C++ llrint() Function Usage and Example

C++ Library Function <cmath>

C ++The llrint() function uses the current rounding mode to round the parameter to an integer value.

The current rounding mode is determined by the fesetround() function. It is similar tolrint()But returns long long int instead of long int.

llrint() prototype[From C ++ 11Standard start]

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);　//For integer

The llrint() function takes a single parameter and returns a value of type long long int. This function is in<cmath>Defined in the header file.

llrint() parameters

The llrint() function truncates a single parameter value.

llrint() return value

The llrint() function rounds the parameter x to an integer value using the rounding direction specified by fegetround() and returns the value in the form of long long int.

By default, the rounding direction is set to 'to-nearest'.

You can use the fesetround() function to set the rounding direction to other values.

Example1：How llrint() works in C ++In what works?

#include <iostream>
#include <cmath>
#include <cfenv>
using namespace std;
int main()
{
　　　　//By default, the rounding direction is the nearest direction, i.e., fesetround(FE_TONEAREST)
　　　　double x =　11.87;
　　　　long long int result;
　　　　result　=　llrint(x);
　　　　cout << "Round to the nearest (" << x << ") = " << result << endl;
　　　　
　　　　//Midpoint rounded up to a higher integer
　　　　x =　11.5;
　　　　result　=　llrint(x);
　　　　cout << "Round to the nearest (" << x << ") = " << result << endl;
　　　　//　Set the rounding direction to DOWNWARD
　　　　fesetround(FE_DOWNWARD);
　　　　x =　11.87;
　　　　result　=　llrint(x);
　　　　cout　<<　"Round Down ("　<<　x　<<　") = "　<<　result　<<　endl;
　　　　
　　　　//　Set the rounding direction to UPWARD
　　　　fesetround(FE_UPWARD);
　　　　x =　33.32;
　　　　result　=　llrint(x);
　　　　cout << "Round up (" << x << ") = " << result << endl;
　　　　
　　　　return　0;
}

When running the program, the output is:

Round to the nearest (11.87)　=　12
Round to the nearest (11.5)　=　12
Round Down (11.8699)　=　11
Round up (33.3201)　=　34

Example2：The llrint() function of integer type

#include <iostream>
#include <cmath>
#include <cfenv>
using namespace std;
int main()
{
　　　　int x =　15;
　　　　long long int result;
　　　　
　　　　//Set the rounding direction to DOWNWARD
　　　　fesetround(FE_DOWNWARD);
　　　　result　=　llrint(x);
　　　　cout　<<　"Round Down ("　<<　x　<<　") = "　<<　result　<<　endl;
　　　　return　0;
}

When running the program, the output is:

Round Down (15)　=　15

For integer values, the llrint function will return the same value as the input. Therefore, it is not commonly used to represent integer values in practice.

C++ Library Function <cmath>