clock(3)

clock3

Determine processor time used

Usage

#include <time.h>

clock_t

clock(void);

Library

Standard C Library (libc, -lc)

Overview

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.

Releases

87 releases since FreeBSD 2.0.5-RELEASE; the text changed 41 times.

  1. 2.0.5
  2. 2.1.5–3.4
  3. 3.5–3.5.1
  4. 4.0
  5. 4.1–4.2
  6. 4.3–4.4
  7. 4.5
  8. 4.6–4.11
  9. 5.0–6.3
  10. 6.4
  11. 7.0
  12. 7.1
  13. 7.2
  14. 7.3
  15. 7.4
  16. 8.0
  17. 8.1
  18. 8.2
  19. 8.3
  20. 8.4
  21. 9.0
  22. 9.1
  23. 9.2
  24. 9.3
  25. 10.0
  26. 10.1
  27. 10.2
  28. 10.3
  29. 10.4
  30. 11.0
  31. 11.1
  32. 11.2
  33. 11.3
  34. 11.4
  35. 12.0
  36. 12.1
  37. 12.2
  38. 12.3
  39. 12.4
  40. 13.0–13.2
  41. 13.3–14.5
  42. 15.0–16.0

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.

From base 16.0-CURRENT-20261027-61c70dc16a79 in FreeBSD 16.0-CURRENT (2026-10-27). Parsed by carta from the page's mdoc source.