strnlen(3)                 Library Functions Manual                 strnlen(3)

NAME
       strnlen - nonstring length

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <string.h>  // see memory.h(3head)

       size_t strnlen(const char strn[], size_t n);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       strnlen():
           Since glibc 2.10:
               _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
               _GNU_SOURCE

DESCRIPTION
       This function determines the length of the character sequence contained
       in the array pointed to by strn.

       If strn contains a string, the array can have less than n elements.

       It is equivalent to

           (memchr(strn, '\0', n) ?: strn + n) - strn

RETURN VALUE
       The strnlen() function returns the number of nonnull characters in
       strn.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |strnlen ()                                  | Thread safety | MT-Safe |
       +--------------------------------------------+---------------+---------+
STANDARDS
       POSIX.1-2008.

HISTORY
       POSIX.1-2008.

SEE ALSO
       memory.h(3head)

Linux man-pages 6.19              2026-08-10                        strnlen(3)