FE_DFL_ENV

Defined in header <<fenv.h>>

1	`#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)

fegetenvfesetenv (C99)	saves or restores the current floating point environment (function)
feupdateenv (C99)	restores the floating-point environment and raises the previously raise exceptions (function)
C++ documentation for `FE_DFL_ENV`

FE_DFL_ENV

Example

References

See also