PROLOG

       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.

NAME

       mbrtowc — convert a character to a wide-character code (restartable)

SYNOPSIS

       #include <wchar.h>

       size_t mbrtowc(wchar_t *restrict pwc, const char *restrict s,
           size_t n, mbstate_t *restrict ps);

DESCRIPTION

       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 a null pointer, the mbrtowc() function shall be equivalent to the call:

           mbrtowc(NULL, "", 1, ps)

       In this case, the values of the arguments pwc and n are ignored.

       If s is not a null pointer, the mbrtowc() function shall inspect at most n bytes beginning
       at the byte pointed to by s to determine the number of bytes needed to complete  the  next
       character  (including  any  shift  sequences).  If  the  function determines that the next
       character is completed, it shall determine the value of the corresponding  wide  character
       and then, if pwc is not a null pointer, shall store that value in the object pointed to by
       pwc.  If the corresponding wide character is the null wide character, the resulting  state
       described shall be the initial conversion state.

       If  ps  is  a  null  pointer,  the mbrtowc() function shall use its own internal mbstate_t
       object, which shall be initialized at program start-up to the  initial  conversion  state.
       Otherwise,  the mbstate_t object pointed to by ps shall be used to completely describe the
       current conversion state of the associated character sequence.  The  implementation  shall
       behave as if no function defined in this volume of POSIX.1‐2017 calls mbrtowc().

       The behavior of this function is affected by the LC_CTYPE category of the current locale.

       The mbrtowc() function need not be thread-safe if called with a NULL ps argument.

       The mbrtowc() function shall not change the setting of errno if successful.

RETURN VALUE

       The mbrtowc() function shall return the first of the following that applies:

       0           If  the  next  n or fewer bytes complete the character that corresponds to the
                   null wide character (which is the value stored).

       between 1 and n inclusive
                   If the next n or fewer bytes complete a valid character (which  is  the  value
                   stored);  the  value  returned  shall be the number of bytes that complete the
                   character.

       (size_t)-2  If the next  n  bytes  contribute  to  an  incomplete  but  potentially  valid
                   character,  and  all  n bytes have been processed (no value is stored). When n
                   has at least the value of the {MB_CUR_MAX} macro, this case can only occur  if
                   s  points at a sequence of redundant shift sequences (for implementations with
                   state-dependent encodings).

       (size_t)-1  If an encoding error occurs, in which case the next n or fewer  bytes  do  not
                   contribute  to  a  complete  and valid character (no value is stored). In this
                   case, [EILSEQ] shall be stored in errno and the conversion state is undefined.

ERRORS

       The mbrtowc() function shall 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.

       The mbrtowc() function may fail if:

       EINVAL ps points to an object that contains an invalid conversion state.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       mbsinit(), mbsrtowcs()

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

COPYRIGHT

       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 .