man3/mbstowcs.3

   1 .\" Copyright (c) Bruno Haible <haible@clisp.cons.org>
   2 .\" and Copyright 2014 Michael Kerrisk <mtk.manpages@gmail.com>
   3 .\"
   4 .\" SPDX-License-Identifier: GPL-2.0-or-later
   5 .\"
   6 .\" References consulted:
   7 .\"   GNU glibc-2 source code and manual
   8 .\"   Dinkumware C library reference http://www.dinkumware.com/
   9 .\"   OpenGroup's Single UNIX specification http://www.UNIX-systems.org/online.html
  10 .\"   ISO/IEC 9899:1999
  11 .\"
  12 .TH MBSTOWCS 3  2021-03-22 "Linux man-pages (unreleased)"
  13 .SH NAME
  14 mbstowcs \- convert a multibyte string to a wide-character string
  15 .SH LIBRARY
  16 Standard C library
  17 .RI ( libc ", " \-lc )
  18 .SH SYNOPSIS
  19 .nf
  20 .B #include <stdlib.h>
  21 .PP
  22 .BI "size_t mbstowcs(wchar_t *restrict " dest ", const char *restrict " src ,
  23 .BI "                size_t " n );
  24 .fi
  25 .SH DESCRIPTION
  26 If
  27 .I dest
  28 is not NULL,
  29 the
  30 .BR mbstowcs ()
  31 function converts the
  32 multibyte string
  33 .I src
  34 to a wide-character string starting at
  35 .IR dest .
  36 At most
  37 .I n
  38 wide characters are written to
  39 .IR dest .
  40 The sequence of characters in the string
  41 .I src
  42 shall begin in the initial shift state.
  43 The conversion can stop for three reasons:
  44 .IP 1. 3
  45 An invalid multibyte sequence has been encountered.
  46 In this case,
  47 .I (size_t)\ \-1
  48 is returned.
  49 .IP 2.
  50 .I n
  51 non-L\(aq\e0\(aq wide characters have been stored at
  52 .IR dest .
  53 In this case, the number of wide characters written to
  54 .I dest
  55 is returned, but the
  56 shift state at this point is lost.
  57 .IP 3.
  58 The multibyte string has been completely converted, including the
  59 terminating null character (\(aq\e0\(aq).
  60 In this case, the number of wide characters written to
  61 .IR dest ,
  62 excluding the terminating null wide character, is returned.
  63 .PP
  64 The programmer must ensure that there is room for at least
  65 .I n
  66 wide
  67 characters at
  68 .IR dest .
  69 .PP
  70 If
  71 .I dest
  72 is NULL,
  73 .I n
  74 is ignored, and the conversion proceeds as
  75 above, except that the converted wide characters are not written out to memory,
  76 and that no length limit exists.
  77 .PP
  78 In order to avoid the case 2 above, the programmer should make sure
  79 .I n
  80 is
  81 greater than or equal to
  82 .IR "mbstowcs(NULL,src,0)+1" .
  83 .SH RETURN VALUE
  84 The
  85 .BR mbstowcs ()
  86 function returns the number of wide characters that make
  87 up the converted part of the wide-character string, not including the
  88 terminating null wide character.
  89 If an invalid multibyte sequence was
  90 encountered,
  91 .I (size_t)\ \-1
  92 is returned.
  93 .SH ATTRIBUTES
  94 For an explanation of the terms used in this section, see
  95 .BR attributes (7).
  96 .ad l
  97 .nh
  98 .TS
  99 allbox;
 100 lbx lb lb
 101 l l l.
 102 Interface       Attribute       Value
 103 T{
 104 .BR mbstowcs ()
 105 T}      Thread safety   MT-Safe
 106 .TE
 107 .hy
 108 .ad
 109 .sp 1
 110 .SH STANDARDS
 111 POSIX.1-2001, POSIX.1-2008, C99.
 112 .SH NOTES
 113 The behavior of
 114 .BR mbstowcs ()
 115 depends on the
 116 .B LC_CTYPE
 117 category of the
 118 current locale.
