mbstowcs - convert a multibyte string to a wide-character string


   #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 sequence of characters in the
   string src shall begin in the initial shift 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 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
   characters 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
   memory, 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
   current locale.

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


   The program below illustrates the use of mbstowcs(), as well as some of
   the wide character classification functions.  An  example  run  is  the

       $ ./t_mbstowcs de_DE.UTF-8 Gre!
       Length of source string (excluding terminator):
           8 bytes
           6 multibyte characters

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

   Program source
   #include <wctype.h>
   #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));
       if (wcs == NULL) {

       /* Convert the multibyte character string in argv[2] to a
          wide character string */

       if (mbstowcs(wcs, argv[2], mbslen + 1) == (size_t) -1) {

       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), wcstombs(3), wctomb(3)


   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at


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