fegetenv, fesetenv
| 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)
Parameters
| envp | - | pointer to the object of type fenv_t which holds the status of the floating-point environment |
Return value
0 on success, non-zero otherwise.
Example
Run this code
#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
References
- C11 standard (ISO/IEC 9899:2011):
- 7.6.4.1 The fegetenv function (p: 213)
- 7.6.4.3 The fesetenv function (p: 214)
- C99 standard (ISO/IEC 9899:1999):
- 7.6.4.1 The fegetenv function (p: 194)
- 7.6.4.3 The fesetenv function (p: 195)
See also
| (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) |