timeradd, timersub, timercmp, timerclear, timerisset — timeval operations


#include <sys/time.h>
void timeradd( struct timeval *a,
  struct timeval *b,
  struct timeval *res);
void timersub( struct timeval *a,
  struct timeval *b,
  struct timeval *res);
void timerclear( struct timeval *tvp);
int timerisset( struct timeval *tvp);
int timercmp( struct timeval *a,
  struct timeval *b,
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
All functions shown above:
Since glibc 2.19:
_DEFAULT_SOURCE Glibc 2.19 and earlier:


The macros are provided to operate on timeval structures, defined in <sys/time.h> as:

struct timeval {
  time_t   tv_sec;
/* seconds */
  suseconds_t   tv_usec;
/* microseconds */

timeradd() adds the time values in a and b, and places the sum in the timeval pointed to by res. The result is normalized such that res−>tv_usec has a value in the range 0 to 999,999.

timersub() subtracts the time value in b from the time value in a, and places the result in the timeval pointed to by res. The result is normalized such that res−>tv_usec has a value in the range 0 to 999,999.

timerclear() zeros out the timeval structure pointed to by tvp, so that it represents the Epoch: 1970-01-01 00:00:00 +0000 (UTC).

timerisset() returns true (nonzero) if either field of the timeval structure pointed to by tvp contains a nonzero value.

timercmp() compares the timer values in a and b using the comparison operator CMP, and returns true (nonzero) or false (0) depending on the result of the comparison. Some systems (but not Linux/glibc), have a broken timercmp() implementation, in which CMP of >=, <=, and == do not work; portable applications can instead use

!timercmp(..., <) !timercmp(..., >) !timercmp(..., !=)


timerisset() and timercmp() return true (nonzero) or false (0).


No errors are defined.


Not in POSIX.1. Present on most BSD derivatives.


gettimeofday(2), time(7)


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  Copyright (c) 2007 by Michael Kerrisk <>

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2007-07-31, mtk, Created