charset.html

unix 下的C开发手册,还用详细的例程。

C Language Wide-character Codes
</a></xref>).
The wide-character value for each member of the
Portable Character Set will equal its
value when used as the lone character in an
integer character constant.
Wide-character codes for other characters
are locale- and implementation-dependent.
State shift bytes do not have a wide-character code representation.
<h3><a name = "tag_001_004">&nbsp;</a>Character Set Description File</h3>
<xref type="2" name="charmap"></xref>
Implementations provide a character set
description file for at least one coded character set
supported by the implementation.
These files are referred
to elsewhere in this specification set as
<i>charmap</i>
files.
It is implementation-dependent whether or not users or applications can
provide additional character set description files.
<p>
This specification set does not require that multiple character sets
or codesets be supported.
Although multiple charmap
files are supported, it is the responsibility of the implementation
to provide the file or files;
if only one is provided, only that one will be accessible using the
<i><a href="../xcu/localedef.html">localedef</a></i>
utility's
<b>-f</b>
option (although in the case of just one file on the system,
<b>-f</b>
is not useful).
<p>
Each character set description file defines
characteristics for the coded character set and
the encoding for the characters
specified in
<xref href=portchar><a href="#tagt_1">
Portable Character Set
</a></xref>
and may define encoding for additional
characters supported by the implementation.
Other information about the coded character set may also be in the file.
Coded character set character values are defined
using symbolic character names followed by character encoding values.
<p>
The character set description file provides:
<ul>
<p>
<li>
The capability to describe character set attributes (such as collation
order or character classes) independent of character set encoding, and
using only the characters in the portable character set.
This makes it
possible to create generic
<i><a href="../xcu/localedef.html">localedef</a></i>
source files for all codesets that share the portable character set
(such as the ISO 8859 family or IBM Extended ASCII).
<p>
<li>
Standardised symbolic names for all characters in the portable character
set, making it possible to refer to any such character
regardless of encoding.
<p>
</ul>
<p>
The charmap file was introduced to resolve problems with the
portability of, especially,
<i><a href="../xcu/localedef.html">localedef</a></i>
sources.
This specification set assumes that the portable character set is constant
across all locales, but does not prohibit implementations from supporting
two incompatible codings, such as
both ASCII and EBCDIC.
Such dual-support implementations
should have all charmaps and
<i><a href="../xcu/localedef.html">localedef</a></i>
sources encoded using one
portable character set, in effect cross-compiling for the other
environment.
Naturally, charmaps (and
<i><a href="../xcu/localedef.html">localedef</a></i>
sources) are
only portable without transformation between systems using the same
encodings for the portable character set.
They can, however, be transformed
between two sets using only a subset of the actual characters
(the portable set).
However, the particular coded
character set used for an application or an implementation
does not necessarily imply different characteristics or collation;
on the contrary, these attributes should in many
cases be identical, regardless of codeset.
The charmap provides the capability to define a common
locale definition for multiple codesets (the same
<i><a href="../xcu/localedef.html">localedef</a></i>
source can be used for codesets with different extended
characters;
the ability in the charmap to define empty
names allows for characters missing in certain codesets).
<p>
Each symbolic name specified in
<xref href=portchar><a href="#tagt_1">
Portable Character Set
</a></xref>
is included in
the file and is mapped to a unique encoding value
(except for those symbolic names that are shown
with identical glyphs).
If the control characters commonly associated with
the symbolic names in the following table
are supported by
the implementation, the symbolic names and their
corresponding encoding values are included in the file.
Some of the
encodings associated with the
symbolic names in this table may be
the same as characters in
the portable character set table.
<pre>
<center>
<table  bordercolor=#000000 border=1 align=center>
<tr valign=top><td align=center>&lt;ACK&gt;
<td align=center>&lt;DC2&gt;
<td align=center>&lt;ENQ&gt;
<td align=center>&lt;FS&gt;
<td align=center>&lt;IS4&gt;
<td align=center>&lt;SOH&gt;
<tr valign=top><td align=center>&lt;BEL&gt;
<td align=center>&lt;DC3&gt;
<td align=center>&lt;EOT&gt;
<td align=center>&lt;GS&gt;
<td align=center>&lt;LF&gt;
<td align=center>&lt;STX&gt;
<tr valign=top><td align=center>&lt;BS&gt;
<td align=center>&lt;DC4&gt;
<td align=center>&lt;ESC&gt;
<td align=center>&lt;HT&gt;
<td align=center>&lt;NAK&gt;
<td align=center>&lt;SUB&gt;
<tr valign=top><td align=center>&lt;CAN&gt;
<td align=center>&lt;DEL&gt;
<td align=center>&lt;ETB&gt;
<td align=center>&lt;IS1&gt;
<td align=center>&lt;RS&gt;
<td align=center>&lt;SYN&gt;
<tr valign=top><td align=center>&lt;CR&gt;
<td align=center>&lt;DLE&gt;
<td align=center>&lt;ETX&gt;
<td align=center>&lt;IS2&gt;
<td align=center>&lt;SI&gt;
<td align=center>&lt;US&gt;
<tr valign=top><td align=center>&lt;DC1&gt;
<td align=center>&lt;EM&gt;
<td align=center>&lt;FF&gt;
<td align=center>&lt;IS3&gt;
<td align=center>&lt;SO&gt;
<td align=center>&lt;VT&gt;
</table>
<h6 align=center><xref table="Control Character Set"><a name="tagt_2">&nbsp;</a></xref>Table: Control Character Set</h6>
<xref type="7" name="cntlchar"></xref>
</center>
</pre>
<p>
The following declarations can precede the character definitions.
Each must consist of the symbol shown in the following list,
starting in column 1,
including the surrounding brackets, followed by one or more
blank characters,
followed by the value to be assigned to the symbol.
<dl compact>

