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<h1 id="firstHeading" class="firstHeading">feclearexcept</h1> <table class="t-dcl-begin"> <tr class="t-dsc-header"> <th> Defined in header <code><fenv.h></code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">int feclearexcept( int excepts );</pre>
</td> <td class="t-dcl-nopad"> </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> </table> <p>Attempts to clear the floating-point exceptions that are listed in the bitmask argument <code>excepts</code>, which is a bitwise OR of the <a href="fe_exceptions" title="c/numeric/fenv/FE exceptions">floating-point exception macros</a>.</p>
<h3 id="Parameters"> Parameters</h3> <table class="t-par-begin"> <tr class="t-par"> <td> excepts </td> <td> - </td> <td> bitmask listing the exception flags to clear </td>
</tr>
</table> <h3 id="Return_value"> Return value</h3> <p><code>0</code> if all indicated exceptions were successfully cleared or if <code>excepts</code> is zero. Returns a non-zero value on error.</p>
<h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include <fenv.h>
#include <stdio.h>
#include <math.h>
#include <float.h>
/*
* A possible implementation of hypot which makes use of many advanced
* floating-point features.
*/
double hypot_demo(double a, double b) {
const int range_problem = FE_OVERFLOW | FE_UNDERFLOW;
feclearexcept(range_problem);
// try a fast algorithm
double result = sqrt(a * a + b * b);
if (!fetestexcept(range_problem)) // no overflow or underflow
return result; // return the fast result
// do a more complicated calculation to avoid overflow or underflow
int a_exponent,b_exponent;
frexp(a, &a_exponent);
frexp(b, &b_exponent);
if (a_exponent - b_exponent > DBL_MAX_EXP)
return fabs(a) + fabs(b); // we can ignore the smaller value
// scale so that fabs(a) is near 1
double a_scaled = scalbn(a, -a_exponent);
double b_scaled = scalbn(b, -a_exponent);
// overflow and underflow is now impossible
result = sqrt(a_scaled * a_scaled + b_scaled * b_scaled);
// undo scaling
return scalbn(result, a_exponent);
}
int main(void)
{
// Normal case takes the fast route
printf("hypot(%f, %f) = %f\n", 3.0, 4.0, hypot_demo(3.0, 4.0));
// Extreme case takes the slow but more accurate route
printf("hypot(%e, %e) = %e\n", DBL_MAX / 2.0,
DBL_MAX / 2.0,
hypot_demo(DBL_MAX / 2.0, DBL_MAX / 2.0));
return 0;
}</pre></div> <p>Output:</p>
<div class="text source-text"><pre data-language="c">hypot(3.000000, 4.000000) = 5.000000
hypot(8.988466e+307, 8.988466e+307) = 1.271161e+308</pre></div> </div> <h3 id="References"> References</h3> <ul>
<li> C11 standard (ISO/IEC 9899:2011): </li>
<ul><li> 7.6.2.1 The feclearexcept function (p: 209) </li></ul>
<li> C99 standard (ISO/IEC 9899:1999): </li>
<ul><li> 7.6.2.1 The feclearexcept function (p: 190) </li></ul>
</ul> <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td> <div><a href="fetestexcept" title="c/numeric/fenv/fetestexcept"> <span class="t-lines"><span>fetestexcept</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> determines which of the specified floating-point status flags are set <br> <span class="t-mark">(function)</span> </td>
</tr> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/numeric/fenv/feclearexcept" title="cpp/numeric/fenv/feclearexcept">C++ documentation</a></span> for <code>feclearexcept</code> </td>
</tr> </table> <div class="_attribution">
<p class="_attribution-p">
© cppreference.com<br>Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.<br>
<a href="https://en.cppreference.com/w/c/numeric/fenv/feclearexcept" class="_attribution-link">https://en.cppreference.com/w/c/numeric/fenv/feclearexcept</a>
</p>
</div>
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