_fpreset

重設浮點套件。

語法

void _fpreset( void );

備註

_fpreset 函式會重新初始化浮點數學套件。 _fpreset通常會與 、 system或 _spawn 函_exec式搭配signal使用。 如果程式使用 signal 來捕捉浮點錯誤信號 (SIGFPE)，則可以叫用 _fpreset 和使用 longjmp 來安全地復原浮點錯誤。

使用 /clr 編譯時 ，此函式已被取代，因為 Common Language Runtime 只支援預設浮點精確度。

需求

函式	必要的標頭
_fpreset	<float.h>

如需相容性詳細資訊，請參閱相容性。

範例

// 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

另請參閱

數學與浮點支援
_exec、_wexec 函式
signal
_spawn、_wspawn 函式
system, _wsystem