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# std::nearbyint

From cppreference.com
< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
float nearbyint( float arg ); | (1) | (since C++11)
double nearbyint( double arg ); | (2) | (since C++11)
long double nearbyint( long double arg ); | (3) | (since C++11)
double nearbyint( Integral arg ); | (4) | (since C++11)

1-3) Rounds the floating-point argument `arg` to an integer value in floating-point format, using the current rounding mode.
4) A set of overloads or a function template accepting an argument of any integral type. Equivalent to (2) (the argument is cast to double).

### [edit] Parameters

arg | - | floating point value

### [edit] Return value

The nearest integer value to `arg`, according to the current rounding mode, is returned.

### [edit] Error handling

This function is not subject to any of the errors specified in math_errhandling

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

- FE_INEXACT is never raised
- If `arg` is ±∞, it is returned, unmodified
- If `arg` is ±0, it is returned, unmodified
- If `arg` is NaN, NaN is returned

### [edit] Notes

The only difference between `std::nearbyint` and std::rint is that `std::nearbyint` never raises FE_INEXACT.

The largest representable floating-point values are exact integers in all standard floating-point formats, so `std::nearbyint` never overflows on its own; however the result may overflow any integer type (including std::intmax_t), when stored in an integer variable.

If the current rounding mode is FE_TONEAREST, this function rounds to even in halfway cases (like rint, but unlike round).

### [edit] Example

Run this code

    #include <iostream>
    #include <cmath>
    #include <cfenv>

    int main()
    {
    #pragma STDC FENV_ACCESS ON
        std::fesetround(FE_TONEAREST);
        std::cout << "rounding to nearest: \n"
                  << "nearbyint(+2.3) = " << std::nearbyint(2.3)
                  << "  nearbyint(+2.5) = " << std::nearbyint(2.5)
                  << "  nearbyint(+3.5) = " << std::nearbyint(3.5) << '\n'
                  << "nearbyint(-2.3) = " << std::nearbyint(-2.3)
                  << "  nearbyint(-2.5) = " << std::nearbyint(-2.5)
                  << "  nearbyint(-3.5) = " << std::nearbyint(-3.5) << '\n';

        std::fesetround(FE_DOWNWARD);
        std::cout << "rounding down:\n"
                  << "nearbyint(+2.3) = " << std::nearbyint(2.3)
                  << "  nearbyint(+2.5) = " << std::nearbyint(2.5)
                  << "  nearbyint(+3.5) = " << std::nearbyint(3.5) << '\n'
                  << "nearbyint(-2.3) = " << std::nearbyint(-2.3)
                  << "  nearbyint(-2.5) = " << std::nearbyint(-2.5)
                  << "  nearbyint(-3.5) = " << std::nearbyint(-3.5) << '\n';

        std::cout << "nearbyint(-0.0) = " << std::nearbyint(-0.0)  << '\n'
                  << "nearbyint(-Inf) = " << std::nearbyint(-INFINITY) << '\n';
    }

Output:

    rounding to nearest:
    nearbyint(+2.3) = 2  nearbyint(+2.5) = 2  nearbyint(+3.5) = 4
    nearbyint(-2.3) = -2  nearbyint(-2.5) = -2  nearbyint(-3.5) = -4
    rounding down:
    nearbyint(+2.3) = 2  nearbyint(+2.5) = 2  nearbyint(+3.5) = 3
    nearbyint(-2.3) = -3  nearbyint(-2.5) = -3  nearbyint(-3.5) = -4
    nearbyint(-0.0) = -0
    nearbyint(-Inf) = -inf

### [edit] See also

rint lrint llrint (C++11)(C++11)(C++11) | nearest integer using current rounding mode with exception if the result differs (function) [edit]
round lround llround (C++11)(C++11)(C++11) | nearest integer, rounding away from zero in halfway cases (function) [edit]
fegetround fesetround (C++11)(C++11) | gets or sets rounding direction (function) [edit]
C documentation for nearbyint

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