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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

Run this code

    #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

### [edit] 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)

### [edit] See also

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

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