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MATH_ERRNO, MATH_ERREXCEPT, math_errhandling

Description

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:

Constant Explanation MATH_ERREXCEPT indicates that floating-point exceptions are used: at least FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW are defined in <cfenv>. MATH_ERRNO indicates that floating-point operations use the variable errno to report errors.

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:

ConditionExplanationerrnofloating-point exceptionExample
Domain errorthe argument is outside the range in which the operation is mathematically defined (the description of each function lists the required domain errors)EDOMFE_INVALIDstd::acos(2)
Pole errorthe mathematical result of the function is exactly infinite or undefinedERANGEFE_DIVBYZEROstd::log(0.0), 1.0/0.0
Range error due to overflowthe mathematical result is finite, but becomes infinite after rounding, or becomes the largest representable finite value after rounding downERANGEFE_OVERFLOWstd::pow(DBL_MAX,2)
Range error due to underflowthe result is non-zero, but becomes zero after rounding, or becomes subnormal with a loss of precisionERANGE or unchanged (implementation-defined)FE_UNDERFLOW or nothing (implementation-defined)DBL_TRUE_MIN/2
Inexact resultthe result has to be rounded to fit in the destination typeunchangedFE_INEXACT or nothing (unspecified)std::sqrt(2), 1.0/10.0

Declarations

Since C++11
#define MATH_ERRNO        

#define MATH_ERREXCEPT

#define math_errhandling /*implementation defined*/

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.

Examples

#include <iostream>
#include <cfenv>
#include <cmath>
#include <cerrno>
#include <cstring>
#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";
}

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

MATH_ERRNO, MATH_ERREXCEPT, math_errhandling

Description

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:

Constant Explanation MATH_ERREXCEPT indicates that floating-point exceptions are used: at least FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW are defined in <cfenv>. MATH_ERRNO indicates that floating-point operations use the variable errno to report errors.

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:

ConditionExplanationerrnofloating-point exceptionExample
Domain errorthe argument is outside the range in which the operation is mathematically defined (the description of each function lists the required domain errors)EDOMFE_INVALIDstd::acos(2)
Pole errorthe mathematical result of the function is exactly infinite or undefinedERANGEFE_DIVBYZEROstd::log(0.0), 1.0/0.0
Range error due to overflowthe mathematical result is finite, but becomes infinite after rounding, or becomes the largest representable finite value after rounding downERANGEFE_OVERFLOWstd::pow(DBL_MAX,2)
Range error due to underflowthe result is non-zero, but becomes zero after rounding, or becomes subnormal with a loss of precisionERANGE or unchanged (implementation-defined)FE_UNDERFLOW or nothing (implementation-defined)DBL_TRUE_MIN/2
Inexact resultthe result has to be rounded to fit in the destination typeunchangedFE_INEXACT or nothing (unspecified)std::sqrt(2), 1.0/10.0

Declarations

Since C++11
#define MATH_ERRNO        

#define MATH_ERREXCEPT

#define math_errhandling /*implementation defined*/

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.

Examples

#include <iostream>
#include <cfenv>
#include <cmath>
#include <cerrno>
#include <cstring>
#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";
}

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