strlen(3)

strlen3

Find length of string

Usage

#include <string.h>

size_t

strlen(const char *s);

size_t

strnlen(const char *s, size_t maxlen);

Library

Standard C Library (libc, -lc)

Overview

The strlen() function computes the length of the string s. The strnlen() function attempts to compute the length of s, but never scans beyond the first maxlen bytes of s.

Return values

The strlen() function returns the number of characters that precede the terminating NUL character. The strnlen() function returns either the same result as strlen() or maxlen, whichever is smaller.

Releases

87 releases since FreeBSD 2.0.5-RELEASE; the text changed 40 times.

  1. 2.0.5–3.4
  2. 3.5–3.5.1
  3. 4.0
  4. 4.1–4.2
  5. 4.3–4.4
  6. 4.5–4.11
  7. 5.0–6.3
  8. 6.4
  9. 7.0
  10. 7.1
  11. 7.2
  12. 7.3
  13. 7.4
  14. 8.0
  15. 8.1
  16. 8.2
  17. 8.3
  18. 8.4
  19. 9.0
  20. 9.1
  21. 9.2
  22. 9.3
  23. 10.0
  24. 10.1
  25. 10.2
  26. 10.3
  27. 10.4
  28. 11.0
  29. 11.1
  30. 11.2
  31. 11.3
  32. 11.4
  33. 12.0
  34. 12.1
  35. 12.2
  36. 12.3
  37. 12.4
  38. 13.0–13.1
  39. 13.2
  40. 13.3–14.5
  41. 15.0–16.0

Standards

The strlen() function conforms to ISO/IEC 9899:1990 (“ISO C90”). The strnlen() function conforms to IEEE Std 1003.1-2008 (“POSIX.1”).

History

The strlen() function first appeared in the Programmer's Workbench (PWB/UNIX) and was ported to Version 7 AT&T UNIX. The strnlen() function first appeared in FreeBSD 8.0, OpenBSD 4.8, and NetBSD 6.0.

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