C++ The usage and example of rint() function

C++ Library Function <cmath>

C ++The rint() function rounds the parameter to an integer value using the current rounding mode. The current rounding mode is determined by the function fesetround().

The rint() prototype [from C ++ 11Standard start]

double rint(double x);
float rint(float x);
long double rint(long double x);
double rint(T x);　//For integer

The rint() function takes a single parameter and returns a value of type double, float, or long double. This function is in<cmath>Defined in the header file.

The rint() parameter

The rint() function takes a single parameter and rounds it to an integer.

The rint() return value

The rint() function uses the rounding direction specified by fegetround() to round the parameter x to an integer value and returns this value. By default, the rounding direction is set to "nearest". You can use the fesetround() function to set the rounding direction to other values.

Example1：How does the rint() function work in C ++How does it work in C?

#include <iostream>
#include <cmath>
#include <cfenv>
using namespace std;
int main()
{
　　　　//By default, the rounding direction is the nearest direction, that is, fesetround(FE_TONEAREST)
　　　　double x =　11.87, result;
　　　　result　=　rint(x);
　　　　cout << "Round to the nearest (" << x << ") = " << result << endl;
　　　　
　　　　//Choose the higher value for the midpoint
　　　　x =　11.5;
　　　　result　=　rint(x);
　　　　cout << "Round to the nearest (" << x << ") = " << result << endl;
　　　　//　Set the rounding direction to DOWNWARD
　　　　fesetround(FE_DOWNWARD);
　　　　x =　11.87;
　　　　result　=　rint(x);
　　　　cout　<<　"Floor rounding ("　<<　x　<<　") = "　<<　result　<<　endl;
　　　　
　　　　//　Set the rounding direction to UPWARD
　　　　fesetround(FE_UPWARD);
　　　　x =　33.32;
　　　　result　=　rint(x);
　　　　cout << "Round up (" << x << ") = " << result << endl;
　　　　
　　　　return　0;
}

When the program is run, the output is:

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

Example2：The rint() function for integer type

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

When the program is run, the output is:

Floor rounding (15)　=　15

For integer values, the rint function will return the same value as the input. Therefore, it is usually not used for integral values in practice.

C++ Library Function <cmath>