Floating point environment

 

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Floating point environment

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The floating-point environment is the set of floating-point status flags and control modes supported by the implementation. It is thread-local, each thread inherits the initial state of its floating-point environment from the parent thread. Floating-point operations modify the floating-point status flags to indicate abnormal results or auxiliary information. The state of floating-point control modes affects the outcomes of some floating-point operations.

The floating-point environment access and modification is only meaningful when #pragma STDC FENV_ACCESS is set to ON. Otherwise the implementation is free to assume that floating-point control modes are always the default ones and that floating-point status flags are never tested or modified. In practice, few current compilers support the #pragma explicitly, but most compilers allow meaningful access to the floating-point environment anyway.

Types

Defined in header <fenv.h>
fenv_t	The type representing the entire floating-point environment
fexcept_t	The type representing all floating-point status flags collectively

Functions

feclearexcept (C99)	clears the specified floating-point status flags (function)
fetestexcept (C99)	determines which of the specified floating-point status flags are set (function)
feraiseexcept (C99)	raises the specified floating-point exceptions (function)
fegetexceptflag fesetexceptflag (C99) (C99)	copies the state of the specified floating-point status flags from or to the floating-point environment (function)
fegetround fesetround (C99) (C99)	gets or sets rounding direction (function)
fegetenv fesetenv (C99)	saves or restores the current floating point environment (function)
feholdexcept (C99)	saves the environment, clears all status flags and ignores all future errors (function)
feupdateenv (C99)	restores the floating-point environment and raises the previously raise exceptions (function)

Macros

FE_ALL_EXCEPT FE_DIVBYZERO FE_INEXACT FE_INVALID FE_OVERFLOW FE_UNDERFLOW (C99)	floating-point exceptions (macro constant)
FE_DOWNWARD FE_TONEAREST FE_TOWARDZERO FE_UPWARD (C99)	floating-point rounding direction (macro constant)
FE_DFL_ENV (C99)	default floating-point environment (macro constant)