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FE_DFL_ENV

From cppreference.com
< c‎ | numeric‎ | fenv
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.

[edit] 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()
{
    /* Show default f-p environment. */
    printf("On startup:\n");
    show_fe_environment();
 
    /* Change f-p environment. */
    fesetround(FE_DOWNWARD);     /* change rounding mode                   */
    feraiseexcept(FE_INVALID);   /* some computation with invalid argument */
    printf("\nBefore restoration:\n");
    show_fe_environment();
 
    /* Restore default f-p environment. */
    fesetenv(FE_DFL_ENV);
    printf("\nAfter restoring default environment:\n");
    show_fe_environment();
 
    return 0;
}

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:  FE_INVALID
current rounding method:    FE_TONEAREST

[edit] See also

saves or restores the current floating point environment
(function) [edit]
restores the floating-point environment and raises the previously raise exceptions
(function) [edit]
C++ documentation for FE_DFL_ENV