#include <wchar.h>

       size_t mbsrtowcs(wchar_t *dest, const char **src,
                         size_t len, mbstate_t *ps);

       If  dest  is  not a NULL pointer, the mbsrtowcs() function converts the
       multibyte string *src to a wide-character string starting at dest.   At
       most  len  wide characters are written to dest.  The shift state *ps is
       updated.  The conversion is effectively performed by repeatedly calling
       mbrtowc(dest,  *src, n, ps) where n is some positive number, as long as
       this call succeeds, and then incrementing dest by one and *src  by  the
       number of bytes consumed.  The conversion can stop for three reasons:

       1. An  invalid  multibyte  sequence has been encountered.  In this case
          *src is left pointing to the invalid multibyte sequence, (size_t) -1
          is returned, and errno is set to EILSEQ.

       2. len  non-L'\0'  wide  characters  have been stored at dest.  In this
          case *src is left pointing to the next multibyte sequence to be con-
          verted,  and  the  number  of  wide  characters  written  to dest is

       3. The multibyte string has been completely  converted,  including  the
          terminating null wide character ('\0'), which has the side effect of
          bringing back *ps to the initial state.  In this case *src is set to
          NULL,  and  the number of wide characters written to dest, excluding
          the terminating null wide character, is returned.

       If dest is NULL, len is ignored, and the conversion proceeds as  above,
       except  that  the converted wide characters are not written out to mem-
       ory, and that no length limit exists.

       In both of the above cases, if ps is a NULL pointer, a static anonymous
       state known only to the mbsrtowcs() function is used instead.

       The  programmer  must  ensure  that there is room for at least len wide
       characters at dest.

       The mbsrtowcs() function returns the number  of  wide  characters  that
       make  up the converted part of the wide-character string, not including
       the terminating null wide character.  If an invalid multibyte  sequence
       was encountered, (size_t) -1 is returned, and errno set to EILSEQ.


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

GNU                               2011-09-28                      MBSRTOWCS(3)
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