---
name: "clock"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/clock/3"
---

# clock(3)

determine processor time used

## NAME

**clock** – determine processor time used

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<time.h\>**

*clock\_t*\

**clock**(*void*);

## DESCRIPTION

The **clock**() function determines the amount of processor time used since the invocation of the calling process, measured in CLOCKS\_PER\_SECs of a second.

## RETURN VALUES

The **clock**() function returns the amount of time used unless an error occurs, in which case the return value is -1.

## SEE ALSO

[getrusage(2)](/getrusage/2.md), [clocks(7)](/clocks/7.md)

## STANDARDS

The **clock**() function conforms to ISO/IEC 9899:1990 (“ISO C90”). However, Version 2 of the Single UNIX Specification (“SUSv2”) requires CLOCKS\_PER\_SEC to be defined as one million. FreeBSD does not conform to this requirement; changing the value would introduce binary incompatibility and one million is still inadequate on modern processors.