feupdateenv

C

Language

Headers

Type support

Program utilities

Variadic function support

Error handling

Dynamic memory management

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Atomic operations (C11)

Thread support (C11)

Technical Specifications

Numerics

Common mathematical functions

Floating-point environment

Complex number arithmetics

Random number generation

Type-generic math

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>
int feupdateenv( const fenv_t* envp );		(since C99)

First, remembers the currently raised floating-point exceptions, then restores the floating-point environment from the object pointed to by envp (similar to fesetenv), then raises the floating-point exceptions that were saved.

This function may be used to end the non-stop mode established by an earlier call to feholdexcept.

Parameters

envp

-

pointer to the object of type fenv_t set by an earlier call to feholdexcept or fegetenv or equal to FE_DFL_ENV

Return value

0 on success, non-zero otherwise.

Example

Run this code

#include <stdio.h>
#include <fenv.h>
#include <float.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");
}

double x2 (double x)   /* times two */
{
    fenv_t curr_excepts;

    /* Save and clear current f-p environment. */
    feholdexcept(&curr_excepts);

    /* Raise inexact and overflow exceptions. */
    printf("In x2():  x =%f\n", x=x*2.0);
    show_fe_exceptions();
    feclearexcept(FE_INEXACT);   /* hide inexact exception from caller */

    /* Merge caller's exceptions (FE_INVALID)        */
    /* with remaining x2's exceptions (FE_OVERFLOW). */
    feupdateenv(&curr_excepts);
    return x;
}

int main(void)
{    
    feclearexcept(FE_ALL_EXCEPT);
    feraiseexcept(FE_INVALID);   /* some computation with invalid argument */
    show_fe_exceptions();
    printf("x2(DBL_MAX) =%f\n", x2(DBL_MAX));
    show_fe_exceptions();

    return 0;
}

Output:

current exceptions raised:  FE_INVALID
In x2():  x = inf
current exceptions raised:  FE_INEXACT FE_OVERFLOW
x2(DBL_MAX) = inf
current exceptions raised:  FE_INVALID FE_OVERFLOW

References

• C11 standard (ISO/IEC 9899:2011):

• 7.6.4.4 The feupdateenv function (p: 214-215)

• C99 standard (ISO/IEC 9899:1999):

• 7.6.4.4 The feupdateenv function (p: 195-196)

See also

feholdexcept (C99)	saves the environment, clears all status flags and ignores all future errors (function)
fegetenvfesetenv (C99)	saves or restores the current floating point environment (function)
FE_DFL_ENV (C99)	default floating-point environment (macro constant)