The feclearexcept() routine clears the floating-point exception flags specified by excepts, whereas feraiseexcept() raises the specified exceptions. Raising an exception causes the corresponding flag to be set, and a SIGFPE is delivered to the process if the exception is unmasked.

The fetestexcept() function determines which flags are currently set, of those specified by excepts.

The fegetexceptflag() function stores the state of the exception flags specified in excepts in the opaque object pointed to by flagp. Similarly, fesetexceptflag() changes the specified exception flags to reflect the state stored in the object pointed to by flagp. Note that the flags restored with fesetexceptflag() must be a (not necessarily proper) subset of the flags recorded by a prior call to fegetexceptflag().

For all of these functions, the possible types of exceptions include those described in fenv(3). Some architectures may define other types of floating-point exceptions.

Implementation notes

On some architectures, raising an overflow or underflow exception also causes an inexact exception to be raised. In these cases, the overflow or underflow will be raised first.

The fegetexceptflag() and fesetexceptflag() routines are preferred to fetestexcept() and feraiseexcept(), respectively, for saving and restoring exception flags. The latter do not re-raise exceptions and may preserve architecture-specific information such as addresses where exceptions occurred.

Library

Math Library (libm, -lm)

#include <fenv.h>
#pragma STDC FENV_ACCESS ON

int
feclearexcept(int excepts);

int
fegetexceptflag(fexcept_t *flagp, int excepts);

int
feraiseexcept(int excepts);

int
fesetexceptflag(const fexcept_t *flagp, int excepts);

int
fetestexcept(int excepts);

Return Values

• For feclearexcept, fegetexceptflag, feraiseexcep), and fesetexceptflag:

  0 (zero)

  Success.

  Any other value

  Failure.

• For fetestexcept:
  Returns the bitwise OR of the values of the current exception flags that were requested.

Standards

The feclearexcept(), fegetexceptflag(), feraiseexcept(), fesetexceptflag(), and fetestexcept() routines conform to ISO/IEC 9899:1999 (``ISO C99'').

History

See Also

sigaction(2), feholdexcept(3), fenv(3), feupdateenv(3), fpgetsticky(3), fpresetsticky(3)