<dt><b>&lt;code_set_name&gt;</b><dd>The name of the coded character set for which
the character set description file is defined.
The characters of the name must be taken from the
set of characters
with visible glyphs defined in
<xref href=portchar><a href="#tagt_1">
Portable Character Set
</a></xref>.

<dt><b>&lt;mb_cur_max&gt;</b><dd>The maximum number of bytes in a multi-byte character.
This defaults to 1.

<dt><b>&lt;mb_cur_min&gt;</b><dd>An unsigned positive integer value that
defines the minimum number of bytes in a
character for the encoded character set.
On XSI-conformant systems,
<b>&lt;mb_cur_min&gt;</b>
is always 1.

<dt><b>&lt;escape_char&gt;</b><dd>The escape character used to indicate that the
characters following will be interpreted in a
special way, as defined later in this section.
This defaults to backslash
(\),
which is the character glyph used in all the following text and examples,
unless otherwise noted.

<dt><b>&lt;comment_char&gt;</b><dd>The character that when placed in column 1 of a
charmap
line, is used to indicate that the line is to be ignored.
The default character is the number sign (#).

</dl>
<p>
The character set mapping definitions will be all the lines
immediately following an identifier line containing the string
<b>CHARMAP</b>
starting in column 1, and preceding a trailer
line containing the string
<b>END</b>CHARMAP
starting in column 1.
Empty lines and lines containing a
<b>&lt;comment_char&gt;</b>
in the first column will be ignored.
Each non-comment line of the character set mapping
definition (that is, between the
<b>CHARMAP</b>
and
<b>END</b>CHARMAP
lines of the file) must be in either of two forms:
<p>
<dl compact><dt> <dd>
<p>
<tt>"%s %s %s\n"</tt>, &lt;<i>symbolic-name</i>&gt;,
&lt;<i>encoding</i>&gt;,
&lt;<i>comments</i>&gt;
</p>
</dl>
</p>
or:
<p>
<dl compact><dt> <dd>
<p>
<tt>"%s...%s %s %s\n"</tt>, &lt;<i>symbolic-name</i>&gt;,
&lt;<i>symbolic-name</i>&gt;,
&lt;<i>encoding</i>&gt;,
&lt;<i>comments</i>&gt;
</p>
</dl>
</p>
<p>
In the first format, the line in the character set mapping definition
defines a single symbolic name and a corresponding encoding.
A symbolic name is one or more characters from the set shown
with visible glyphs in
<xref href=portchar><a href="#tagt_1">
Portable Character Set
</a></xref>,
enclosed between angle brackets.
A character following an escape character is interpreted as itself;
for example, the sequence
&lt;\\\&gt;&gt;
represents the symbolic name
\&gt;
enclosed between angle brackets.
<p>
In the second format, the line in the character set mapping definition
defines a range of one or more symbolic names.
In this form, the symbolic
names must consist of zero or more non-numeric characters from the set
shown with visible glyphs in
<xref href=portchar><a href="#tagt_1">
Portable Character Set
</a></xref>,
followed by an integer formed by one or more decimal digits.
The characters preceding the integer
must be
identical in the two symbolic names, and the integer formed by the digits
in the second symbolic name must be equal to or greater than the integer
formed by the digits in the first name.
This is interpreted
as a series of symbolic names formed from the common part and each of
the integers between the first and the second integer, inclusive.
As an example,
&lt;j0101&gt;...&lt;j0104&gt;
is interpreted as the symbolic names
&lt;j0101&gt;,
&lt;j0102&gt;,
&lt;j0103&gt;
and
&lt;j0104&gt;,
in that order.
<p>
A character set mapping definition line must exist for all symbolic
names specified in
