C++ rint()

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

rint() prototype [As of C++ 11 standard]

double rint(double x);
float rint(float x);
long double rint(long double x);
double rint(T x); // For integral type

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

rint() Parameters

The rint() function takes a single argument value to round.

rint() Return value

The rint() function rounds the argument x to an integral value, using the rounding direction specified by fegetround() and returns the value. By default, the rounding direction is set to 'to-nearest'. The rounding direction can be set to other values using fesetround() function.

Example 1: How rint() works in C++?

#include <iostream>
#include <cmath>
#include <cfenv>
using namespace std;

int main()
{
    // by default, rounding direction is to-nearest i.e. fesetround(FE_TONEAREST)
    double x = 11.87, result;
    result = rint(x);
    cout << "Rounding to-nearest (" << x << ") = " << result << endl;
    
    // upper value is taken for mid-way values
    x = 11.5;
    result = rint(x);
    cout << "Rounding to-nearest (" << x << ") = " << result << endl;

    // setting rounding direction to DOWNWARD
    fesetround(FE_DOWNWARD);
    x = 11.87;
    result = rint(x);
    cout << "Rounding downward (" << x << ") = " << result << endl;
    
    // setting rounding direction to UPWARD
    fesetround(FE_UPWARD);
    x = 33.32;
    result = rint(x);
    cout << "Rounding upward (" << x << ") = " << result << endl;
    
    return 0;
}

When you run the program, the output will be:

Rounding to-nearest (11.87) = 12
Rounding to-nearest (11.5) = 12
Rounding downward (11.8699) = 11
Rounding upward (33.3201) = 34

Example 2: rint() function for integral types

#include <iostream>
#include <cmath>
#include <cfenv>
using namespace std;

int main()
{
    int x = 15;
    double result;
    
    // setting rounding direction to DOWNWARD
    fesetround(FE_DOWNWARD);
    result = rint(x);
    cout << "Rounding downward (" << x << ") = " << result << endl;

    return 0;
}

When you run the program, the output will be:

Rounding downward (15) = 15

For integral values, applying the rint function returns the same value as the input. So it is not commonly used for integral values in practice.