FE_DIVBYZERO, FE_INEXACT, FE_INVALID, FE_OVERFLOW, FE_UNDERFLOW, FE_ALL_EXCEPT

 

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fegetexceptflag fesetexceptflag (C++11) (C++11)

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FE_ALL_EXCEPT FE_DIVBYZERO FE_INEXACT FE_INVALID FE_OVERFLOW FE_UNDERFLOW (C++11)

FE_DOWNWARD FE_TONEAREST FE_TOWARDZERO FE_UPWARD (C++11)

FE_DFL_ENV (C++11)

 

Defined in header <cfenv>
#define FE_DIVBYZERO    /*implementation defined power of 2*/		(since C++11)
#define FE_INEXACT      /*implementation defined power of 2*/		(since C++11)
#define FE_INVALID      /*implementation defined power of 2*/		(since C++11)
#define FE_OVERFLOW     /*implementation defined power of 2*/		(since C++11)
#define FE_UNDERFLOW    /*implementation defined power of 2*/		(since C++11)
#define FE_ALL_EXCEPT  FE_DIVBYZERO | FE_INEXACT | \                        FE_INVALID | FE_OVERFLOW |  \                        FE_UNDERFLOW		(since C++11)

All these macro constants (except FE_ALL_EXCEPT) expand to integer constant expressions that are distinct powers of 2, which uniquely identify all supported floating-point exceptions. Each macro is only defined if it is supported.

The macro constant FE_ALL_EXCEPT, which expands to the bitwise OR of all other FE_*, is always defined and is zero if floating-point exceptions are not supported by the implementation.

Constant	Explanation
FE_DIVBYZERO	division by zero occurred during the earlier floating-point operation
FE_INEXACT	inexact result: rounding was necessary to store the result of the earlier floating-point operation
FE_INVALID	invalid operation: the earlier floating-point operation could not performed
FE_OVERFLOW	the result of the earlier floating-point operation was too large to be representable
FE_UNDERFLOW	the result of the earlier floating-point operation was subnormal
FE_ALL_EXCEPT	bitwise OR of all supported floating-point exceptions

The implementation may define additional macro constants in <cfenv> to identify additional floating-point exceptions. All such constants begin with FE_ followed by at least one uppercase letter.

Example

#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