C ++中的lround()函数对最接近参数的整数值进行四舍五入，在中间的情况下舍入为零。返回的值是long int类型。它类似于round()函数，但返回一个long int，而round返回与输入相同的数据类型。
long int lround(double x); long int lround(float x); long int lround(long double x); long int lround(T x); // For integral type
lround()函数采用单个参数，并返回long int类型的值。此函数在<cmath>头文件中定义。
lround()函数将单个参数值取整。
lround()函数返回最接近x的整数值，中间情况从零舍入。返回的值是long int类型。
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
long int result;
double x = 11.16;
result = lround(x);
cout << "lround(" << x << ") = " << result << endl;
x = 13.87;
result = lround(x);
cout << "lround(" << x << ") = " << result << endl;
x = 50.5;
result = lround(x);
cout << "lround(" << x << ") = " << result << endl;
x = -11.16;
result = lround(x);
cout << "lround(" << x << ") = " << result << endl;
x = -13.87;
result = lround(x);
cout << "lround(" << x << ") = " << result << endl;
x = -50.5;
result = lround(x);
cout << "lround(" << x << ") = " << result << endl;
return 0;
}运行该程序时，输出为：
lround(11.16) = 11 lround(13.87) = 14 lround(50.5) = 51 lround(-11.16) = -11 lround(-13.87) = -14 lround(-50.5) = -51
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
int x = 15;
long int result;
result = lround(x);
cout << "lround(" << x << ") = " << result << endl;
return 0;
}运行该程序时，输出为：
lround(15) = 15
对于整数值，应用lround函数将返回与输入相同的值。所以它在实际中并不常用来表示整数值。