Defined in header <<fenv.h>> | ||
---|---|---|
#define FE_DFL_ENV /*implementation defined*/ | (since C99) |
The macro constant FE_DFL_ENV
expands to an expression of type const fenv_t*
, which points to a full copy of the default floating-point environment, that is, the environment as loaded at program startup.
Additional macros that begin with FE_
followed by uppercase letters, and have the type const fenv_t*
, may be supported by an implementation.
Example
#include <stdio.h> #include <fenv.h> #pragma STDC FENV_ACCESS ON void show_fe_exceptions(void) { printf("current exceptions raised: "); if(fetestexcept(FE_DIVBYZERO)) printf(" FE_DIVBYZERO"); if(fetestexcept(FE_INEXACT)) printf(" FE_INEXACT"); if(fetestexcept(FE_INVALID)) printf(" FE_INVALID"); if(fetestexcept(FE_OVERFLOW)) printf(" FE_OVERFLOW"); if(fetestexcept(FE_UNDERFLOW)) printf(" FE_UNDERFLOW"); if(fetestexcept(FE_ALL_EXCEPT)==0) printf(" none"); printf("\n"); } void show_fe_rounding_method(void) { printf("current rounding method: "); switch (fegetround()) { case FE_TONEAREST: printf ("FE_TONEAREST"); break; case FE_DOWNWARD: printf ("FE_DOWNWARD"); break; case FE_UPWARD: printf ("FE_UPWARD"); break; case FE_TOWARDZERO: printf ("FE_TOWARDZERO"); break; default: printf ("unknown"); }; printf("\n"); } void show_fe_environment(void) { show_fe_exceptions(); show_fe_rounding_method(); } int main() { printf("On startup:\n"); show_fe_environment(); // Change environment fesetround(FE_DOWNWARD); // change rounding mode feraiseexcept(FE_INVALID); // raise exception printf("\nBefore restoration:\n"); show_fe_environment(); fesetenv(FE_DFL_ENV); // restore printf("\nAfter restoring default environment:\n"); show_fe_environment(); }
Output:
On startup: current exceptions raised: none current rounding method: FE_TONEAREST Before restoration: current exceptions raised: FE_INVALID current rounding method: FE_DOWNWARD After restoring default environment: current exceptions raised: none current rounding method: FE_TONEAREST
References
- C11 standard (ISO/IEC 9899:2011):
- 7.6/9 Floating-point environment <fenv.h> (p: 208)
- C99 standard (ISO/IEC 9899:1999):
- 7.6/8 Floating-point environment <fenv.h> (p: 188-189)
See also
(C99) | saves or restores the current floating point environment (function) |
(C99) | restores the floating-point environment and raises the previously raise exceptions (function) |
C++ documentation for FE_DFL_ENV |
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