NAME

       mbtowc - convert a multibyte sequence to a wide character

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdlib.h>

       int mbtowc(size_t size;
                  wchar_t *restrict pwc, const char s[restrict size],
                  size_t size);

DESCRIPTION

       The  main  case  for this function is when s is not NULL and pwc is not NULL.  In this case, the mbtowc()
       function inspects at most size bytes of the multibyte string starting at s, extracts  the  next  complete
       multibyte character, converts it to a wide character and stores it at *pwc.  It updates an internal shift
       state  known  only  to  the mbtowc() function.  If s does not point to a null byte ('\0'), it returns the
       number of bytes that were consumed from s, otherwise it returns 0.

       If the size bytes starting at s do not contain a complete multibyte character,  or  if  they  contain  an
       invalid  multibyte  sequence,  mbtowc()  returns  -1.  This can happen even if size >= MB_CUR_MAX, if the
       multibyte string contains redundant shift sequences.

       A different case is when s is not NULL but pwc is NULL.  In this case, the mbtowc() function  behaves  as
       above, except that it does not store the converted wide character in memory.

       A  third  case  is when s is NULL.  In this case, pwc and size are ignored.  The mbtowc() function resets
       the shift state, only known to this function, to the initial state, and returns nonzero if  the  encoding
       has nontrivial shift state, or zero if the encoding is stateless.

RETURN VALUE

       If  s  is  not  NULL, the mbtowc() function returns the number of consumed bytes starting at s, or 0 if s
       points to a null byte, or -1 upon failure.

       If s is NULL, the mbtowc() function returns nonzero if the encoding has nontrivial shift state,  or  zero
       if the encoding is stateless.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).
       ┌──────────────────────────────────────────────────────────────────────┬───────────────┬────────────────┐
       │ Interface                                                            │ Attribute     │ Value          │
       ├──────────────────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │ mbtowc()                                                             │ Thread safety │ MT-Unsafe race │
       └──────────────────────────────────────────────────────────────────────┴───────────────┴────────────────┘

VERSIONS

       This  function  is not multithread safe.  The function mbrtowc(3) provides a better interface to the same
       functionality.

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       POSIX.1-2001, C99.

NOTES

       The behavior of mbtowc() depends on the LC_CTYPE category of the current locale.

SEE ALSO

       MB_CUR_MAX(3), mblen(3), mbrtowc(3), mbstowcs(3), wcstombs(3), wctomb(3)

Linux man-pages 6.16                               2025-09-07                                          mbtowc(3)