mbstowcs(3) — Linux manual page


MBSTOWCS(3)               Linux Programmer's Manual              MBSTOWCS(3)

NAME         top

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

SYNOPSIS         top

       #include <stdlib.h>

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

DESCRIPTION         top

       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.

RETURN VALUE         top

       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.

ATTRIBUTES         top

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

       │Interface  Attribute     Value   │
       │mbstowcs() │ Thread safety │ MT-Safe │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, C99.

NOTES         top

       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

EXAMPLES         top

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

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

           Wide character string is: Grüße! (6 characters)
               G alpha upper
               r alpha lower
               ü alpha lower
               ß 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 ");



SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.08 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

GNU                              2020-06-09                      MBSTOWCS(3)

Pages that refer to this page: fwprintf(3)mb_cur_max(3)MB_CUR_MAX(3)mbsrtowcs(3)mbtowc(3)swprintf(3)vfwprintf(3)vswprintf(3)vwprintf(3)wcstombs(3)wctomb(3)wprintf(3)locale(7)