程序代码：

#include <stdio.h>
#include <float.h>

int main( void )
{
   double a = 1e-40, b;
   float x, y;

   printf( "Status: %.4x - clear\n", _clear87()  );

   // Store into y is inexact and underflows:
   y = a;
   printf( "Status: %.4x - inexact, underflow\n", _clear87() );

   // y is denormal:

   b = y;
   printf( "Status: %.4x - denormal\n", _clear87() );
}

程序代码：

#include <stdio.h>
#include <fenv.h>

void fe_get_and_clear( void )
{
    int flag = fetestexcept(FE_ALL_EXCEPT);
    printf( "Status: %08X", flag );

    if( flag&FE_INVALID )
        printf( "%s", " invalid" );

    if( flag&FE_DENORMAL )
        printf( "%s", " denormal" );

    if( flag&FE_DIVBYZERO )
        printf( "%s", " divbyzero" );

    if( flag&FE_OVERFLOW )
        printf( "%s", " overflow" );

    if( flag&FE_UNDERFLOW )
        printf( "%s", " underflow" );

    if( flag&FE_INEXACT )
        printf( "%s", " inexact" );

    putchar( '\n' );
    feclearexcept(FE_ALL_EXCEPT);
}

int main( void )
{
    double a = 1e-40;
    fe_get_and_clear();

    float y = a;
    fe_get_and_clear();

    double b = y;
    fe_get_and_clear();

    printf( "%f %f %f\n", a, y, b );
}