MATH_ERRNO, MATH_ERREXCEPT, math_errhandling

The macro constant math_errhandling expands to an expression of type int that is either equal to MATH_ERRNO , or equal to MATH_ERREXCEPT , or equal to their bitwise OR ( MATH_ERRNO | MATH_ERREXCEPT ).

The value of math_errhandling indicates the type of error handling that is performed by the floating-point operators and functions :

If the implementation supports IEEE floating-point arithmetic (IEC 60559), math_errhandling & MATH_ERREXCEPT is required to be non-zero.

The following floating-point error conditions are recognized:

Notes

Whether FE_INEXACT is raised by the mathematical library functions is unspecified in general, but may be explicitly specified in the description of the function (e.g. std::rint vs std::nearbyint ).

Before C++11, floating-point exceptions were not specified, EDOM was required for any domain error, ERANGE was required for overflows and implementation-defined for underflows.

Example

#include <cerrno>
#include <cfenv>
#include <cmath>
#include <cstring>
#include <iostream>
// #pragma STDC FENV_ACCESS ON
 
int main()
{
    std::cout << "MATH_ERRNO is "
              << (math_errhandling & MATH_ERRNO ? "set" : "not set") << '\n'
              << "MATH_ERREXCEPT is "
              << (math_errhandling & MATH_ERREXCEPT ? "set" : "not set") << '\n';
    std::feclearexcept(FE_ALL_EXCEPT);
    errno = 0;
    std::cout <<  "log(0) = " << std::log(0) << '\n';
    if (errno == ERANGE)
        std::cout << "errno = ERANGE (" << std::strerror(errno) << ")\n";
    if (std::fetestexcept(FE_DIVBYZERO))
        std::cout << "FE_DIVBYZERO (pole error) reported\n";
}

MATH_ERRNO is set
MATH_ERREXCEPT is set
log(0) = -inf
errno = ERANGE (Numerical result out of range)
FE_DIVBYZERO (pole error) reported

See also