# feclearexcept

< c‎ | numeric‎ | fenv

Floating-point environment
 Functions feclearexcept(C99) fetestexcept(C99) feraiseexcept(C99) fegetexceptflagfesetexceptflag(C99)(C99) fegetroundfesetround(C99)(C99) fegetenvfesetenv(C99) feholdexcept(C99) feupdateenv(C99) Macro constants FE_DFL_ENV(C99)

 Defined in header  int feclearexcept( int excepts ); (since C99)

Attempts to clear the floating-point exceptions that are listed in the bitmask argument excepts, which is a bitwise OR of the floating-point exception macros.

## Contents

### Parameters

 excepts - bitmask listing the exception flags to clear

### Return value

0 if all indicated exceptions were successfully cleared or if excepts is zero. Returns a non-zero value on error.

### Example

#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;
}

Output:

hypot(3.000000, 4.000000) = 5.000000
hypot(8.988466e+307, 8.988466e+307) = 1.271161e+308

### References

• C11 standard (ISO/IEC 9899:2011):
• 7.6.2.1 The feclearexcept function (p: 209)
• C99 standard (ISO/IEC 9899:1999):
• 7.6.2.1 The feclearexcept function (p: 190)

### See also

 fetestexcept(C99) determines which of the specified floating-point status flags are set (function)  C++ documentation for feclearexcept