FE_DFL_ENV

 

C

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Program utilities

Variadic function support

Error handling

Dynamic memory management

Strings library

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Numerics

Date and time utilities

Input/output support

Localization support

Concurrency support (C11)

Technical Specifications

Symbol index

 

Numerics

Common mathematical functions

Floating-point environment (C99)

Pseudo-random number generation

Complex number arithmetics (C99)

Type-generic math (C99)

 

Floating-point environment

Functions

feclearexcept (C99)

fetestexcept (C99)

feraiseexcept (C99)

fegetexceptflagfesetexceptflag (C99)(C99)

fegetroundfesetround (C99)(C99)

fegetenvfesetenv (C99)

feholdexcept (C99)

feupdateenv (C99)

Macro constants

FE_ALL_EXCEPTFE_DIVBYZEROFE_INEXACTFE_INVALIDFE_OVERFLOWFE_UNDERFLOW (C99)

FE_DOWNWARDFE_TONEARESTFE_TOWARDZEROFE_UPWARD (C99)

FE_DFL_ENV (C99)

 

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

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

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

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)