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<title>GNU Scientific Library – Reference Manual: Handling floating point exceptions</title>
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<a name="Handling-floating-point-exceptions"></a>
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<p>
Next: <a href="GCC-warning-options-for-numerical-programs.html#GCC-warning-options-for-numerical-programs" accesskey="n" rel="next">GCC warning options for numerical programs</a>, Previous: <a href="Examining-floating-point-registers.html#Examining-floating-point-registers" accesskey="p" rel="previous">Examining floating point registers</a>, Up: <a href="Debugging-Numerical-Programs.html#Debugging-Numerical-Programs" accesskey="u" rel="up">Debugging Numerical Programs</a> [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Handling-floating-point-exceptions-1"></a>
<h3 class="section">A.3 Handling floating point exceptions</h3>
<a name="index-exceptions_002c-floating-point"></a>
<a name="index-floating-point-exceptions"></a>
<p>It is possible to stop the program whenever a <code>SIGFPE</code> floating
point exception occurs. This can be useful for finding the cause of an
unexpected infinity or <code>NaN</code>. The current handler settings can be
shown with the command <code>info signal SIGFPE</code>.
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) info signal SIGFPE
Signal Stop Print Pass to program Description
SIGFPE Yes Yes Yes Arithmetic exception
</pre></div>
<p>Unless the program uses a signal handler the default setting should be
changed so that SIGFPE is not passed to the program, as this would cause
it to exit. The command <code>handle SIGFPE stop nopass</code> prevents this.
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) handle SIGFPE stop nopass
Signal Stop Print Pass to program Description
SIGFPE Yes Yes No Arithmetic exception
</pre></div>
<p>Depending on the platform it may be necessary to instruct the kernel to
generate signals for floating point exceptions. For programs using GSL
this can be achieved using the <code>GSL_IEEE_MODE</code> environment variable
in conjunction with the function <code>gsl_ieee_env_setup</code> as described
in see <a href="IEEE-floating_002dpoint-arithmetic.html#IEEE-floating_002dpoint-arithmetic">IEEE floating-point arithmetic</a>.
</p>
<div class="example">
<pre class="example">(gdb) set env GSL_IEEE_MODE=double-precision
</pre></div>
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