mbstowcs(3) — Linux manual page


mbstowcs(3)             Library Functions Manual             mbstowcs(3)

NAME         top

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

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <stdlib.h>

       size_t mbstowcs(wchar_t dest[restrict .n], const char *restrict 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:

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

       •  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.

       •  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 │

VERSIONS         top

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

STANDARDS         top

       C11, POSIX.1-2008.

HISTORY         top

       POSIX.1-2001, C99.

NOTES         top

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

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 <locale.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>
       #include <wchar.h>
       #include <wctype.h>

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

           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(*wcs));
           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 (wchar_t *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)

Linux man-pages (unreleased)     (date)                      mbstowcs(3)

Pages that refer to this page: MB_CUR_MAX(3)mbsrtowcs(3)mbtowc(3)wcstombs(3)wctomb(3)wprintf(3)locale(7)