1、圆整方向模式：
| 宏 | 描述 |
|---|---|
| FE_DOWNWARD | Round downward.（向下取整） |
| FE_TONEAREST | Round to nearest.（向最近取整） |
| FE_TOWARDZERO | Round toward zero.（向0取整） |
| FE_UPWARD | Round upward.（向上取整） |
2、int fesetround (int rdir);（#include ）
将当前浮点数的圆整方向模式设置为rdir
3、int fegetround (void); （#include ）
获得当前取整方向。
4、rint：使用fegetround 得到的取整方向将x取整为整数（注意返回类型并不是整型）
函数声明：
double rint (double x);
float rint (float x);
long double rint (long double x);
double rint (T x);
代码示例：
/* rint example */
#include <stdio.h> /* printf */
#include <fenv.h> /* fegetround, FE_* */
#include <math.h> /* rint */
int main ()
{
printf ("rounding using ");
switch (fegetround()) {
case FE_DOWNWARD: printf ("downward"); break;
case FE_TONEAREST: printf ("to-nearest"); break;
case FE_TOWARDZERO: printf ("toward-zero"); break;
case FE_UPWARD: printf ("upward"); break;
default: printf ("unknown");
}
printf (" rounding:\n");
printf ( "rint (2.3) = %.1f\n", rint(2.3) );
printf ( "rint (3.8) = %.1f\n", rint(3.8) );
printf ( "rint (-2.3) = %.1f\n", rint(-2.3) );
printf ( "rint (-3.8) = %.1f\n", rint(-3.8) );
return 0;
}
运行结果：
rounding using to-nearest rounding:
rint (2.3) = 2.0
rint (3.8) = 4.0
rint (-2.3) = -2.0
rint (-3.8) = -4.0
5、lrint：使用fegetround 得到的取整方向将x取整为整数
函数声明：
long int lrint (double x);
long int lrint (float x);
long int lrint (long double x);
long int lrint (T x);
6、llrint：使用fegetround 得到的取整方向将x取整为整数
函数声明：
long long int llrint (double x);
long long int llrint (float x);
long long int llrint (long double x);
long long int llrint (T x);
7、nearbyint ：使用fegetround 得到的取整方向将x取整为整数
函数声明：
double nearbyint (double x);
float nearbyint (float x);
long double nearbyint (long double x);
double nearbyint (T x);
8、trunc：向0取整
函数声明：
double trunc ( double x);
float trunc ( float x);
long double trunc (long double x);
double trunc (T x);
9、floor：向下取整
函数声明：
double floor (double x);
float floor (float x);
long double floor (long double x);
double floor (T x);
10、ceil：向上取整
函数声明：
double ceil (double x);
float ceil (float x);
long double ceil (long double x);
double ceil (T x);
/* round vs floor vs ceil vs trunc */
#include <stdio.h> /* printf */
#include <math.h> /* round, floor, ceil, trunc */
int main ()
{
const char * format = "%.1f \t%.1f \t%.1f \t%.1f \t%.1f\n";
printf ("value\tround\tfloor\tceil\ttrunc\n");
printf ("-----\t-----\t-----\t----\t-----\n");
printf (format, 2.3,round( 2.3),floor( 2.3),ceil( 2.3),trunc( 2.3));
printf (format, 3.8,round( 3.8),floor( 3.8),ceil( 3.8),trunc( 3.8));
printf (format, 5.5,round( 5.5),floor( 5.5),ceil( 5.5),trunc( 5.5));
printf (format,-2.3,round(-2.3),floor(-2.3),ceil(-2.3),trunc(-2.3));
printf (format,-3.8,round(-3.8),floor(-3.8),ceil(-3.8),trunc(-3.8));
printf (format,-5.5,round(-5.5),floor(-5.5),ceil(-5.5),trunc(-5.5));
return 0;
}
运行结果：
value round floor ceil trunc
----- ----- ----- ---- -----
2.3 2.0 2.0 3.0 2.0
3.8 4.0 3.0 4.0 3.0
5.5 6.0 5.0 6.0 5.0
-2.3 -2.0 -3.0 -2.0 -2.0
-3.8 -4.0 -4.0 -3.0 -3.0
-5.5 -6.0 -6.0 -5.0 -5.0
