Defined in header <fenv.h> | ||
|---|---|---|
int fegetenv( fenv_t* envp ); | (1) | (since C99) |
int fesetenv( const fenv_t* envp ); | (2) | (since C99) |
1) Attempts to store the status of the floating-point environment in the object pointed to by envp.
2) Attempts to establish the floating-point environment from the object pointed to by envp. The value of that object must be previously obtained by a call to feholdexcept or fegetenv or be a floating-point macro constant. If any of the floating-point status flags are set in envp, they become set in the environment (and are then testable with fetestexcept), but the corresponding floating-point exceptions are not raised (execution continues uninterrupted).
| envp | - | pointer to the object of type fenv_t which holds the status of the floating-point environment |
0 on success, non-zero otherwise.
#include <stdio.h>
#include <math.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(void)
{
fenv_t curr_env;
int rtn;
/* Show default environment. */
show_fe_environment();
printf("\n");
/* Perform some computation under default environment. */
printf("+11.5 -> %+4.1f\n", rint(+11.5)); /* midway between two integers */
printf("+12.5 -> %+4.1f\n", rint(+12.5)); /* midway between two integers */
show_fe_environment();
printf("\n");
/* Save current environment. */
rtn = fegetenv(&curr_env);
/* Perform some computation with new rounding method. */
feclearexcept(FE_ALL_EXCEPT);
fesetround(FE_DOWNWARD);
printf("1.0/0.0 = %f\n", 1.0/0.0);
printf("+11.5 -> %+4.1f\n", rint(+11.5));
printf("+12.5 -> %+4.1f\n", rint(+12.5));
show_fe_environment();
printf("\n");
/* Restore previous environment. */
rtn = fesetenv(&curr_env);
show_fe_environment();
return 0;
}Output:
current exceptions raised: none current rounding method: FE_TONEAREST +11.5 -> +12.0 +12.5 -> +12.0 current exceptions raised: FE_INEXACT current rounding method: FE_TONEAREST 1.0/0.0 = inf +11.5 -> +11.0 +12.5 -> +12.0 current exceptions raised: FE_DIVBYZERO FE_INEXACT current rounding method: FE_DOWNWARD current exceptions raised: FE_INEXACT current rounding method: FE_TONEAREST
|
(C99) | saves the environment, clears all status flags and ignores all future errors (function) |
|
(C99) | restores the floating-point environment and raises the previously raise exceptions (function) |
|
(C99) | default floating-point environment (macro constant) |
C++ documentation for fegetenv, fesetenv |
|
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