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126 lines
5.4 KiB
HTML
126 lines
5.4 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>signal (The Red Hat newlib C Library)</title>
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<meta name="description" content="signal (The Red Hat newlib C Library)">
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<meta name="keywords" content="signal (The Red Hat newlib C Library)">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Document-Index.html#Document-Index" rel="index" title="Document Index">
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<link href="Document-Index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Signals.html#Signals" rel="up" title="Signals">
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<link href="Timefns.html#Timefns" rel="next" title="Timefns">
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</head>
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<body lang="en">
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<a name="signal"></a>
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<div class="header">
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<p>
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Previous: <a href="raise.html#raise" accesskey="p" rel="prev">raise</a>, Up: <a href="Signals.html#Signals" accesskey="u" rel="up">Signals</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="signal_002d_002d_002dspecify-handler-subroutine-for-a-signal"></a>
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<h3 class="section">7.3 <code>signal</code>—specify handler subroutine for a signal</h3>
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<a name="index-signal"></a>
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<a name="index-_005fsignal_005fr"></a>
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<p><strong>Synopsis</strong>
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</p><div class="example">
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<pre class="example">#include <signal.h>
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void (*signal(int <var>sig</var>, void(*<var>func</var>)(int))) (int);
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void (*_signal_r(void *<var>reent</var>, int <var>sig</var>, void(*<var>func</var>)(int))) (int);
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</pre></div>
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<p><strong>Description</strong><br>
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<code>signal</code> provides a simple signal-handling implementation for embedded
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targets.
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</p>
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<p><code>signal</code> allows you to request changed treatment for a particular
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signal <var>sig</var>. You can use one of the predefined macros <code>SIG_DFL</code>
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(select system default handling) or <code>SIG_IGN</code> (ignore this signal)
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as the value of <var>func</var>; otherwise, <var>func</var> is a function pointer
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that identifies a subroutine in your program as the handler for this signal.
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</p>
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<p>Some of the execution environment for signal handlers is
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unpredictable; notably, the only library function required to work
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correctly from within a signal handler is <code>signal</code> itself, and
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only when used to redefine the handler for the current signal value.
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</p>
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<p>Static storage is likewise unreliable for signal handlers, with one
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exception: if you declare a static storage location as ‘<code>volatile
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sig_atomic_t</code>’, then you may use that location in a signal handler to
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store signal values.
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</p>
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<p>If your signal handler terminates using <code>return</code> (or implicit
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return), your program’s execution continues at the point
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where it was when the signal was raised (whether by your program
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itself, or by an external event). Signal handlers can also
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use functions such as <code>exit</code> and <code>abort</code> to avoid returning.
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</p>
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<p>The alternate function <code>_signal_r</code> is the reentrant version.
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The extra argument <var>reent</var> is a pointer to a reentrancy structure.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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If your request for a signal handler cannot be honored, the result is
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<code>SIG_ERR</code>; a specific error number is also recorded in <code>errno</code>.
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</p>
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<p>Otherwise, the result is the previous handler (a function pointer or
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one of the predefined macros).
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</p>
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<br>
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<p><strong>Portability</strong><br>
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ANSI C requires <code>signal</code>.
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</p>
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<p>No supporting OS subroutines are required to link with <code>signal</code>, but
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it will not have any useful effects, except for software generated signals,
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without an operating system that can actually raise exceptions.
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</p>
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<br>
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<hr>
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<div class="header">
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<p>
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Previous: <a href="raise.html#raise" accesskey="p" rel="prev">raise</a>, Up: <a href="Signals.html#Signals" accesskey="u" rel="up">Signals</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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