'\" t
.\" Copyright, Bruno Haible <bruno@clisp.org>
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: GPL-2.0-or-later
.\"
.TH strnlen 3 2026-08-10 "Linux man-pages 6.19"
.SH NAME
strnlen \- nonstring length
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.BR #include\~<string.h> "  // see memory.h(3head)"
.P
.BR "size_t strnlen(const char " strn "[], size_t " n );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR strnlen ():
.nf
    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _GNU_SOURCE
.fi
.SH DESCRIPTION
This function
determines the length of the character sequence
contained in the array pointed to by
.IR strn .
.P
If
.I strn
contains a string,
the array can have less than
.I n
elements.
.P
It is equivalent to
.P
.in +4n
.EX
(memchr(strn, \[aq]\[rs]0\[aq], n) ?: strn + n) - strn
.EE
.in
.SH RETURN VALUE
The
.BR strnlen ()
function returns the number of nonnull characters in
.IR strn .
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR strnlen ()
T}	Thread safety	MT-Safe
.TE
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
POSIX.1-2008.
.SH SEE ALSO
.BR memory.h (3head)