fegetround, fesetround

#include <stdio.h>
#include <math.h>
#include <fenv.h>
 
#pragma STDC FENV_ACCESS ON
void show_fe_current_rounding_method(void)
{
    printf("current rounding method:  ");
    switch (fegetround()) {
           case FE_TONEAREST:  printf ("FE_TONEAREST");  break;
           case FE_DOWNWARD:   printf ("FE_DOWNWARD");   break;
           case FE_UPWARD:     printf ("FE_UPWARD");     break;
           case FE_TOWARDZERO: printf ("FE_TOWARDZERO"); break;
           default:            printf ("unknown");
    };
    printf("\n");
}
 
int main(void)
{
    /* 默认舍入方法 */
    show_fe_current_rounding_method();
    printf("+11.5 -> %+4.1f\n", rint(+11.5)); /* 两整数的中央值 */
    printf("+12.5 -> %+4.1f\n", rint(+12.5)); /* 两整数的中央值 */
 
    /* 保存舍入方法。 */
    int curr_method = fegetround();
 
    /* 临时更改当前舍入方法。 */
    fesetround(FE_DOWNWARD);
    show_fe_current_rounding_method();
    printf("+11.5 -> %+4.1f\n", rint(+11.5));
    printf("+12.5 -> %+4.1f\n", rint(+12.5));
 
    /* 恢复舍入方法。 */
    fesetround(curr_method);
    show_fe_current_rounding_method(); 
 
    return 0;
}