This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       None.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                        STRLEN(3POSIX)

       For  strlen(): The functionality described on this reference page is aligned with the ISO C standard. Any
       conflict between the requirements described here and the ISO C standard is unintentional. This volume  of
       POSIX.1‐2017 defers to the ISO C standard.

       The  strlen()  function  shall compute the number of bytes in the string to which s points, not including
       the terminating NUL character.

       The strnlen() function shall compute the smaller of the number of bytes in the array to which  s  points,
       not  including any terminating NUL character, or the value of the maxlen argument. The strnlen() function
       shall never examine more than maxlen bytes of the array pointed to by s.

       No errors are defined.

       Thefollowingsectionsareinformative.

GettingStringLengths
       The  following  example  sets  the maximum length of key and data by using strlen() to get the lengths of
       those strings.

           #include <string.h>
           ...
           struct element {
               char *key;
               char *data;
           };
           ...
           char *key, *data;
           int len;

           *keylength = *datalength = 0;
           ...
           if ((len = strlen(key)) > *keylength)
               *keylength = len;
           if ((len = strlen(data)) > *datalength)
               *datalength = len;
           ...

       None.

       strlen, strnlen — get length of fixed size string

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

       None.

       The strlen() function shall return the length of s; no return value shall  be  reserved  to  indicate  an
       error.

       The  strnlen()  function  shall  return the number of bytes preceding the first null byte in the array to
       which s points, if s contains a null byte within the first  maxlen  bytes;  otherwise,  it  shall  return
       maxlen.

wcslen()

       The Base Definitions volume of POSIX.1‐2017, <string.h>

       #include <string.h>

       size_t strlen(const char *s);
       size_t strnlen(const char *s, size_t maxlen);