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Non-Compliant Coding Example (Error Checking)

The exact treatment of error conditions from math functions is quite complicated (see C99 Section 7.12.1, "Treatment of error conditions").

The {{pow()}} function returns a very large number (appropriately positive or negative) on an overflow _range error_.   This very large number is defined in {{<math.h>}} as described by C99exact treatment of error conditions from math functions is quite complicated.  C99 Section 7.12.1 defines the following behavior for floating point overflow \[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\]:

A floating result overflows if the magnitude of the mathematical result is finite but so large that the mathematical result cannot be represented without extraordinary roundoff error in an object of the specified type. If a floating result overflows and default rounding is in effect, or if the mathematical result is an exact infinity from finite arguments (for example log(0.0)), then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or HUGE_VALL according to the return type, with the same sign as the correct value of the function; if the integer expression math_errhandling & MATH_ERRNO is nonzero, the integer expression errno acquires the value ERANGE; if the integer expression math_errhandling & MATH_ERREXCEPT is nonzero, the ''divide-by-zero'' floating-point exception is raised if the mathematical result is an exact infinity and the ''overflow'' floating-point exception is raised otherwise

The macro

Code Block
HUGE_VAL

expands to a positive double constant expression, not necessarily representable as a float. The macros

Code Block
HUGE_VALF HUGE_VALL

are respectively float and long double analogs of HUGE_VAL.

It is best not to check for errors by comparing the returned value against HUGE_VAL or zero 0 for several reasons. First of all, :

• these are in general valid (albeit unlikely) data values.

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• making such tests requires detailed knowledge of the various error returns for each math function.

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• there are three different possibilities, -HUGE_VAL, 0, and HUGE_VAL, and you must know which are possible in each case.

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• different versions of the library have differed in their error-return behavior.

It is also difficult to check for math errors using {{errno}} because an implementation might not set it.

 For real functions, the programmer can test whether the implementation sets

 {{errno}} when {{math_errhandling & MATH_ERRNO}} is nonzero.

 For complex functions, the C99 Section 7.3.2 simply

 states "an implementation may set {{errno}} but is not required to" \[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\].

Compliant Solution (Error Checking)

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