Floating-point environment

 

C

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Technical Specifications

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Numerics

Common mathematical functions

Floating-point environment (C99)

Pseudo-random number generation

Complex number arithmetic (C99)

Type-generic math (C99)

 

Floating-point environment

Functions

feclearexcept (C99)

fetestexcept (C99)

feraiseexcept (C99)

fegetexceptflagfesetexceptflag (C99)(C99)

fegetroundfesetround (C99)(C99)

fegetenvfesetenv (C99)

feholdexcept (C99)

feupdateenv (C99)

Macro constants

FE_ALL_EXCEPTFE_DIVBYZEROFE_INEXACTFE_INVALIDFE_OVERFLOWFE_UNDERFLOW (C99)

FE_DOWNWARDFE_TONEARESTFE_TOWARDZEROFE_UPWARD (C99)

FE_DFL_ENV (C99)

 

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, such as HP aCC, Oracle Studio, and IBM XL, 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)
fegetexceptflagfesetexceptflag (C99)(C99)	copies the state of the specified floating-point status flags from or to the floating-point environment (function)
fegetroundfesetround (C99)(C99)	gets or sets rounding direction (function)
fegetenvfesetenv (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_EXCEPTFE_DIVBYZEROFE_INEXACTFE_INVALIDFE_OVERFLOWFE_UNDERFLOW (C99)	floating-point exceptions (macro constant)
FE_DOWNWARDFE_TONEARESTFE_TOWARDZEROFE_UPWARD (C99)	floating-point rounding direction (macro constant)
FE_DFL_ENV (C99)	default floating-point environment (macro constant)

References

• C23 standard (ISO/IEC 9899:2024):

• 7.6 Floating-point environment <fenv.h> (p: TBD)

• 7.31.4 Floating-point environment <fenv.h> (p: TBD)

• C17 standard (ISO/IEC 9899:2018):

• 7.6 Floating-point environment <fenv.h> (p: 150-156)

• 7.31.4 Floating-point environment <fenv.h> (p: 332)

• C11 standard (ISO/IEC 9899:2011):

• 7.6 Floating-point environment <fenv.h> (p: 206-215)

• 7.31.4 Floating-point environment <fenv.h> (p: 455)

• C99 standard (ISO/IEC 9899:1999):

• 7.6 Floating-point environment <fenv.h> (p: 187-196)

See also

C++ documentation for Floating-point environment