man3/strnlen.3

   1 .\" Copyright (c) Bruno Haible <haible@clisp.cons.org>
   2 .\"
   3 .\" SPDX-License-Identifier: GPL-2.0-or-later
   4 .\"
   5 .\" References consulted:
   6 .\"   GNU glibc-2 source code and manual
   7 .\"
   8 .TH STRNLEN 3  2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
   9 .SH NAME
  10 strnlen \- determine the length of a fixed-size string
  11 .SH LIBRARY
  12 Standard C library
  13 .RI ( libc ", " \-lc )
  14 .SH SYNOPSIS
  15 .nf
  16 .B #include <string.h>
  17 .PP
  18 .BI "size_t strnlen(const char *" s ", size_t " maxlen );
  19 .fi
  20 .PP
  21 .RS -4
  22 Feature Test Macro Requirements for glibc (see
  23 .BR feature_test_macros (7)):
  24 .RE
  25 .PP
  26 .BR strnlen ():
  27 .nf
  28     Since glibc 2.10:
  29         _POSIX_C_SOURCE >= 200809L
  30     Before glibc 2.10:
  31         _GNU_SOURCE
  32 .fi
  33 .SH DESCRIPTION
  34 The
  35 .BR strnlen ()
  36 function returns the number of bytes in the string
  37 pointed to by
  38 .IR s ,
  39 excluding the terminating null byte (\(aq\e0\(aq),
  40 but at most
  41 .IR maxlen .
  42 In doing this,
  43 .BR strnlen ()
  44 looks only at the first
  45 .I maxlen
  46 characters in the string pointed to by
  47 .I s
  48 and never beyond
  49 .IR s[maxlen\-1] .
  50 .SH RETURN VALUE
  51 The
  52 .BR strnlen ()
  53 function returns
  54 .IR strlen(s) ,
  55 if that is less than
  56 .IR maxlen ,
  57 or
  58 .I maxlen
  59 if there is no null terminating (\(aq\e0\(aq) among the first
  60 .I maxlen
  61 characters pointed to by
  62 .IR s .
  63 .SH ATTRIBUTES
  64 For an explanation of the terms used in this section, see
  65 .BR attributes (7).
  66 .ad l
  67 .nh
  68 .TS
  69 allbox;
  70 lbx lb lb
  71 l l l.
  72 Interface       Attribute       Value
  73 T{
  74 .BR strnlen ()
  75 T}      Thread safety   MT-Safe
  76 .TE
  77 .hy
  78 .ad
  79 .sp 1
  80 .SH STANDARDS
  81 POSIX.1-2008.
  82 .SH SEE ALSO
  83 .BR strlen (3)