focal (3) mbstowcs.3.gz

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NAME

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

SYNOPSIS

       #include <stdlib.h>

       size_t mbstowcs(wchar_t *dest, const char *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).

       ┌───────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├───────────┼───────────────┼─────────┤
       │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.

EXAMPLE

       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 */
           wchar_t *wp;

           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(wchar_t));
           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 (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

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