C++ llrint()用法及代碼示例

C++ llrint() 函數

llrint() 函數是 cmath 頭文件的庫函數，用於對給定值進行四舍五入並將其轉換為 long long 整數。它接受一個值 (float，double， 或者long double) 並根據指定的舍入方向舍入後返回一個長整型值fegetround()函數。

llrint() 函數的語法：

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); 

參數：

• x– 表示要舍入的值。

返回值：

這個函數的返回類型是long long int，它返回一個長整數值，四舍五入到附近的整數。

例：

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

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

C++代碼演示llrint()函數的例子

// 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;
}

輸出

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

參考：C++ llrint() 函數