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                                         MBLEN(3POSIX)

       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.

       If  s  is  not  a  null  pointer,  mblen() shall determine the number of bytes constituting the character
       pointed to by s.  Except that the shift state of mbtowc() is not affected, it shall be equivalent to:

           mbtowc((wchar_t *)0, s, n);

       The implementation shall behave as if no function defined in this volume of POSIX.1‐2017 calls mblen().

       The behavior of this function is affected by the LC_CTYPE category of the current locale.  For  a  state-
       dependent  encoding,  this  function  shall  be  placed  into  its  initial state by a call for which its
       character pointer argument, s, is a null pointer. Subsequent calls with s as other than  a  null  pointer
       shall  cause  the  internal  state  of  the  function to be altered as necessary. A call with s as a null
       pointer shall cause this function to return a non-zero value if encodings have state  dependency,  and  0
       otherwise.  If  the implementation employs special bytes to change the shift state, these bytes shall not
       produce separate wide-character codes, but shall be grouped with  an  adjacent  character.  Changing  the
       LC_CTYPE category causes the shift state of this function to be unspecified.

       The mblen() function need not be thread-safe.

       The mblen() function may fail if:

       EILSEQ An  invalid  character  sequence  is  detected. In the POSIX locale an [EILSEQ] error cannot occur
              since all byte values are valid characters.

       Thefollowingsectionsareinformative.

       None.

       None.

       mblen — get number of bytes in a character

       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.

       If s is a null pointer, mblen() shall return a non-zero or 0 value, if character encodings, respectively,
       do  or  do  not have state-dependent encodings. If s is not a null pointer, mblen() shall either return 0
       (if s points to the null byte), or return the number of bytes that constitute the character (if the  next
       n  or  fewer  bytes form a valid character), or return -1 (if they do not form a valid character) and may
       set errno to indicate the error.  In no case shall the value returned be greater than n or the  value  of
       the {MB_CUR_MAX} macro.

mbtowc(), mbstowcs(), wctomb(), wcstombs()

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

       #include <stdlib.h>

       int mblen(const char *s, size_t n);