feholdexcept
From cppreference.com
C
Concurrency support (C11)
Floating-point environment
Functions
(C99)
(C99)
(C99)
(C99)(C99)
(C99)(C99)
(C99)
feholdexcept
(C99)
(C99)
Macro constants
(C99)
Defined in header
<fenv.h>
int feholdexcept( fenv_t* envp );
(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.
[edit] Parameters
envp
-
pointer to the object of type fenv_t where the floating-point environment will be stored
[edit] Return value
0 on success, non-zero otherwise.
[edit] 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
[edit] 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)
[edit] See also
(C99)
(function) [edit]
C++ documentation for feholdexcept