mbstowcs

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



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

SYNOPSIS
       #include <stdlib.h>

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

DESCRIPTION
       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
       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
       For an explanation of the terms used in this section, see attributes(7).

       ┌──────────────────────────────────────────────┬───────────────┬─────────┐
       │Interface                                     Attribute     Value   │
       ├──────────────────────────────────────────────┼───────────────┼─────────┤
       │mbstowcs()                                    │ Thread safety │ MT-Safe │
       └──────────────────────────────────────────────┴───────────────┴─────────┘

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

NOTES
       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
       functionality.

EXAMPLES
       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>

       int
       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]);
               exit(EXIT_FAILURE);
           }

           /* Apply the specified locale. */

           if (setlocale(LC_ALL, argv[1]) == NULL) {
               perror("setlocale");
               exit(EXIT_FAILURE);
           }

           /* 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) {
               perror("mbstowcs");
               exit(EXIT_FAILURE);
           }

           /* 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) {
               perror("calloc");
               exit(EXIT_FAILURE);
           }

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

           if (mbstowcs(wcs, argv[2], mbslen + 1) == (size_t) -1) {
               perror("mbstowcs");
               exit(EXIT_FAILURE);
           }

           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("!");
               printf("alpha ");

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

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

               putchar('\n');
           }

           exit(EXIT_SUCCESS);
       }

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

COLOPHON
       This page is part of release 5.13 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
       https://www.kernel.org/doc/man-pages/.



GNU                                2021-03-22                        MBSTOWCS(3)