fetestexcept()

Updated: May 06, 2022

Determine which of the specified floating-point status flags are set

Synopsis:

#include <fenv.h>

int fetestexcept( const int excepts );

Arguments:

excepts
A bitwise OR of the flags that you want to check; zero or more of the following:
  • FE_ALL_EXCEPT — all the bits
  • FE_DENORMAL — the result of a floating-point expression is a denormalized number
  • FE_DIVBYZERO — pole error
  • FE_INEXACT — the result can't be exactly represented as a floating-point number
  • FE_INVALID — domain error
  • FE_OVERFLOW — result is too large to be representable
  • FE_UNDERFLOW — result is subnormal with a loss of precision

Library:

libm
The general-purpose math library.
libm-sve
(QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

Description:

The fetestexcept() function determines which of the specified floating-point exceptions are currently set.

Returns:

A bitwise OR of the flags that are in excepts and that correspond to floating-point exceptions that are currently set.

Examples:

#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <stdlib.h>

int main( void )
{
    int except_flags;

    /* acos(2) should raise a "domain error" exception. */

    feclearexcept(FE_ALL_EXCEPT);
    printf( "acos(2) is %f\n", acos(2) );
    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags & FE_INVALID)
        puts("FE_INVALID (domain error) reported");

    return EXIT_SUCCESS;
}

Classification:

C99, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes