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, 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.


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


clears the specified floating-point status flags
determines which of the specified floating-point status flags are set
raises the specified floating-point exceptions
copies the state of the specified floating-point status flags from or to the floating-point environment
gets or sets rounding direction
saves or restores the current floating point environment
saves the environment, clears all status flags and ignores all future errors
restores the floating-point environment and raises the previously raise exceptions


floating-point exceptions
(macro constant)
floating-point rounding direction
(macro constant)
default floating-point environment
(macro constant)


  • 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