glossary.html

unix 下的C开发手册,还用详细的例程。

in some international standards, where it is used as a synonym for
<i>octet</i>
(always eight bits).
On a system based on the ISO/IEC 9945-2:1993 standard, a byte may be larger than eight bits
so that it can be an integral portion of larger data objects
that are not evenly divisible by eight bits (such as a
36-bit word that contains four 9-bit bytes).
<p>
<h4><a name = "tag_004_000_041">&nbsp;</a>carriage-return character</h4>A character
that in the output stream indicates that
printing should start at the beginning
of the same physical line in which the
carriage-return character occurred.
The carriage-return
is the character designated by
'\r'
in the C language.
It is unspecified whether
this character is the exact sequence transmitted to an output device by
the system to accomplish the movement to the beginning of the line.
<p>
<h4><a name = "tag_004_000_042">&nbsp;</a>character</h4><xref type="11" name="character"></xref>
A sequence of one or more bytes representing a single
graphic symbol or control code.
This term corresponds to the ISO&nbsp;C standard term
<i>multibyte character</i> (multi-byte character),
where a single-byte character is a special case of a
multi-byte character.
Unlike the usage in the ISO&nbsp;C standard,
<i>character</i>
here has no necessary relationship with storage space, and
<i>byte</i>
is used when storage space is discussed.
<p>
See
<xref href=charset><a href="charset.html#tag_001_001">
Portable Character Set
</a></xref>
for a further explanation of the graphical
representations of characters, or <i>glyphs</i>,
as opposed to character encodings.
<p>
<h4><a name = "tag_004_000_043">&nbsp;</a>character array</h4>An array of type
<b>char</b>.
<p>
<h4><a name = "tag_004_000_044">&nbsp;</a>character class</h4>A named set of characters
sharing an attribute associated
with the name of the class.
The classes and the characters
that they contain are dependent on the value of the
LC_CTYPE category in the current locale;
see
<xref href=lc_ctype><a href="locale.html#tag_005_003_001">
LC_CTYPE
</a></xref>.
<p>
<h4><a name = "tag_004_000_045">&nbsp;</a>character set</h4>A finite set of different characters used for the representation,
organisation or control of data.
<p>
<h4><a name = "tag_004_000_046">&nbsp;</a>character special file</h4>A file that refers to a device.
One specific type of character special file is a terminal device file,
whose access is defined in
<xref href=genterm><a href="termios.html#tag_008">
General Terminal Interface
</a></xref>.
<p>
<h4><a name = "tag_004_000_047">&nbsp;</a>character string</h4>A contiguous sequence of characters terminated by and including
the first null byte.
<p>
<h4><a name = "tag_004_000_048">&nbsp;</a>child process</h4>See
<xref href=processdef><a href="#tag_004_000_216">
process
</a></xref>.
<p>
<h4><a name = "tag_004_000_049">&nbsp;</a>circumflex</h4>The character "^".
<p>
<h4><a name = "tag_004_000_050">&nbsp;</a>clock</h4>An object that measures the passage of time.
<p>
The current value of the time measured by a
clock can be queried and, possibly,
set to a value within the legal range of the clock.
<p>
<h4><a name = "tag_004_000_051">&nbsp;</a>clock tick</h4>An interval of time; an implementation-dependent number of these
occur each second.
<p>
<h4><a name = "tag_004_000_052">&nbsp;</a>coded character set</h4>A set of unambiguous rules that establishes a character set
and the one-to-one relationship between each character of the set
and its bit representation.
<p>
<h4><a name = "tag_004_000_053">&nbsp;</a>codeset</h4>The result of applying rules that map a numeric code value to each element of
a character set.  An element of a character set may be related to more than
one numeric code value but the reverse is not true.  However, for
state-dependent encodings the relationship between numeric code values to
elements of a character set may be further
controlled by state information; see
<xref href=char_enc><a href="charset.html#tag_001_002">
Character Encoding
</a></xref>.
The character set may contain fewer elements than the total number of
possible numeric code values; that is, some code values may be unassigned.
<p>
<h4><a name = "tag_004_000_054">&nbsp;</a>collating element</h4>The smallest entity used to determine the logical ordering of
character or wide-character strings.
See
<xref href=collseq><a href="#tag_004_000_056">
collation sequence
</a></xref>.
A collating element consists of either
a single character, or two or
more characters collating as a single entity.