 119 .PP
 120 The function
 121 .BR mbsrtowcs (3)
 122 provides a better interface to the same
 123 functionality.
 124 .SH EXAMPLES
 125 The program below illustrates the use of
 126 .BR mbstowcs (),
 127 as well as some of the wide character classification functions.
 128 An example run is the following:
 129 .PP
 130 .in +4n
 131 .EX
 132 $ ./t_mbstowcs de_DE.UTF\-8 Grüße!
 133 Length of source string (excluding terminator):
 134     8 bytes
 135     6 multibyte characters
 136
 137 Wide character string is: Grüße! (6 characters)
 138     G alpha upper
 139     r alpha lower
 140     ü alpha lower
 141     ß alpha lower
 142     e alpha lower
 143     ! !alpha
 144 .EE
 145 .in
 146 .SS Program source
 147 \&
 148 .EX
 149 #include <wctype.h>
 150 #include <locale.h>
 151 #include <wchar.h>
 152 #include <stdio.h>
 153 #include <string.h>
 154 #include <stdlib.h>
 155
 156 int
 157 main(int argc, char *argv[])
 158 {
 159     size_t mbslen;      /* Number of multibyte characters in source */
 160     wchar_t *wcs;       /* Pointer to converted wide character string */
 161
 162     if (argc < 3) {
 163         fprintf(stderr, "Usage: %s <locale> <string>\en", argv[0]);
 164         exit(EXIT_FAILURE);
 165     }
 166
 167     /* Apply the specified locale. */
 168
 169     if (setlocale(LC_ALL, argv[1]) == NULL) {
 170         perror("setlocale");
 171         exit(EXIT_FAILURE);
 172     }
 173
 174     /* Calculate the length required to hold argv[2] converted to
 175        a wide character string. */
 176
 177     mbslen = mbstowcs(NULL, argv[2], 0);
 178     if (mbslen == (size_t) \-1) {
 179         perror("mbstowcs");
 180         exit(EXIT_FAILURE);
 181     }
 182
 183     /* Describe the source string to the user. */
 184
 185     printf("Length of source string (excluding terminator):\en");
 186     printf("    %zu bytes\en", strlen(argv[2]));
 187     printf("    %zu multibyte characters\en\en", mbslen);
 188
 189     /* Allocate wide character string of the desired size.  Add 1
 190        to allow for terminating null wide character (L\(aq\e0\(aq). */
 191
 192     wcs = calloc(mbslen + 1, sizeof(*wcs));
 193     if (wcs == NULL) {
 194         perror("calloc");
 195         exit(EXIT_FAILURE);
 196     }
 197
 198     /* Convert the multibyte character string in argv[2] to a
 199        wide character string. */
 200
 201     if (mbstowcs(wcs, argv[2], mbslen + 1) == (size_t) \-1) {
 202         perror("mbstowcs");
 203         exit(EXIT_FAILURE);
 204     }
 205
 206     printf("Wide character string is: %ls (%zu characters)\en",
 207             wcs, mbslen);
 208
 209     /* Now do some inspection of the classes of the characters in
 210        the wide character string. */
 211
 212     for (wchar_t *wp = wcs; *wp != 0; wp++) {
 213         printf("    %lc ", (wint_t) *wp);
 214
 215         if (!iswalpha(*wp))
 216             printf("!");
 217         printf("alpha ");
 218
 219         if (iswalpha(*wp)) {
 220             if (iswupper(*wp))
 221                 printf("upper ");
 222
 223             if (iswlower(*wp))
 224                 printf("lower ");
 225         }
 226
 227         putchar(\(aq\en\(aq);
 228     }
 229
 230     exit(EXIT_SUCCESS);
 231 }
 232 .EE
 233 .SH SEE ALSO
 234 .BR mblen (3),
 235 .BR mbsrtowcs (3),
 236 .BR mbtowc (3),
 237 .BR wcstombs (3),
 238 .BR wctomb (3)