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strlen(3) — Linux manual page

strlen(3)                Library Functions Manualstrlen(3)

NAME        top

       strlen - calculate the length of a string

LIBRARY        top

       Standard C library (libc,-lc)

SYNOPSIS        top

#include <string.h>size_t strlen(const char *s);

DESCRIPTION        top

       Thestrlen() function calculates the length of the string pointed       to bys, excluding the terminating null byte ('\0').

RETURN VALUE        top

       Thestrlen() function returns the number of bytes in the string       pointed to bys.

ATTRIBUTES        top

       For an explanation of the terms used in this section, seeattributes(7).       ┌──────────────────────────────────────┬───────────────┬─────────┐       │Interface│Attribute│Value│       ├──────────────────────────────────────┼───────────────┼─────────┤       │strlen()                             │ Thread safety │ MT-Safe │       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS        top

       C11, POSIX.1-2008.

HISTORY        top

       POSIX.1-2001, C89, SVr4, 4.3BSD.

NOTES        top

       In cases where the input buffer may not contain a terminating null       byte,strnlen(3) should be used instead.

SEE ALSO        top

string(3),strnlen(3),wcslen(3),wcsnlen(3)

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17strlen(3)

Pages that refer to this page:lber-types(3), memchr(3), pmfstring(3), regex(3), strchr(3), string(3), strnlen(3), wcslen(3), signal-safety(7)

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