151 lines
5.0 KiB
HTML
151 lines
5.0 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>errno</title>
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<body bgcolor="white">
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<basefont size="3"> <a name="errno"></a> <a name="tag_03_129"></a><!-- errno -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_129_01"></a>NAME</h4>
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<blockquote>errno - error return value</blockquote>
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<h4><a name="tag_03_129_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <errno.h></tt></code></p>
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</blockquote>
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<h4><a name="tag_03_129_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The lvalue <i>errno</i> is used by many functions to return error values.</p>
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<p>Many functions provide an error number in <i>errno</i>, which has type <b>int</b> and is defined in <a href=
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"../basedefs/errno.h.html"><i><errno.h></i></a>. The value of <i>errno</i> shall be defined only after a call to a function
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for which it is explicitly stated to be set and until it is changed by the next function call or if the application assigns it a
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value. The value of <i>errno</i> should only be examined when it is indicated to be valid by a function's return value.
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Applications shall obtain the definition of <i>errno</i> by the inclusion of <a href=
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"../basedefs/errno.h.html"><i><errno.h></i></a>. No function in this volume of IEEE Std 1003.1-2001 shall set
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<i>errno</i> to 0.</p>
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<p>It is unspecified whether <i>errno</i> is a macro or an identifier declared with external linkage. If a macro definition is
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suppressed in order to access an actual object, or a program defines an identifier with the name <i>errno</i>, the behavior is
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undefined.</p>
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<p>The symbolic values stored in <i>errno</i> are documented in the ERRORS sections on all relevant pages.</p>
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</blockquote>
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<h4><a name="tag_03_129_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_129_05"></a>ERRORS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_129_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_129_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>Previously both POSIX and X/Open documents were more restrictive than the ISO C standard in that they required <i>errno</i>
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to be defined as an external variable, whereas the ISO C standard required only that <i>errno</i> be defined as a modifiable
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lvalue with type <b>int</b>.</p>
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<p>An application that needs to examine the value of <i>errno</i> to determine the error should set it to 0 before a function call,
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then inspect it before a subsequent function call.</p>
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</blockquote>
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<h4><a name="tag_03_129_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_129_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_129_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="xsh_chap02_03.html#tag_02_03"><i>Error Numbers</i></a> , the Base Definitions volume of IEEE Std 1003.1-2001,
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<a href="../basedefs/errno.h.html"><i><errno.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_129_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_129_12"></a>Issue 5</h4>
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<blockquote>
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<p>The following sentence is deleted from the DESCRIPTION: "The value of <i>errno</i> is 0 at program start-up, but is never set
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to 0 by any XSI function". The DESCRIPTION also no longer states that conforming implementations may support the declaration:</p>
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<pre>
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<tt>extern int errno;
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_129_13"></a>Issue 6</h4>
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<blockquote>
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<p>Obsolescent text regarding defining <i>errno</i> as:</p>
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<pre>
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<tt>extern int errno
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</tt>
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</pre>
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<p>is removed.</p>
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<p>Text regarding no function setting <i>errno</i> to zero to indicate an error is changed to no function shall set <i>errno</i> to
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zero. This is for alignment with the ISO/IEC 9899:1999 standard.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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