feupdateenv

#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;
}

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