C++ rint()用法及代码示例

C++ 中的rint() 函数使用当前舍入模式将参数舍入为整数值。当前舍入模式由函数fesetround() 确定。

rint() 原型 [从 C++ 11 标准开始]

double rint(double x);
float rint(float x);
long double rint(long double x);
double rint(T x); // For integral type

rint() 函数采用单个参数并返回 double、float 或 long double 类型的值。该函数在<cmath> 头文件中定义。

参数：

rint() 函数采用单个参数值进行舍入。

返回：

rint() 函数使用 fegetround() 指定的舍入方向将参数 x 舍入为整数值并返回该值。默认情况下，舍入方向设置为'to-nearest'。可以使用fesetround() 函数将舍入方向设置为其他值。

示例 1：rint() 如何在 C++ 中工作？

#include <iostream>
#include <cmath>
#include <cfenv>
using namespace std;

int main()
{
    // by default, rounding direction is to-nearest i.e. fesetround(FE_TONEAREST)
    double x = 11.87, result;
    result = rint(x);
    cout << "Rounding to-nearest (" << x << ") = " << result << endl;
    
    // upper value is taken for mid-way values
    x = 11.5;
    result = rint(x);
    cout << "Rounding to-nearest (" << x << ") = " << result << endl;

    // setting rounding direction to DOWNWARD
    fesetround(FE_DOWNWARD);
    x = 11.87;
    result = rint(x);
    cout << "Rounding downward (" << x << ") = " << result << endl;
    
    // setting rounding direction to UPWARD
    fesetround(FE_UPWARD);
    x = 33.32;
    result = rint(x);
    cout << "Rounding upward (" << x << ") = " << result << endl;
    
    return 0;
}

运行程序时，输出将是：

Rounding to-nearest (11.87) = 12
Rounding to-nearest (11.5) = 12
Rounding downward (11.8699) = 11
Rounding upward (33.3201) = 34

示例 2：用于整数类型的 rint() 函数

#include <iostream>
#include <cmath>
#include <cfenv>
using namespace std;

int main()
{
    int x = 15;
    double result;
    
    // setting rounding direction to DOWNWARD
    fesetround(FE_DOWNWARD);
    result = rint(x);
    cout << "Rounding downward (" << x << ") = " << result << endl;

    return 0;
}

运行程序时，输出将是：

Rounding downward (15) = 15

对于整数值，应用 rint 函数返回与输入相同的值。所以在实践中它并不常用于整数值。