This documentation is archived and is not being maintained.


Resets the floating-point package.

void _fpreset( void );

The _fpreset function reinitializes the floating-point math package. _fpreset is usually used with signal, system, or the _exec or _spawn functions. If a program traps floating-point error signals (SIGFPE) with signal, it can safely recover from floating-point errors by invoking _fpreset and using longjmp.

This function is deprecated when compiling with /clr (Common Language Runtime Compilation) or /clr:pure because the common language runtime only supports the default floating-point precision.

Function Required header Compatibility



Windows 95, Windows 98, Windows 98 Second Edition, Windows Millennium Edition, Windows NT 4.0, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003

For more compatibility information, see Compatibility in the Introduction.

// crt_fpreset.c
// This program uses signal to set up a
// routine for handling floating-point errors.

#include <stdio.h>
#include <signal.h>
#include <setjmp.h>
#include <stdlib.h>
#include <float.h>
#include <math.h>
#include <string.h>

jmp_buf mark;              // Address for long jump to jump to
int     fperr;             // Global error number

void __cdecl fphandler( int sig, int num );   // Prototypes
void fpcheck( void );

int main( void )
   double n1 = 5.0;
   double n2 = 0.0;
   double r;
   int jmpret;

   // Unmask all floating-point exceptions. 
    _control87( 0, _MCW_EM );
   // Set up floating-point error handler. The compiler
   // will generate a warning because it expects
   // signal-handling functions to take only one argument.
   if( signal( SIGFPE, (void (__cdecl *)(int)) fphandler ) == SIG_ERR )
       fprintf( stderr, "Couldn't set SIGFPE\n" );

   // Save stack environment for return in case of error. First 
   // time through, jmpret is 0, so true conditional is executed. 
   // If an error occurs, jmpret will be set to -1 and false 
   // conditional will be executed.
   jmpret = setjmp( mark );
   if( jmpret == 0 )
      printf( "Dividing %4.3g by %4.3g...\n", n1, n2 );
      r = n1 / n2;
      // This won't be reached if error occurs.
      printf( "\n\n%4.3g / %4.3g = %4.3g\n", n1, n2, r );

      r = n1 * n2;
      // This won't be reached if error occurs.
      printf( "\n\n%4.3g * %4.3g = %4.3g\n", n1, n2, r );
// fphandler handles SIGFPE (floating-point error) interrupt. Note
// that this prototype accepts two arguments and that the 
// prototype for signal in the run-time library expects a signal 
// handler to have only one argument.
// The second argument in this signal handler allows processing of
// _FPE_ZERODIVIDE, all of which are Microsoft-specific symbols 
// that augment the information provided by SIGFPE. The compiler 
// will generate a warning, which is harmless and expected.

void fphandler( int sig, int num )
   // Set global for outside check since we don't want
   // to do I/O in the handler.
   fperr = num;

   // Initialize floating-point package. */

   // Restore calling environment and jump back to setjmp. Return 
   // -1 so that setjmp will return false for conditional test.
   longjmp( mark, -1 );

void fpcheck( void )
   char fpstr[30];
   switch( fperr )
   case _FPE_INVALID:
       strcpy_s( fpstr, sizeof(fpstr), "Invalid number" );
   case _FPE_OVERFLOW:
       strcpy_s( fpstr, sizeof(fpstr), "Overflow" );

       strcpy_s( fpstr, sizeof(fpstr), "Underflow" );
       strcpy_s( fpstr, sizeof(fpstr), "Divide by zero" );
       strcpy_s( fpstr, sizeof(fpstr), "Other floating point error" );
   printf( "Error %d: %s\n", fperr, fpstr );


Dividing    5 by    0...
Error 131: Divide by zero