man3/strnlen.3

.\" Copyright (c) Bruno Haible <haible@clisp.cons.org>
.\"
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.\" References consulted:
.\"   GNU glibc-2 source code and manual
.\"
.TH STRNLEN 3  2021-03-22 "GNU" "Linux Programmer's Manual"
.SH NAME
strnlen \- determine the length of a fixed-size string
.SH SYNOPSIS
.nf
.B #include <string.h>
.PP
.BI "size_t strnlen(const char *" s ", size_t " maxlen );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR strnlen ():
.nf
    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _GNU_SOURCE
.fi
.SH DESCRIPTION
The
.BR strnlen ()
function returns the number of bytes in the string
pointed to by
.IR s ,
excluding the terminating null byte (\(aq\e0\(aq),
but at most
.IR maxlen .
In doing this,
.BR strnlen ()
looks only at the first
.I maxlen
characters in the string pointed to by
.I s
and never beyond
.IR s[maxlen\-1] .
.SH RETURN VALUE
The
.BR strnlen ()
function returns
.IR strlen(s) ,
if that is less than
.IR maxlen ,
or
.I maxlen
if there is no null terminating (\(aq\e0\(aq) among the first
.I maxlen
characters pointed to by
.IR s .
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR strnlen ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
POSIX.1-2008.
.SH SEE ALSO
.BR strlen (3)