<xref href=portchar><a href="#tagt_1">
Portable Character Set
</a></xref>,
and must define the coded character value
that corresponds to the character glyph indicated in the table, or
the coded character value that corresponds with the control character
symbolic name.
If the control characters commonly associated with the
symbolic names in 
<xref href=cntlchar><a href="#tagt_2">
Control Character Set
</a></xref>
are supported by the implementation,
the symbolic name and the corresponding encoding value must be included
in the file.
Additional unique symbolic names may be included.
A coded character value can be represented by more than one symbolic name.
<p>
The encoding part is expressed as one (for single-byte character
values) or more concatenated decimal, octal or hexadecimal
constants in the following formats:
<p>
<dl compact><dt> <dd>
<tt>"%cd%d"</tt>, &lt;<i>escape_char</i>&gt;,
&lt;<i>decimal&nbsp;byte&nbsp;value</i>&gt;
</dl>
</p>
<p>
<dl compact><dt> <dd>
<tt>"%cx%x"</tt>, &lt;<i>escape_char</i>&gt;,
&lt;<i>hexadecimal&nbsp;byte&nbsp;value</i>&gt;
</dl>
</p>
<p>
<dl compact><dt> <dd>
<tt>"%c%o"</tt>, &lt;<i>escape_char</i>&gt;,
&lt;<i>octal&nbsp;byte&nbsp;value</i>&gt;
</dl>
</p>
<p>
Decimal constants must be represented by two or three decimal
digits, preceded by the escape character and the lower-case letter
d;
for example,
\d05,
\d97
or
\d143.
Hexadecimal constants must be represented by
two hexadecimal digits, preceded by the escape
character and the lower-case letter
x;
for example,
\x05,
\x61
or
\x8f.
Octal constants must be represented by two or three octal
digits, preceded by the escape character; for example,
\05,
\141
or
\217.
In a portable charmap file, each constant must represent an 8-bit byte.
Implementations supporting other
byte sizes may allow constants to represent values larger than those
that can be represented in 8-bit bytes, and to allow additional
digits in constants.
When constants are concatenated for multi-byte character values,
they must be of the same type, and
interpreted in byte order from
first to last with the least significant byte of the multi-byte character
specified by the last constant.
The manner in which these
constants are represented in the character
stored in the system is implementation-dependent.
(This big endian notation was chosen for reasons of portability.
There is no requirement that the internal representation
in the computer memory be in this same order.)
Omitting bytes from a multi-byte character definition
produces undefined results.
<p>
In lines defining ranges of symbolic names, the encoded value is the
value for the first symbolic name in the range (the symbolic name
preceding the ellipsis).
Subsequent symbolic names defined by the range
will have encoding values in increasing order.
For example, the line:
<code>
<pre>
&lt;j0101&gt;...&lt;j0104&gt;    \d129\d254
</code>
</pre>
<p>
will be interpreted as:
<code>
<pre>
&lt;j0101&gt;              \d129\d254
&lt;j0102&gt;              \d129\d255
&lt;j0103&gt;              \d130\d0
&lt;j0104&gt;              \d130\d1
</code>
</pre>
<p>
Note that this line will be interpreted as the example even on
systems with bytes larger than 8 bits.
<p>
The comment is optional.
<p>
For the interpretation of the dollar sign and the number sign, see
<xref href=dollarsign><a href="glossary.html#tag_004_000_079">
dollar sign
</a></xref>
and
<xref href=numbersign><a href="glossary.html#tag_004_000_180">
number sign
</a></xref>.

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