| Defined in header <<fenv.h>> | ||||
|---|---|---|---|---|
| (since C99) |
First, saves the current floating-point environment to the object pointed to by envp (similar to fegetenv), then clears all floating-point status flags, and then installs the non-stop mode: future floating-point exceptions will not interrupt execution (will not trap), until the floating-point environment is restored by feupdateenv or fesetenv.
This function may be used in the beginning of a subroutine that must hide the floating-point exceptions it may raise from the caller. If only some exceptions must be suppressed, while others must be reported, the non-stop mode is usually ended with a call to feupdateenv after clearing the unwanted exceptions.
Parameters
| envp | - | pointer to the object of type fenv_t where the floating-point environment will be stored |
Return value
0 on success, non-zero otherwise.
Example
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 | #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:
1 2 3 4 5 | current exceptions raised: FE_INVALIDIn x2(): x = infcurrent exceptions raised: FE_INEXACT FE_OVERFLOWx2(DBL_MAX) = infcurrent exceptions raised: FE_INVALID FE_OVERFLOW |
References
- C11 standard (ISO/IEC 9899:2011):
- 7.6.4.2 The feholdexcept function (p: 213-214)
- C99 standard (ISO/IEC 9899:1999):
- 7.6.4.2 The feholdexcept function (p: 194-195)
See also
| (C99) | restores the floating-point environment and raises the previously raise exceptions (function) |
| (C99) | saves or restores the current floating point environment (function) |
| (C99) | default floating-point environment (macro constant) |
C++ documentation for feholdexcept | |
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