Floating-point environment

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

• 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