Chapter 6. LOCALE technology

58

You cannot assume anything on the concrete value of

wchar_t

, besides

0x21

0x7e

are identi 

cal to ASCII.

3

You may feel this limitation is too strong. If you cannot do under this limitation,

you can use UCS 4 as the internal encoding. In such a case, you can write your software emulat 

ing the locale sensible behavior using

setlocale()

,

nl_langinfo(CODESET)

, and

iconv()

.

Consult the section of `

nl_langinfo()

and

iconv()

' on the next page. Note that it is generally

easier to use wide character than implement UCS 4 or UTF 8.

You can write wide character in the source code as

L'a'

and wide string as

L string 

. Since

the encoding for the source code is ASCII, you can only write ASCII characters. If you'd like to

use other characters, you should use

gettext

.

There are two ways to use wide characters:

  I/O is described using multibyte characters. Inputed data are converted into wide char 

acter immediately after reading and data for output are converted from wide character to

multibyte character immediately before writing. Conversion can be achieved using func 

tions of

mbstowcs()

,

mbsrtowcs()

,

wcstombs()

,

wcsrtombs()

,

mblen()

,

mbrlen()

,

mbsinit()

, and so on. Please consult the manual pages for these functions.

  Wide characters are directly used for I/O, using wide character functions such as

getwchar()

,

fgetwc()

,

getwc()

,

ungetwc()

,

fgetws

,

putwchar()

,

fputwc()

,

putwc()

, and

fputws()

,

formatted I/O functions for wide characters such as

fwscanf()

,

wscanf()

,

swscanf()

,

fwprintf()

,

wprintf()

,

swprintf()

,

vfwprintf()

,

vwprintf()

, and

vswprintf()

,

and wide character identifier of

%lc

,

%C

,

%ls

,

%S

for conventional formatted I/O functions.

By using this approach, you don't need to handle multibyte characters at all. Please consult

the manual pages for these functions.

Though latter functions are also determined in ISO C, these functions have became newly avail 

able since GNU libc 2.2. (Of course all UNIX operating systems have all functions described here.)

Note that very simple softwares such as

echo

doesn't have to care about multibyte character. and

wide characters. Such software can input and output multibyte character as is. Of course you

may modify these softwares using wide characters. It may be a good practice of wide character

programming. Examples of a fragment of source codes will be discussed in `Internal Processing

and File I/O' on page

75

.

There is an explanation of multibyte and wide characters also in Ken Lunde's  CJKV Information

Processing  (p25). However, the explanation is entirely wrong.

3

Some of you may know GNU libc uses UCS 4 for the internal expression of

wchar_t

. However, you should not

use the knowledge. It may differ in other systems.