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MATH_ERRNO, MATH_ERREXCEPT, math_errhandling

Defined in header <math.h> 
#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:

- - - -
Constant Explanation
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.

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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

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. 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.

-

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

References

See also

- - -
-
(C99)
 floating-point exceptions
(macro constant)
macro which expands to POSIX-compatible thread-local error number variable
(macro variable)
C++ documentation for math_errhandling
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- © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
- https://en.cppreference.com/w/c/numeric/math/math_errhandling -

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