xbd_chap01.html

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<p>The <i>c89</i> utility (which specified a compiler for the C Language specified by the ISO/IEC&nbsp;9899:1990 standard) has been
replaced by a <a href="../utilities/c99.html"><i>c99</i></a> utility (which specifies a compiler for the C Language specified by
the ISO/IEC&nbsp;9899:1999 standard).</p>

<p>From XSH5, text marked OH (Optional Header) has been reviewed on a case-by-case basis and removed where appropriate. The XCU5
text marked OF (Output Format Incompletely Specified) and UN (Possibly Unsupportable Feature) has been reviewed on a case-by-case
basis and removed where appropriate.</p>

<p>For the networking interfaces, the base document is the XNS, Issue 5.2 specification. The following parts of the XNS, Issue 5.2
specification are out of scope and not included in IEEE&nbsp;Std&nbsp;1003.1-2001:</p>

<ul>
<li>
<p>Part 3 (XTI)</p>
</li>

<li>
<p>Part 4 (Appendixes)</p>
</li>
</ul>

<p>Since there is much duplication between the XNS, Issue 5.2 specification and IEEE&nbsp;Std&nbsp;1003.1g-2000, material only from
the following sections of IEEE&nbsp;Std&nbsp;1003.1g-2000 has been included:</p>

<ul>
<li>
<p>General terms related to sockets (Section 2.2.2)</p>
</li>

<li>
<p>Socket concepts (Sections 5.1 through 5.3, inclusive)</p>
</li>

<li>
<p>The <a href="../functions/pselect.html"><i>pselect</i>()</a> function (Sections 6.2.2.1 and 6.2.3)</p>
</li>

<li>
<p>The <a href="../functions/sockatmark.html"><i>sockatmark</i>()</a> function (Section 5.4.13)</p>
</li>

<li>
<p>The <a href="../basedefs/sys/select.h.html"><i>&lt;sys/select.h&gt;</i></a> header (Section 6.2)</p>
</li>
</ul>

<p>Emphasis is placed on standardizing existing practice for existing users, with changes and additions limited to correcting
deficiencies in the following areas:</p>

<ul>
<li>
<p>Issues raised by IEEE or ISO/IEC Interpretations against IEEE Std 1003.1 and IEEE Std 1003.2</p>
</li>

<li>
<p>Issues raised in corrigenda for the Base Specifications and working group resolutions from The Open Group</p>
</li>

<li>
<p>Corrigenda and resolutions passed by The Open Group for the XNS, Issue 5.2 specification</p>
</li>

<li>
<p>Changes to make the text self-consistent with the additional material merged</p>
</li>

<li>
<p>A reorganization of the options in order to facilitate profiling, both for smaller profiles such as IEEE Std 1003.13, and larger
profiles such as the Single UNIX Specification</p>
</li>

<li>
<p>Alignment with the ISO/IEC&nbsp;9899:1999 standard</p>
</li>
</ul>

<h3><a name="tag_01_02">   1.2 </a>Conformance</h3>

<p>Conformance requirements for IEEE&nbsp;Std&nbsp;1003.1-2001 are defined in <a href=
"xbd_chap02.html#tag_02"><i>Conformance</i></a>.</p>

<h3><a name="tag_01_03">   1.3 </a>Normative References</h3>

<p>The following standards contain provisions which, through references in IEEE&nbsp;Std&nbsp;1003.1-2001, constitute provisions of
IEEE&nbsp;Std&nbsp;1003.1-2001. At the time of publication, the editions indicated were valid. All standards are subject to
revision, and parties to agreements based on IEEE&nbsp;Std&nbsp;1003.1-2001 are encouraged to investigate the possibility of
applying the most recent editions of the standards listed below. Members of IEC and ISO maintain registers of currently valid
International Standards.</p>

<dl compact>
<dt>ANS&nbsp;X3.9-1978</dt>

<dd>
(Reaffirmed 1989) American National Standard for Information Systems: Standard X3.9-1978, Programming Language FORTRAN.<a href=
"#tag_foot_1"><sup><small>1</small></sup></a></dd>

<dt>ISO/IEC&nbsp;646:1991</dt>

<dd>
ISO/IEC 646:1991, Information Processing - ISO 7-Bit Coded Character Set for Information Interchange.<a href=
"#tag_foot_2"><sup><small>2</small></sup></a></dd>

<dt>ISO&nbsp;4217:2001</dt>

<dd>
ISO 4217:2001, Codes for the Representation of Currencies and Funds.</dd>

<dt>ISO&nbsp;8601:2000</dt>

<dd>
ISO 8601:2000, Data Elements and Interchange Formats - Information Interchange - Representation of Dates and Times.</dd>

<dt>ISO C (1999)</dt>

<dd>
ISO/IEC 9899:1999, Programming Languages - C, including Technical Corrigendum 1.</dd>

<dt>ISO/IEC&nbsp;10646-1:2000</dt>

<dd>
ISO/IEC 10646-1:2000, Information Technology - Universal Multiple-Octet Coded Character Set (UCS) - Part 1: Architecture and Basic
Multilingual Plane.</dd>
</dl>

<h3><a name="tag_01_04">   1.4 </a>Terminology</h3>

<p>For the purposes of IEEE&nbsp;Std&nbsp;1003.1-2001, the following terminology definitions apply:</p>

<h4><a name="tag_01_04_01"></a>can</h4>

<p>Describes a permissible optional feature or behavior available to the user or application. The feature or behavior is mandatory
for an implementation that conforms to IEEE&nbsp;Std&nbsp;1003.1-2001. An application can rely on the existence of the feature or
behavior.</p>

