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.\" $NetBSD: tm.3,v 1.4 2011/04/14 05:45:34 jruoho Exp $
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.\" Copyright (c) 2011 Jukka Ruohonen <jruohonen@iki.fi>
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.Dd April 14, 2011
.Dt TM 3
.Os
.Sh NAME
.Nm tm
.Nd time structure
.Sh SYNOPSIS
.In time.h
.Sh DESCRIPTION
The
.In time.h
header defines the
.Vt tm
structure that contains calendar dates and time broken down into components.
The following standards-compliant fields are present:
.Bl -column -offset indent \
"Type" "Field  " "Months since January 1     "  "Range "
.It Sy Type Ta Sy Field Ta Sy Represents Ta Sy Range
.It Vt int Ta Va tm_sec Ta Seconds Ta [0, 61]
.It Vt int Ta Va tm_min Ta Minutes Ta [0, 59]
.It Vt int Ta Va tm_hour Ta Hours since midnight Ta [0, 23]
.It Vt int Ta Va tm_mday Ta Day of the month Ta [1, 31]
.It Vt int Ta Va tm_mon Ta Months since January Ta [0, 11]
.It Vt int Ta Va tm_year Ta Years since 1900 Ta
.It Vt int Ta Va tm_wday Ta Days since Sunday Ta [0,  6]
.It Vt int Ta Va tm_yday Ta Days since January 1 Ta [0, 365]
.It Vt int Ta Va tm_isdt Ta Positive if daylight savings Ta >= 0
.El
.Pp
The
.Vt tm
structure is used by various common library routines such as
.Xr mktime 3 ,
.Xr localtime 3 ,
and
.Xr strptime 3 .
All fields described above are defined in the
.St -p1003.1-2008
standard.
.Ss NetBSD Extensions
In addition, the following NetBSD-specific fields are available:
.Bl -column -offset indent \
"Type         " "Field  " "Months since January 1"
.It Sy Type Ta Sy Field Ta Sy Represents
.It Vt int Ta Va tm_gmtoff Ta Offset from UTC in seconds
.It Vt __aconst char Ta Va tm_zone Ta Timezone abbreviation
.El
.Pp
The
.Va tm_zone
and
.Va tm_gmtoff
fields exist, and are filled in by applicable library routines,
only if arrangements to do so were made when the library containing
these functions was created.
There is no guarantee that these fields will continue to exist
in this form in future releases of
. Nx .
.Pp
The
.Fa tm_gmtoff
field denotes the offset (in seconds) of the time represented
from UTC, with positive values indicating east
of the Prime Meridian.
The
.Vt tm_zone
field will become invalid and point to freed storage if the corresponding
.Va "struct tm"
was returned by
.Xr localtime_rz 3
and the
.Ft "const timezone_t"
.Fa tz
argument has been freed by
.Xr tzfree 3 .
.Sh SEE ALSO
.Xr asctime 3 ,
.Xr offtime 3 ,
.Xr timeval 3 ,
.Xr wcsftime 3
.Sh STANDARDS
The
.Vt tm
structure conforms to
.St -p1003.1-2008
with respect to the described standard structure members.