strlen(3) — Linux manual page

strlen(3)                Library Functions Manual               strlen(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

       The strlen() function calculates the length of the string pointed
       to by s, excluding the terminating null byte ('\0').

       It is equivalent to

           strnul(s) - s

RETURN VALUE         top

       The strlen() function returns the number of bytes in the string
       pointed to by s.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(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), strnul(3), wcslen(3), wcsnlen(3)

COLOPHON         top

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Linux man-pages 6.18            2026-02-25                      strlen(3)

Pages that refer to this page: audit_encode_nv_string(3),  audit_encode_value(3),  lber-types(3),  pmfstring(3),  rawmemchr(3),  strchr(3),  string(3),  strnlen(3),  strnul(3),  wcslen(3),  signal-safety(7)

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