar time value.
It is equivalent to the C standard function
.Xr mktime 3 ,
and is provided for symmetry only.
.Sh SEE ALSO
.Xr ctime 3 ,
.Xr tm 3 ,
.Xr tzset 3
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