MATH_ERRNO, MATH_ERREXCEPT, math_errhandling
| Defined in header
<math.h>
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||
| #define MATH_ERRNO 1
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(since C99) | |
| #define MATH_ERREXCEPT 2
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(since C99) | |
| #define math_errhandling /*implementation defined*/
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(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
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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_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] 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.
[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] See also
| floating-point exceptions (macro constant) |
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| macro which expands to POSIX-compatible thread-local error number variable (macro variable) |
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C++ documentation for math_errhandling
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