| 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.
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
#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
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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