The value of the LC_COLLATE
category in the current locale determines
the current set of collating elements.
<p>
<h4><a name = "tag_004_000_055">&nbsp;</a>collation</h4>The logical ordering of
character or wide-character strings
according to defined precedence rules.
These rules identify a collation sequence
between the collating elements,
and such additional rules that can be used to order strings
consisting of multiple collating elements.
<p>
<h4><a name = "tag_004_000_056">&nbsp;</a>collation sequence</h4><xref type="11" name="collseq"></xref>
The relative order of collating elements
as determined by the setting of the
LC_COLLATE category in the current locale.
The character order, as defined for the LC_COLLATE category
in the current locale,
defines the relative order
of all collating elements, such that each element occupies
a unique position in the order.
This is the order used in ranges of characters and
collating elements in regular expressions and pattern matching.
In addition, the definition of the collating
weights of characters and collating elements
uses collating elements to represent their
respective positions within the collation sequence.
<p>
Multi-level sorting is accomplished by assigning elements one or more
collation weights, up to the limit
{COLL_WEIGHTS_MAX};
see
<i><a href="../xsh/limits.h.html">&lt;limits.h&gt;</a></i>.
On each level,
elements may be given the same weight
(at the primary level, called an
equivalence class; see
<xref href=equivclass><a href="#tag_004_000_094">
equivalence class
</a></xref>)
or be omitted from the sequence.
Strings that collate equal using the
first assigned weight (primary ordering) are then compared using
the next assigned weight (secondary ordering), and so on.
<p>
<h4><a name = "tag_004_000_057">&nbsp;</a>column position</h4><xref type="11" name="colpos"></xref>
A unit of horizontal measure related to characters in a line.
<p>
It is assumed that each character in a character set has an intrinsic
column width independent of any output device.
Each printable character in
the portable character set has a column width of one.
The standard utilities, when used as described in this specification set,
assume that all characters have integral column widths.
The column width of a character
is not necessarily related to the internal representation
of the character (numbers of bits or
bytes).
<p>
The column position of a character in a line is defined as one plus
the sum of the column widths of the preceding characters in the line.
Column positions are numbered starting from 1.
<p>
<h4><a name = "tag_004_000_058">&nbsp;</a>command</h4>A directive to the shell to perform a particular task;
see
the <b>XCU</b> specification, <a href="../xcu/chap2.html#tag_001_009"><b>Shell Commands</b>&nbsp;</a>.
<p>
<h4><a name = "tag_004_000_059">&nbsp;</a>command language interpreter</h4>An interface that interprets sequences of text input as commands.
It may operate on an input stream
or it may interactively prompt and read commands from a terminal.
It is possible for applications to invoke utilities through a number of
interfaces, which are collectively considered to act as command interpreters.
The most obvious of these are the
<i><a href="../xcu/sh.html">sh</a></i>
utility and the
<i><a href="../xsh/system.html">system()</a></i>
function, although
<i><a href="../xsh/popen.html">popen()</a></i>
and the various forms of
<i>exec</i>
may also be considered to behave as interpreters.
<p>
<h4><a name = "tag_004_000_060">&nbsp;</a>composite graphic symbol</h4>A graphic symbol consisting of a combination of two or more
other graphic symbols in a single character position,
such as a diacritical mark and a basic letter.
<p>
<h4><a name = "tag_004_000_061">&nbsp;</a>condition variable</h4>A synchronization object which
allows a thread to suspend execution, repeatedly,
until some associated predicate becomes true.
<p>
<h4><a name = "tag_004_000_062">&nbsp;</a>control character</h4>A character, other than a graphic character,
that affects the recording,
processing, transmission or interpretation of text.
<br>
<p>
<h4><a name = "tag_004_000_063">&nbsp;</a>control operator</h4>In the shell,
a token that performs a control function.
It is one of the following symbols:
<code>
<pre>
&amp;   &amp;&amp;   (   )   ;   ;;   newline   |   ||
</code>
</pre>
<p>
The end-of-input indicator used internally by the shell
is also considered a control operator.
See
the <b>XCU</b> specification, <a href="../xcu/chap2.html#tag_001_003"><b>Token Recognition</b>&nbsp;</a>.
<p>
On some systems, the symbol
<b>((</b>
is a control operator;
its use produces unspecified results.
