NAME

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

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdlib.h>

       size_t mbstowcs(wchar_t dest[restrict .dsize], const char *restrict src,
                       size_t dsize);

DESCRIPTION

       If  dest is not NULL, convert the multibyte string src to a wide-character string starting
       at dest.  At most dsize 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.

       •  dsize  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.

       If dest is NULL, dsize 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 dsize is greater than
       or equal to mbstowcs(NULL,src,0)+1.

       The programmer must ensure that there is room for at least dsize wide characters at dest.

RETURN VALUE

       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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

VERSIONS

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

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       POSIX.1-2001, C99.

NOTES

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

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