Invokes a user-defined trap handler for IEEE floating-point exceptions.

int _fpieee_flt( 
   unsigned long excCode,
   struct _EXCEPTION_POINTERS *excInfo,
   int handler(_FPIEEE_RECORD *) 


  • excCode
    Exception code.

  • excInfo
    Pointer to the Windows NT exception information structure.

  • handler
    Pointer to the user's IEEE trap-handler routine.

Return Value

The return value of _fpieee_flt is the value returned by handler. As such, the IEEE filter routine might be used in the except clause of a structured exception-handling (SEH) mechanism.


The _fpieee_flt function invokes a user-defined trap handler for IEEE floating-point exceptions and provides it with all relevant information. This routine serves as an exception filter in the SEH mechanism, which invokes your own IEEE exception handler when necessary.

The _FPIEEE_RECORD structure, defined in Fpieee.h, contains information pertaining to an IEEE floating-point exception. This structure is passed to the user-defined trap handler by _fpieee_flt.



unsigned int RoundingMode, unsigned int Precision

These fields contain information about the floating-point environment at the time the exception occurred.

unsigned int Operation

Indicates the type of operation that caused the trap. If the type is a comparison (_FpCodeCompare), you can supply one of the special _FPIEEE_COMPARE_RESULT values (as defined in Fpieee.h) in the Result.Value field. The conversion type (_FpCodeConvert) indicates that the trap occurred during a floating-point conversion operation. You can look at the Operand1 and Result types to determine the type of conversion being attempted.


These structures indicate the types and values of the proposed result and operands:

OperandValid Flag indicating whether the responding value is valid.

Format Data type of the corresponding value. The format type might be returned even if the corresponding value is not valid.

Value Result or operand data value.


_FPIEEE_EXCEPTION_FLAGS contains one bit field per type of floating point exception.

There is a correspondence between these fields and the arguments used to mask the exceptions supplied to _controlfp.

The exact meaning of each bit depends on context:

Cause Each set bit indicates the particular exception that was raised.

Enable Each set bit indicates that the particular exception is currently unmasked.

Status Each set bit indicates that the particular exception is currently pending. This includes exceptions that have not been raised because they were masked by _controlfp.

Pending exceptions that are disabled are raised when you enable them. This can result in undefined behavior when using _fpieee_flt as an exception filter. Always call _clearfp before enabling floating point exceptions.



Required header



For more compatibility information, see Compatibility in the Introduction.


// crt_fpieee.c
// This program demonstrates the implementation of
// a user-defined floating-point exception handler using the
// _fpieee_flt function.

#include <fpieee.h>
#include <excpt.h>
#include <float.h>
#include <stddef.h>

int fpieee_handler( _FPIEEE_RECORD * );

int fpieee_handler( _FPIEEE_RECORD *pieee )
   // user-defined ieee trap handler routine:
   // there is one handler for all 
   // IEEE exceptions

   // Assume the user wants all invalid 
   // operations to return 0.

   if ((pieee->Cause.InvalidOperation) && 
       (pieee->Result.Format == _FpFormatFp32)) 
        pieee->Result.Value.Fp32Value = 0.0F;


#define _EXC_MASK    \
    _EM_UNDERFLOW  + \
    _EM_OVERFLOW   + \

int main( void )
   // ...

   __try {
      // unmask invalid operation exception
      _controlfp_s(NULL, _EXC_MASK, _MCW_EM); 

      // code that may generate 
      // fp exceptions goes here
   __except ( _fpieee_flt( GetExceptionCode(),
                fpieee_handler ) ){

      // code that gets control 

      // if fpieee_handler returns


   // ...

.NET Framework Equivalent

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.

See Also


Floating-Point Support

_control87, _controlfp, __control87_2