_fpreset
重置浮点包。
void _fpreset( void );
备注
_fpreset 函数初始化浮点运算包。 _fpreset 通常与 signal、system、_exec 或 _spawn 函数一起使用。 如果程序捕获signal浮点错误信号 (SIGFPE)，则可以通过调用 _fpreset 并使用 longjmp，从浮点错误安全恢复。
当使用 /clr（公共语言运行时编译） 或 /clr:pure 编译时，这些函数被丢弃，因为公共语言运行时 (CLR) 仅支持默认值浮点精度。
要求
功能 |
必需的标头 |
|---|---|
_fpreset |
<float.h> |
有关更多兼容性信息，请参见“简介”中的兼容性。
示例
// 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 );
}