.\" Copyright (c) 2007 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
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.\" 2007-07-31, mtk, Created
.\"
.TH TIMERADD 3 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
timeradd, timersub, timercmp, timerclear, timerisset \- timeval operations
.SH SYNOPSIS
.nf
.B #include <sys/time.h>
.PP
.BI "void timeradd(struct timeval *" a ", struct timeval *" b ,
.BI "              struct timeval *" res );
.PP
.BI "void timersub(struct timeval *" a ", struct timeval *" b ,
.BI "              struct timeval *" res );
.PP
.BI "void timerclear(struct timeval *" tvp );
.PP
.BI "int timerisset(struct timeval *" tvp );
.PP
.BI "int timercmp(struct timeval *" a ", struct timeval *" b ", " CMP );
.fi
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
All functions shown above:
    Since glibc 2.19:
        _DEFAULT_SOURCE
    Glibc 2.19 and earlier:
        _BSD_SOURCE
.SH DESCRIPTION
The macros are provided to operate on
.I timeval
structures, defined in
.I <sys/time.h>
as:
.PP
.in +4n
.EX
struct timeval {
    time_t      tv_sec;     /* seconds */
    suseconds_t tv_usec;    /* microseconds */
};
.EE
.in
.PP
.BR timeradd ()
adds the time values in
.I a
and
.IR b ,
and places the sum in the
.I timeval
pointed to by
.IR res .
The result is normalized such that
.I res\->tv_usec
has a value in the range 0 to 999,999.
.PP
.BR timersub ()
subtracts the time value in
.I b
from the time value in
.IR a ,
and places the result in the
.I timeval
pointed to by
.IR res .
The result is normalized such that
.I res\->tv_usec
has a value in the range 0 to 999,999.
.PP
.BR timerclear ()
zeros out the
.I timeval
structure pointed to by
.IR tvp ,
so that it represents the Epoch: 1970-01-01 00:00:00 +0000 (UTC).
.PP
.BR timerisset ()
returns true (nonzero) if either field of the
.I timeval
structure pointed to by
.I tvp
contains a nonzero value.
.PP
.BR timercmp ()
compares the timer values in
.I a
and
.I b
using the comparison operator
.IR CMP ,
and returns true (nonzero) or false (0) depending on
the result of the comparison.
Some systems (but not Linux/glibc),
have a broken
.BR timercmp ()
implementation,
.\" HP-UX, Tru64, Irix have a definition like:
.\"#define timercmp(tvp, uvp, cmp) \
.\"    ((tvp)->tv_sec cmp (uvp)->tv_sec || \
.\"    (tvp)->tv_sec == (uvp)->tv_sec && (tvp)->tv_usec cmp (uvp)->tv_usec)
in which
.I CMP
of
.IR >= ,
.IR <= ,
and
.I ==
do not work;
portable applications can instead use
.PP
    !timercmp(..., <)
    !timercmp(..., >)
    !timercmp(..., !=)
.SH RETURN VALUE
.BR timerisset ()
and
.BR timercmp ()
return true (nonzero) or false (0).
.SH ERRORS
No errors are defined.
.SH CONFORMING TO
Not in POSIX.1.
Present on most BSD derivatives.
.SH SEE ALSO
.BR gettimeofday (2),
.BR time (7)
.SH COLOPHON
This page is part of release 4.16 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.