_fpreset

 

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Resets the floating-point package.

Syntax

void _fpreset( void );  

Remarks

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.

Requirements

Function	Required header
_fpreset	<float.h>

For more compatibility information, see Compatibility in the Introduction.

Example

// 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" );  
       abort();  
    }  
  
   // 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 );  
   }  
   else  
      fpcheck();  
}  
// 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_INVALID, _FPE_OVERFLOW, _FPE_UNDERFLOW, and   
// _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. */  
   _fpreset();  
  
   // 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" );  
       break;  
   case _FPE_OVERFLOW:  
       strcpy_s( fpstr, sizeof(fpstr), "Overflow" );  
  
       break;  
   case _FPE_UNDERFLOW:  
       strcpy_s( fpstr, sizeof(fpstr), "Underflow" );  
       break;  
   case _FPE_ZERODIVIDE:  
       strcpy_s( fpstr, sizeof(fpstr), "Divide by zero" );  
       break;  
   default:  
       strcpy_s( fpstr, sizeof(fpstr), "Other floating point error" );  
       break;  
   }  
   printf( "Error %d: %s\n", fperr, fpstr );  
}  

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

See Also

Floating-Point Support
_exec, _wexec Functions
signal
_spawn, _wspawn Functions
system, _wsystem