---
name: "timeradd"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/timeradd"
---

# timeradd(3)

timeval operations

## NAME

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

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#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***,** *CMP***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

All functions shown above:

```
    Since glibc 2.19:
        _DEFAULT_SOURCE
    glibc 2.19 and earlier:
        _BSD_SOURCE
```

## DESCRIPTION

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(..., !=)
```

## RETURN VALUE

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

## ERRORS

No errors are defined.

## STANDARDS

None.

## HISTORY

BSD.

## SEE ALSO

[**gettimeofday**(2)](/gettimeofday/2.md), [**time**(7)](/time/7.md)