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<head>
<title>
C Guide--2.9 signal.h
</title>
<!-- Changed by: eric huss, 12-Mar-1997 -->
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<body text="#000000" bgcolor="#FFFFFF">
<center>
<table border=0 width=100%>
<tr>
<td align=left width=20% valign=top>
<a href="2.8.html">
<img src="left.gif" border=0>
Previous Section<br>
2.8 setjmp.h</a></td>
<td align=center width=60% valign=top>
| <a href="index.html">Table of Contents</a> |
<a href="index2.html">Index</a> |</td>
<td align=right width=20% valign=top>
<a href="2.10.html">
Next Section
<img src="right.gif" border=0><br>
2.10 stdarg.h</a></td>
</tr>
</table>
</center>
<hr>
<h1> 2.9 signal.h</h1>
<p>
The signal header provides a means to handle signals reported during a program's
execution.
<p>
Macros:
<blockquote><code><b>
SIG_DFL<br>
SIG_ERR<br>
SIG_IGN<br>
SIGABRT<br>
SIGFPE<br>
SIGILL<br>
SIGINT<br>
SIGSEGV<br>
SIGTERM<br>
</b></code></blockquote>
Functions:
<blockquote><code><b>
signal();<br>
raise();<br>
</b></code></blockquote>
Variables:
<blockquote><code><b>
typedef sig_atomic_t
</b></code></blockquote>
<a name="variables"></a>
<h2>2.9.1 Variables and Definitions</h2>
<p>
The <code><b>sig_atomic_t</b></code> type is of type <code><b>int</b></code> and is used as a variable in a signal handler.
The <code><b>SIG_</b></code> macros are used with the signal function to define signal functions.
<table border=0>
<tr><td><code><b> SIG_DFL</b></code></td><td> Default handler.</td></tr>
<tr><td><code><b> SIG_ERR</b></code></td><td> Represents a signal error.</td></tr>
<tr><td><code><b> SIG_IGN</b></code></td><td> Signal ignore.</td></tr>
</table>
<p>
The <code><b>SIG</b></code> macros are used to represent a signal number in the following conditions:
<table border=0>
<tr><td><code><b> SIGABRT</b></code></td><td> Abnormal termination (generated by the abort function).</td></tr>
<tr><td><code><b> SIGFPE</b></code></td><td> Floating-point error (error caused by division by zero, invalid operation, etc.). </td></tr>
<tr><td><code><b> SIGILL</b></code></td><td> Illegal operation (instruction).</td></tr>
<tr><td><code><b> SIGINT </b></code></td><td> Interactive attention signal (such as ctrl-C).</td></tr>
<tr><td><code><b> SIGSEGV</b></code></td><td> Invalid access to storage (segment violation, memory violation).</td></tr>
<tr><td><code><b> SIGTERM </b></code></td><td> Termination request.</td></tr>
</table>
<a name="signal"></a>
<h2>2.9.2 signal</h2>
<p>
Declaration:
<blockquote>
<code><b>void (*signal(int</b></code><i> sig</i><code><b>, void (*</b></code><i>func</i><b><code>)(int)))(int);</b></code>
</blockquote
<p>
Controls how a signal is handled. <i>sig</i> represents the signal number compatible with the
<code><b>SIG</b></code> macros. <i>func</i> is the function to be called when the signal occurs. If func is <code><b>SIG_DFL</b></code>, then
the default handler is called. If <i>func</i> is <code><b>SIG_IGN</b></code>, then the signal is ignored. If <i>func</i> points to a
function, then when a signal is detected the default function is called (<code><b>SIG_DFL</b></code>), then the
function is called. The function must take one argument of type <code><b>int</b></code> which represents the signal
number. The function may terminate with <code><b>return</b></code>, <code><b>abort</b></code>, <code><b>exit</b></code>, or <code><b>longjmp</b></code>. When the function
terminates execution resumes where it was interrupted (unless it was a <code><b>SIGFPE</b></code> signal in which
case the result is undefined).
<p>
If the call to signal is successful, then it returns a pointer to the previous signal handler
for the specified signal type. If the call fails, then <code><b>SIG_ERR</b></code> is returned and <code><b>errno</b></code> is set
appropriately.
<p>
<a name="raise"></a>
<h2>2.9.3 raise</h2>
<p>
Declaration
<blockquote>
<code><b>int raise(int </b></code><i>sig</i><code><b>);</b></code>
</blockquote>
Causes signal <i>sig</i> to be generated. The <i>sig</i> argument is compatible with the <code><b>SIG</b></code> macros.
<p>
If the call is successful, zero is returned. Otherwise a nonzero value is returned.
<p>
Example:
<blockquote><code><b><pre>
#include&lt;signal.h&gt;
#include&lt;stdio.h&gt;
void catch_function(int);
int main(void)
{
if(signal(SIGINT, catch_function)==SIG_ERR)
{
printf("An error occured while setting a signal handler.\n");
exit(0);
}
printf("Raising the interactive attention signal.\n");
if(raise(SIGINT)!=0)
{
printf("Error raising the signal.\n");
exit(0);
}
printf("Exiting.\n");
return 0;
}
void catch_function(int signal)
{
printf("Interactive attention signal caught.\n");
}
</pre></b></code></blockquote>
The output from the program should be (assuming no errors):<br>
<pre>
Raising the interactive attention signal.
Interactive attention signal caught.
Exiting.
</pre>
<hr>
<center>
<table border=0 width=100%>
<tr>
<td align=left width=20% valign=top>
<a href="2.8.html">
<img src="left.gif" border=0>
Previous Section<br>
2.8 setjmp.h</a></td>
<td align=center width=60% valign=top>
| <a href="index.html">Table of Contents</a> |
<a href="index2.html">Index</a> |</td>
<td align=right width=20% valign=top>
<a href="2.10.html">
Next Section
<img src="right.gif" border=0><br>
2.10 stdarg.h</a></td>
</tr>
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</center>
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