std::fetestexcept

 

C++

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Technical Specifications

 

Numerics library

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gcd (C++17)

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accumulate

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Floating-point environment

Functions

feclearexcept (C++11)

fetestexcept (C++11)

feraiseexcept (C++11)

fegetexceptflagfesetexceptflag (C++11)(C++11)

fegetroundfesetround (C++11)(C++11)

fegetenvfesetenv (C++11)

feholdexcept (C++11)

feupdateenv (C++11)

Macro constants

FE_ALL_EXCEPTFE_DIVBYZEROFE_INEXACTFE_INVALIDFE_OVERFLOWFE_UNDERFLOW (C++11)

FE_DOWNWARDFE_TONEARESTFE_TOWARDZEROFE_UPWARD (C++11)

FE_DFL_ENV (C++11)

 

Defined in header <cfenv>
int fetestexcept( int excepts );		(since C++11)

Determines which of the specified subset of the floating point exceptions are currently set. The argument excepts is a bitwise OR of the floating point exception macros.

Parameters

excepts

-

bitmask listing the exception flags to test

Return value

Bitwise OR of the floating-point exception macros that are both included in excepts and correspond to floating-point exceptions currently set.

Example

Run this code

#include <iostream>
#include <cfenv>
#include <cmath>
 
#pragma STDC FENV_ACCESS ON
 
volatile double zero = 0.0; // volatile not needed where FENV_ACCESS is supported
volatile double one = 1.0;  // volatile not needed where FENV_ACCESS is supported
 
int main()
{
    std::feclearexcept(FE_ALL_EXCEPT);
    std::cout <<  "1.0/0.0 = " << 1.0 / zero << '\n';
    if(std::fetestexcept(FE_DIVBYZERO)) {
        std::cout << "division by zero reported\n";
    } else {
        std::cout << "divsion by zero not reported\n";
    }
 
    std::feclearexcept(FE_ALL_EXCEPT);
    std::cout << "1.0/10 = " << one/10 << '\n';
    if(std::fetestexcept(FE_INEXACT)) {
        std::cout << "inexact result reported\n";
    } else {
        std::cout << "inexact result not reported\n";
    }
 
    std::feclearexcept(FE_ALL_EXCEPT);
    std::cout << "sqrt(-1) = " << std::sqrt(-1) << '\n';
    if(std::fetestexcept(FE_INVALID)) {
        std::cout << "invalid result reported\n";
    } else {
        std::cout << "invalid result not reported\n";
    }
}

Output:

1.0/0.0 = inf
division by zero reported
1.0/10 = 0.1
inexact result reported
sqrt(-1) = -nan
invalid result reported

See also

feclearexcept (C++11)

clears the specified floating-point status flags (function)