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<H2><A NAME="Trigraphs">Trigraphs</A></H2>

<P>A <B>trigraph</B> is a sequence of three characters that begins
with two question marks (<CODE>??</CODE>). You use trigraphs to write C
source files with a character set that does not contain convenient
graphic representations for some punctuation characters. (The resultant
C source file is not necessarily more readable, but it is unambiguous.)</P>

<P>The list of all
<B><A NAME="defined trigraphs">defined trigraphs</A></B> is:</P>

<PRE><B>Character</B>   <B>Trigraph</B>
[           ??(
\           ??/
]           ??)
^           ??'
{           ??&lt;
|           ??!
}           ??&gt;
~           ??-
#           ??=</PRE>

<P>These are the only trigraphs. The translator does not alter any other
sequence that begins with two question marks.</P>

<P>For example, the expression statements:</P>

<PRE>    printf("Case ??=3 is done??/n");
    printf("You said what????/n");</PRE>

<P>are equivalent to:</P>

<PRE>    printf("Case #3 is done\n");
    printf("You said what??\n");</PRE>

<P>The translator replaces each trigraph with its equivalent single
character representation in an early
<A HREF="preproc.html#Phases of Translation">phase of translation</A>.
You can always treat a trigraph as a single source character.</P>

<H2><A NAME="Multibyte Characters">Multibyte Characters</A></H2>

<P>A source character set or target character set can also contain
<B>multibyte characters</B> (sequences of one or more bytes). Each
sequence represents a single character in the
<B><A NAME="extended character set">extended character set</A></B>.
You use multibyte characters to represent large sets of characters,
such as Kanji. A multibyte character can be a one-byte sequence that
is a character from the
<A HREF="#basic C character set">basic C character set</A>,
an additional one-byte sequence that is implementation defined,
or an additional sequence of two or more bytes that is
implementation defined.</P>

<P>Any multibyte encoding that contains sequences of two or more
bytes depends, for its interpretation between bytes, on a
<B><A NAME="conversion state">conversion state</A></B> determined
by bytes earlier in the sequence of characters. In the
<B><A NAME="initial conversion state">initial conversion state</A></B>
if the byte immediately following matches one of the characters
in the basic C character set, the byte must represent that character.</P>

<P>For example, the
<B><A NAME="EUC encoding">EUC encoding</A></B> is a superset of ASCII.
A byte value in the interval [0xA1, 0xFE] is the first of a two-byte
sequence (whose second byte value is in the interval [0x80, 0xFF]).
All other byte values are one-byte sequences. Since all members of the
<A HREF="#basic C character set">basic C character set</A>
have byte values in the range [0x00, 0x7F] in ASCII,
EUC meets the requirements
for a multibyte encoding in Standard C. Such a sequence is <I>not</I>
in the initial conversion state immediately after a byte value in
the interval [0xA1, 0xFe]. It is ill-formed if a second byte
value is not in the interval [0x80, 0xFF].

<P>Multibyte characters can also have a
<B><A NAME="state-dependent encoding">state-dependent encoding</A></B>.
How you interpret a byte in such an encoding depends on a
conversion state that involves both a
<B><A NAME="parse state">parse state</A></B>, as before, and a
<B><A NAME="shift state">shift state</A></B>, determined
by bytes earlier in the sequence of characters. The
<B><A NAME="initial shift state">initial shift state</A></B>,
at the beginning of a new multibyte character, is also the
initial conversion state. A subsequent
<B><A NAME="shift sequence">shift sequence</A></B> can determine an
<B><A NAME="alternate shift state">alternate shift state</A></B>,
after which all byte sequences (including one-byte sequences) can have
a different interpretation. A byte containing the value zero,
however, always represents the
<A HREF="#null character">null character</A>.
It cannot occur as any of the bytes of another multibyte character.</P>

<P>For example, the
<B><A NAME="JIS encoding">JIS encoding</A></B> is another superset of ASCII.
In the initial shift state, each byte represents a single character,
except for two three-byte shift sequences:</P>

<UL>
<LI>The three-byte sequence <CODE>"\x1B$B"</CODE> shifts to two-byte mode.
Subsequently, two successive bytes (both with values
in the range [0x21, 0x7E]) constitute a single multibyte character.</LI>

<LI>The three-byte sequence <CODE>"\x1B(B"</CODE> shifts back
to the initial shift state.</LI>
</UL>

<P>JIS also meets the requirements for a multibyte encoding in Standard C.
Such a sequence is <I>not</I> in the initial conversion state
when partway through a three-byte shift sequence
or when in two-byte mode.</P>

