#include <stdlib.h>

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

       If  dest  is  not  NULL, 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 than 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.

       For   an   explanation   of   the  terms  used  in  this  section,  see

       |Interface  | Attribute     | Value   |
       |mbstowcs() | Thread safety | MT-Safe |
       POSIX.1-2001, POSIX.1-2008, C99.

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

           Wide character string is: GruBe! (6 characters)
               G alpha upper
               r alpha lower
               u alpha lower
               B alpha lower
               e alpha lower
               ! !alpha

   Program source
       #include <locale.h>
       #include <wchar.h>
       #include <stdio.h>
       #include <string.h>
       #include <stdlib.h>

       main(int argc, char *argv[])
           size_t mbslen;      /* Number of multibyte characters in source */
           wchar_t *wcs;       /* Pointer to converted wide character string */
           wchar_t *wp;

           if (argc < 3) {
               fprintf(stderr, "Usage: %s <locale> <string>\n", argv[0]);

           /* Apply the specified locale */

           if (setlocale(LC_ALL, argv[1]) == NULL) {

           /* Calculate the length required to hold argv[2] converted to
              a wide character string */

           mbslen = mbstowcs(NULL, argv[2], 0);
           if (mbslen == (size_t) -1) {

           /* Describe the source string to the user */

           printf("Length of source string (excluding terminator):\n");
           printf("    %zu bytes\n", strlen(argv[2]));
           printf("    %zu multibyte characters\n\n", mbslen);

           /* Allocate wide character string of the desired size.  Add 1
              to allow for terminating null wide character (L'\0'). */

           wcs = calloc(mbslen + 1, sizeof(wchar_t));

           printf("Wide character string is: %ls (%zu characters)\n",
                   wcs, mbslen);

           /* Now do some inspection of the classes of the characters in
              the wide character string */

           for (wp = wcs; *wp != 0; wp++) {
               printf("    %lc ", (wint_t) *wp);

               if (!iswalpha(*wp))
               printf("alpha ");

               if (iswalpha(*wp)) {
                   if (iswupper(*wp))
                       printf("upper ");

                   if (iswlower(*wp))
                       printf("lower ");



       mblen(3), mbsrtowcs(3), mbtowc(3), wctomb(3), wcstombs(3)

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GNU                               2015-08-08                       MBSTOWCS(3)
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