MATH_ERRNO, MATH_ERREXCEPT, math_errhandling

Since C++11

Header: <cmath>

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).

# Declarations

#define MATH_ERRNO 1

(since C++11)

#define MATH_ERREXCEPT 2

(since C++11)

#define math_errhandling /*implementation defined*/

(since C++11)

# 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";
}

# See also