<P>(<A HREF="lib_over.html#Amendment 1">Amendment 1</A> adds the type
<A HREF="wchar.html#mbstate_t"><CODE>mbstate_t</CODE></A>,
which describes an object that can store a conversion state.
It also relaxes the above rules for
<A HREF="lib_file.html#generalized multibyte characters">
generalized multibyte characters</A>, which describe the encoding
rules for a broad range of
<A HREF="lib_file.html#wide stream">wide streams</A>.)</P>

<P>You can write multibyte characters in C source text as part
of a comment, a character constant, a string literal, or a filename in an
<A HREF="preproc.html#include directive"><I>include</I> directive</A>.
How such characters print is implementation
defined. Each sequence of multibyte characters that you write must
begin and end in the initial shift state.
The program can also include multibyte characters in
<A HREF="#null-terminated string">null-terminated</A>
<A HREF="lib_over.html#C string">C strings</A>
used by several library functions, including the
<A HREF="lib_prin.html#format string">format strings</A> for
<A HREF="stdio.html#printf"><CODE>printf</CODE></A> and
<A HREF="stdio.html#scanf"><CODE>scanf</CODE></A>.
Each such character string must begin and end
in the initial shift state.</P>

<H3><A NAME="Wide-Character Encoding">
Wide-Character Encoding</A></H3>

<P>Each character in the extended character set also has an integer
representation, called a <B>wide-character encoding</B>.
Each extended character has a unique wide-character value.
The value zero always corresponds to the
<B><A NAME="null wide character">null wide character</A></B>.
The type definition
<A HREF="stddef.html#wchar_t"><CODE>wchar_t</CODE></A>
specifies the integer type that represents wide characters.</P>

<P>You write a
<B><A NAME="wide-character constant">wide-character constant</A></B>
as <CODE>L'mbc'</CODE>, where <CODE>mbc</CODE> represents
a single multibyte character.
You write a
<B><A NAME="wide-character string literal">
wide-character string literal</A></B> as <CODE>L"mbs"</CODE>,
where <CODE>mbs</CODE> represents
a sequence of zero or more multibyte characters.
The wide-character string literal
<CODE>L"xyz"</CODE> becomes a sequence of
wide-character constants stored in successive bytes of memory, followed
by a null wide character:<BR>
<CODE>{L'x', L'y', L'z', L'\0'}</CODE>

<P>The following library functions
help you convert between the multibyte
and wide-character representations of extended characters:
<A HREF="wchar.html#btowc"><CODE>btowc</CODE></A>,
<A HREF="stdlib.html#mblen"><CODE>mblen</CODE></A>,
<A HREF="wchar.html#mbrlen"><CODE>mbrlen</CODE></A>,
<A HREF="wchar.html#mbrtowc"><CODE>mbrtowc</CODE></A>,
<A HREF="wchar.html#mbsrtowcs"><CODE>mbsrtowcs</CODE></A>,
<A HREF="stdlib.html#mbstowcs"><CODE>mbstowcs</CODE></A>,
<A HREF="stdlib.html#mbtowc"><CODE>mbtowc</CODE></A>,
<A HREF="wchar.html#wcrtomb"><CODE>wcrtomb</CODE></A>,
<A HREF="wchar.html#wcsrtombs"><CODE>wcsrtombs</CODE></A>,
<A HREF="stdlib.html#wcstombs"><CODE>wcstombs</CODE></A>,
<A HREF="wchar.html#wctob"><CODE>wctob</CODE></A>, and
<A HREF="stdlib.html#wctomb"><CODE>wctomb</CODE></A>.
</P>

<P>The macro
<A HREF="limits.html#MB_LEN_MAX"><CODE>MB_LEN_MAX</CODE></A>
specifies the length of the longest possible multibyte sequence required
to represent a single character defined by the implementation across
supported locales. And the macro
<A HREF="stdlib.html#MB_CUR_MAX"><CODE>MB_CUR_MAX</CODE></A>
specifies the length of the longest possible multibyte sequence required
to represent a single character defined for the current
<A HREF="locale.html#locale">locale</A>.</P>

<P>For example, the
<A HREF="#string literal">string literal</A>
<CODE>"hello"</CODE> becomes an array of six <I>char:</I></P>

<PRE>    {'h', 'e', 'l', 'l', 'o', 0}</PRE>

<P>while the wide-character string literal
<CODE>L"hello"</CODE> becomes
an array of six integers of type
<A HREF="stddef.html#wchar_t"><CODE>wchar_t</CODE></A>:</P>

<PRE>    {L'h', L'e', L'l', L'l', L'o', 0}</PRE>

<HR>
<P>See also the
<B><A HREF="index.html#Table of Contents">Table of Contents</A></B> and the
<B><A HREF="_index.html">Index</A></B>.</P>

<P><I>
<A HREF="crit_pb.html">Copyright</A> &#169; 1989-2002
by P.J. Plauger and Jim Brodie. All rights reserved.</I></P>

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