<h4><a name="tag_01_04_02"></a>implementation-defined</h4>

<p>Describes a value or behavior that is not defined by IEEE&nbsp;Std&nbsp;1003.1-2001 but is selected by an implementor. The value
or behavior may vary among implementations that conform to IEEE&nbsp;Std&nbsp;1003.1-2001. An application should not rely on the
existence of the value or behavior. An application that relies on such a value or behavior cannot be assured to be portable across
conforming implementations.</p>

<p>The implementor shall document such a value or behavior so that it can be used correctly by an application.</p>

<h4><a name="tag_01_04_03"></a>legacy</h4>

<p>Describes a feature or behavior that is being retained for compatibility with older applications, but which has limitations
which make it inappropriate for developing portable applications. New applications should use alternative means of obtaining
equivalent functionality.</p>

<h4><a name="tag_01_04_04"></a>may</h4>

<p>Describes a feature or behavior that is optional for an implementation that conforms to IEEE&nbsp;Std&nbsp;1003.1-2001. An
application should not rely on the existence of the feature or behavior. An application that relies on such a feature or behavior
cannot be assured to be portable across conforming implementations.</p>

<p>To avoid ambiguity, the opposite of <i>may</i> is expressed as <i>need not</i>, instead of <i>may not</i>.</p>

<h4><a name="tag_01_04_05"></a>shall</h4>

<p>For an implementation that conforms to IEEE&nbsp;Std&nbsp;1003.1-2001, describes a feature or behavior that is mandatory. An
application can rely on the existence of the feature or behavior.</p>

<p>For an application or user, describes a behavior that is mandatory.</p>

<h4><a name="tag_01_04_06"></a>should</h4>

<p>For an implementation that conforms to IEEE&nbsp;Std&nbsp;1003.1-2001, describes a feature or behavior that is recommended but
not mandatory. An application should not rely on the existence of the feature or behavior. An application that relies on such a
feature or behavior cannot be assured to be portable across conforming implementations.</p>

<p>For an application, describes a feature or behavior that is recommended programming practice for optimum portability.</p>

<h4><a name="tag_01_04_07"></a>undefined</h4>

<p>Describes the nature of a value or behavior not defined by IEEE&nbsp;Std&nbsp;1003.1-2001 which results from use of an invalid
program construct or invalid data input.</p>

<p>The value or behavior may vary among implementations that conform to IEEE&nbsp;Std&nbsp;1003.1-2001. An application should not
rely on the existence or validity of the value or behavior. An application that relies on any particular value or behavior cannot
be assured to be portable across conforming implementations.</p>

<h4><a name="tag_01_04_08"></a>unspecified</h4>

<p>Describes the nature of a value or behavior not specified by IEEE&nbsp;Std&nbsp;1003.1-2001 which results from use of a valid
program construct or valid data input.</p>

<p>The value or behavior may vary among implementations that conform to IEEE&nbsp;Std&nbsp;1003.1-2001. An application should not
rely on the existence or validity of the value or behavior. An application that relies on any particular value or behavior cannot
be assured to be portable across conforming implementations.</p>

<h3><a name="tag_01_05">   1.5 </a>Portability</h3>

<p>Some of the utilities in the Shell and Utilities volume of IEEE&nbsp;Std&nbsp;1003.1-2001 and functions in the System Interfaces
volume of IEEE&nbsp;Std&nbsp;1003.1-2001 describe functionality that might not be fully portable to systems meeting the
requirements for POSIX conformance (see the Base Definitions volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href=
"../basedefs/xbd_chap02.html#tag_02">Chapter 2, Conformance</a>).</p>

<p>Where optional, enhanced, or reduced functionality is specified, the text is shaded and a code in the margin identifies the
nature of the option, extension, or warning (see <a href="#tag_01_05_01">Codes</a>). For maximum portability, an application
should avoid such functionality.</p>

<p>Unless the primary task of a utility is to produce textual material on its standard output, application developers should not
rely on the format or content of any such material that may be produced. Where the primary task <i>is</i> to provide such material,
but the output format is incompletely specified, the description is marked with the OF margin code and shading. Application
developers are warned not to expect that the output of such an interface on one system is any guide to its behavior on another
system.</p>

<h4><a name="tag_01_05_01">  1.5.1 </a>Codes</h4>

<p>The codes and their meanings are as follows. See also <a href="#tag_01_05_02">Margin Code Notation</a>.</p>

<p><sup>[<a href="javascript:open_code('ADV')">ADV</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
Advisory Information <img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
 The functionality described is optional. The functionality described is also an extension to the ISO&nbsp;C standard.</p>

<p>Where applicable, functions are marked with the ADV margin legend in the SYNOPSIS section. Where additional semantics apply to a
function, the material is identified by use of the ADV margin legend.</p>

<p><sup>[<a href="javascript:open_code('AIO')">AIO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
Asynchronous Input and Output <img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
 The functionality described is optional. The functionality described is also an extension to the ISO&nbsp;C standard.</p>

<p>Where applicable, functions are marked with the AIO margin legend in the SYNOPSIS section. Where additional semantics apply to a
function, the material is identified by use of the AIO margin legend.</p>

<p><sup>[<a href="javascript:open_code('BAR')">BAR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
Barriers <img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
 The functionality described is optional. The functionality described is also an extension to the ISO&nbsp;C standard.</p>

<p>Where applicable, functions are marked with the BAR margin legend in the SYNOPSIS section. Where additional semantics apply to a
function, the material is identified by use of the BAR margin legend.</p>

<p><sup>[<a href="javascript:open_code('BE')">BE</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
Batch Environment Services and Utilities <img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
 The functionality described is optional.</p>

<p>Where applicable, utilities are marked with the BE margin legend in the SYNOPSIS section. Where additional semantics apply to a
utility, the material is identified by use of the BE margin legend.</p>

<p><sup>[<a href="javascript:open_code('CD')">CD</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">