#include <stdlib.h>

       size_t mbstowcs(wchar_t *dest, const char *src, size_t n);

       If  dest  is  not  a NULL pointer, the mbstowcs() function converts the
       multibyte string src to a wide-character string starting at  dest.   At
       most  n  wide characters are written to dest.  The conversion starts in
       the initial state.  The conversion can stop for three reasons:

       1. An invalid multibyte sequence has been encountered.   In  this  case
          (size_t) -1 is returned.

       2. n  non-L'\0' wide characters have been stored at dest.  In this case
          the number of wide characters written to dest is returned,  but  the
          shift state at this point is lost.

       3. The  multibyte  string  has been completely converted, including the
          terminating null wide character ('\0').  In this case the number  of
          wide characters written to dest, excluding the terminating null wide
          character, is returned.

       The programmer must ensure that there is room for at least n wide char-
       acters at dest.

       If  dest  is  NULL, n 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  order  to avoid the case 2 above, the programmer should make sure n
       is greater or equal to mbstowcs(NULL,src,0)+1.

       The mbstowcs() 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.


       The behavior of mbstowcs() depends on the LC_CTYPE category of the cur-
       rent locale.

       The function mbsrtowcs(3) provides a better interface to the same func-

       mbsrtowcs(3), wcstombs(3)

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