#define MATH_ERRNO 1
(since C99)#define MATH_ERREXCEPT 2
(since C99)#define math_errhandling /*implementation defined*/
(since C99)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:
MATH_ERREXCEPT indicates that floating-point exceptions are used: at least FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW are defined in <fenv.h>. 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:
Condition Explanation errno floating-point exception Example Domain error the argument is outside the range in which the operation is mathematically defined (the description of each function lists the required domain errors) EDOM FE_INVALID acos(2) Pole error the mathematical result of the function is exactly infinite or undefined ERANGE FE_DIVBYZERO log(0.0), 1.0/0.0 Range error due to overflow the mathematical result is finite, but becomes infinite after rounding, or becomes the largest representable finite value after rounding down ERANGE FE_OVERFLOW pow(DBL_MAX,2) Range error due to underflow the result is non-zero, but becomes zero after rounding, or becomes subnormal with a loss of precision ERANGE or unchanged (implementation-defined) FE_UNDERFLOW or nothing (implementation-defined) DBL_TRUE_MIN/2 Inexact result the result has to be rounded to fit in the destination type unchanged FE_INEXACT or nothing (unspecified) sqrt(2), 1.0/10.0 [edit] NotesWhether 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. rint vs nearbyint).
Before C99, floating-point exceptions were not specified, EDOM was required for any domain error, ERANGE was required for overflows and implementation-defined for underflows.
[edit] Example#include <stdio.h>
#include <fenv.h>
#include <math.h>
#include <errno.h>
#pragma STDC FENV_ACCESS ON
int main(void)
{
printf("MATH_ERRNO is %s\n", math_errhandling & MATH_ERRNO ? "set" : "not set");
printf("MATH_ERREXCEPT is %s\n",
math_errhandling & MATH_ERREXCEPT ? "set" : "not set");
feclearexcept(FE_ALL_EXCEPT);
errno = 0;
printf("log(0) = %f\n", log(0));
if(errno == ERANGE)
perror("errno == ERANGE");
if(fetestexcept(FE_DIVBYZERO))
puts("FE_DIVBYZERO (pole error) reported");
}
Possible output:
MATH_ERRNO is set MATH_ERREXCEPT is set log(0) = -inf errno = ERANGE: Numerical result out of range FE_DIVBYZERO (pole error) reported[edit] References
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