C++ llrint()用法及代码示例

C++ llrint() 函数

llrint() 函数是 cmath 头文件的库函数，用于对给定值进行四舍五入并将其转换为 long long 整数。它接受一个值 (float，double， 或者long double) 并根据指定的舍入方向舍入后返回一个长整型值fegetround()函数。

llrint() 函数的语法：

C++11：

    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); 

参数：

• x– 表示要舍入的值。

返回值：

这个函数的返回类型是long long int，它返回一个长整数值，四舍五入到附近的整数。

例：

    Input:
    float x = 123.4f;
    
    Function call:
    llrint(x);
    
    Output:
    123

    Input:
    float x = 123.5f;
    
    Function call:
    llrint(x);
    
    Output:
    124

C++代码演示llrint()函数的例子

// C++ code to demonstrate the example of
// llrint() function

#include <iostream>
#include <cmath>
#include <fenv.h> // for fegetround()
using namespace std;

int main()
{
    float x = 0.0f;

    cout << "Specified rounding is:";
    switch (fegetround()) {
    case FE_DOWNWARD:
        cout << "Downward" << endl;
        break;
    case FE_TONEAREST:
        cout << "To-nearest" << endl;
        break;
    case FE_TOWARDZERO:
        cout << "Toward-zero" << endl;
        break;
    case FE_UPWARD:
        cout << "Upward" << endl;
        break;
    default:
        cout << "Unknown" << endl;
    }

    x = 123.4f;
    cout << "llrint(" << x << "):" << llrint(x) << endl;

    x = 123.5f;
    cout << "llrint(" << x << "):" << llrint(x) << endl;

    x = 123.6f;
    cout << "llrint(" << x << "):" << llrint(x) << endl;

    x = -123.4f;
    cout << "llrint(" << x << "):" << llrint(x) << endl;

    x = -123.5f;
    cout << "llrint(" << x << "):" << llrint(x) << endl;

    x = -123.6f;
    cout << "llrint(" << x << "):" << llrint(x) << endl;

    return 0;
}

输出

Specified rounding is:To-nearest
llrint(123.4):123
llrint(123.5):124
llrint(123.6):124
llrint(-123.4):-123
llrint(-123.5):-124
llrint(-123.6):-124

参考：C++ llrint() 函数