fegetexceptflag, fesetexceptflag

 

C

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Date and time utilities

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Technical Specifications

Symbol index

 

Numerics

Common mathematical functions

Floating-point environment (C99)

Pseudo-random number generation

Complex number arithmetics (C99)

Type-generic math (C99)

 

Floating-point environment

Functions

feclearexcept (C99)

fetestexcept (C99)

feraiseexcept (C99)

fegetexceptflagfesetexceptflag (C99)(C99)

fegetroundfesetround (C99)(C99)

fegetenvfesetenv (C99)

feholdexcept (C99)

feupdateenv (C99)

Macro constants

FE_ALL_EXCEPTFE_DIVBYZEROFE_INEXACTFE_INVALIDFE_OVERFLOWFE_UNDERFLOW (C99)

FE_DOWNWARDFE_TONEARESTFE_TOWARDZEROFE_UPWARD (C99)

FE_DFL_ENV (C99)

 

Defined in header <fenv.h>
int fegetexceptflag( fexcept_t* flagp, int excepts );	(1)	(since C99)
int fesetexceptflag( const fexcept_t* flagp, int excepts );	(2)	(since C99)

1) Attempts to obtain the full contents of the floating-point exception flags that are listed in the bitmask argument excepts, which is a bitwise OR of the floating-point exception macros.

2) Attempts to copy the full contents of the floating-point exception flags that are listed in excepts from flagp into the floating-point environment. Does not raise any exceptions, only modifies the flags.

The full contents of a floating-point exception flag is not necessarily a boolean value indicating whether the exception is raised or cleared. For example, it may be a struct which includes the boolean status and the address of the code that triggered the exception. These functions obtain all such content and obtain/store it in flagp in implementation-defined format.

Parameters

flagp	-	pointer to an fexcept_t object where the flags will be stored or read from
excepts	-	bitmask listing the exception flags to get/set

Return value

​0​ on success, non-zero otherwise.

Example

Run this code

#include <stdio.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");
}
 
int main(void)
{
    fexcept_t excepts;
 
    /* Setup a "current" set of exception flags. */
    feraiseexcept(FE_INVALID);
    show_fe_exceptions();
 
    /* Save current exception flags. */
    fegetexceptflag(&excepts,FE_ALL_EXCEPT);
 
    /* Temporarily raise two other exceptions. */
    feclearexcept(FE_ALL_EXCEPT);
    feraiseexcept(FE_OVERFLOW | FE_INEXACT);
    show_fe_exceptions();
 
    /* Restore previous exception flags. */
    fesetexceptflag(&excepts,FE_ALL_EXCEPT);
    show_fe_exceptions();
 
    return 0;
}

Output:

current exceptions raised: FE_INVALID
current exceptions raised: FE_INEXACT FE_OVERFLOW
current exceptions raised: FE_INVALID

References

• C11 standard (ISO/IEC 9899:2011):

• 7.6.2.2 The fegetexceptflag function (p: 210)

• 7.6.2.4 The fesetexceptflag function (p: 211)

• C99 standard (ISO/IEC 9899:1999):

• 7.6.2.2 The fegetexceptflag function (p: 191)

• 7.6.2.4 The fesetexceptflag function (p: 192)

See also