_fpreset
重設浮點套件。
void _fpreset( void );
備註
_fpreset 函式重新初始化浮點算術套件。 _fpreset 通常搭配 signal、 system、 _exec 或 _spawn 函式使用。 如果程式以 signal 攔截浮點錯誤信號 (SIGFPE)，它可以叫用 _fpreset 並使用 longjmp 從浮點錯誤安全地復原。
這個函式現在已不建議在 /clr (Common Language Runtime 編譯) 或 /clr:pure 下編譯時使用，因為 Common Language Runtime 只支援預設浮點精準度。
需求
功能 |
必要的標頭 |
|---|---|
_fpreset |
<float.h> |
如需更多關於相容性的資訊，請參閱入門介紹中的 相容性 (Compatibility) 。
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 );
}