Applications that wish to have nested subshells, such as:
<code>
<pre>
((echo Hello);(echo World))
</code>
</pre>
must separate the
<b>((</b>
characters into two tokens by including white space between them.
Some systems may treat these as invalid arithmetic expressions
instead of subshells.
<p>
The
<b>((</b>
and
<b>))</b>
symbols are control operators in the KornShell,
used for an alternative syntax of an arithmetic expression command.
A portable application cannot use
<b>((</b>
as a single token
(with the exception of the
<b>$((</b>
form for shell arithmetic).
<p>
<h4><a name = "tag_004_000_064">&nbsp;</a>controlling process</h4>The session leader that established the connection to the
controlling terminal.
If the terminal ceases to be a controlling terminal for this session,
the session leader ceases to be the controlling process.
<p>
<h4><a name = "tag_004_000_065">&nbsp;</a>controlling terminal</h4>A terminal that is associated with a session.
Each session may have at most one controlling terminal associated with it,
and a controlling terminal is associated with exactly one session.
Certain input sequences from the controlling terminal (see
<xref href=genterm><a href="termios.html#tag_008">
General Terminal Interface
</a></xref>)
cause signals to be sent to all processes in the process group
associated with the controlling terminal.
<p>
<h4><a name = "tag_004_000_066">&nbsp;</a>conversion descriptor</h4>A per-process unique value
used to identify an open codeset conversion.
<p>
<h4><a name = "tag_004_000_067">&nbsp;</a>core file</h4>A file of unspecified format that may be generated when a process terminates
abnormally.
<p>
<h4><a name = "tag_004_000_068">&nbsp;</a>current working directory</h4>See
<xref href=workdir><a href="#tag_004_000_328">
working directory
</a></xref>.
<p>
<h4><a name = "tag_004_000_069">&nbsp;</a>cursor position</h4>The line and column position on the screen denoted by the terminal's cursor.
<p>
<h4><a name = "tag_004_000_070">&nbsp;</a>data segment</h4>Memory associated with a process, that may be used to contain dynamically
allocated data.
<p>
<h4><a name = "tag_004_000_071">&nbsp;</a>device</h4>A computer peripheral or an object that appears to the application as such.
<p>
<h4><a name = "tag_004_000_072">&nbsp;</a>device ID</h4>A non-negative integer used to identify a device.
<p>
<h4><a name = "tag_004_000_073">&nbsp;</a>direct I/O</h4>An operation that attempts to circumvent a system performance
optimization for the optimization of the individual I/O operation.
<p>
<h4><a name = "tag_004_000_074">&nbsp;</a>directory</h4>A file that contains directory entries.
No two directory entries in the same directory have the same name.
<p>
<h4><a name = "tag_004_000_075">&nbsp;</a>directory entry</h4><xref type="11" name="direntry"></xref>
(Or <b>link</b>.)
An object that associates a filename with a file.
Several directory entries can associate names with the same file.
<p>
<h4><a name = "tag_004_000_076">&nbsp;</a>directory stream</h4>A sequence of all the directory entries in a particular directory.
An open directory stream
may be implemented using a file descriptor.
<p>
<h4><a name = "tag_004_000_077">&nbsp;</a>disarm (a timer)</h4>To stop a timer from measuring the passage of time,
disabling any future process notifications (until the timer is armed 
again).
<p>
<h4><a name = "tag_004_000_078">&nbsp;</a>display</h4><xref type="11" name="display"></xref>
To output to the user's terminal.
If the output is not directed to a terminal,
the results are undefined.
<p>
The <b>XCU</b> specification assigns precise requirements for the terms
<i>display</i>
and
<i>write</i>.
Some historical systems have chosen to implement
certain utilities without using the traditional
UNIX system file descriptor model.
For example, the
<i><a href="../xcu/vi.html">vi</a></i>
editor might employ direct screen memory updates
on a personal computer, rather than a
<i><a href="../xsh/write.html">write()</a></i>
system call.
An instance of user prompting might appear in
a dialogue box, rather than with standard error.
When the <b>XCU</b> specification uses the term
<i>display,</i>
the method of outputting to the terminal is unspecified; many
historical implementations use
<i>termcap</i>
or
<i>terminfo</i>,
but this is not a requirement.
The term
<i>write</i>
is used when the <b>XCU</b> specification mandates that
a file descriptor be used and that the output can be redirected.