# std::nearbyint, std::nearbyintf, std::nearbyintl

From cppreference.com
< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
| (1) |
float nearbyint ( float num ); double nearbyint ( double num ); long double nearbyint ( long double num ); |  | (until C++23)
/*floating-point-type*/ nearbyint ( /*floating-point-type*/ num ); |  | (since C++23)
float nearbyintf( float num ); | (2) | (since C++11)
long double nearbyintl( long double num ); | (3) | (since C++11)
SIMD overload (since C++26) |  |
Defined in header `<simd>` |  |
template< /*math-floating-point*/ V > constexpr /*deduced-simd-t*/<V> nearbyint ( const V& v_num ); | (S) | (since C++26)
Additional overloads (since C++11) |  |
Defined in header `<cmath>` |  |
template< class Integer > double nearbyint ( Integer num ); | (A) |

1-3) Rounds the floating-point argument num to an integer value in floating-point format, using the current rounding mode. The library provides overloads of `std::nearbyint` for all cv-unqualified floating-point types as the type of the parameter.(since C++23)

S) The SIMD overload performs an element-wise `std::nearbyint` on v_num.

    (See `math-floating-point` and `deduced-simd-t` for their definitions.)

(since C++26)

A) Additional overloads are provided for all integer types, which are treated as double. | (since C++11)

### Parameters

num | - | floating-point or integer value

### Return value

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

### 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 num is ±∞, it is returned, unmodified.
- If num is ±0, it is returned, unmodified.
- If num is NaN, NaN is returned.

### 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 std::rint, but unlike std::round).

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::nearbyint(num) has the same effect as std::nearbyint(static_cast<double>(num)).

### Example

Run this code

    #include <cfenv>
    #include <cmath>
    #include <iostream>
    #pragma STDC FENV_ACCESS ON

    int main()
    {
        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

### See also

rintrintfrintllrintlrintflrintlllrintllrintfllrintl (C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11) | nearest integer using current rounding mode with exception if the result differs (function)
roundroundfroundllroundlroundflroundlllroundllroundfllroundl (C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11) | nearest integer, rounding away from zero in halfway cases (function)
fegetroundfesetround (C++11)(C++11) | gets or sets rounding direction (function)
C documentation for nearbyint

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/numeric/math/nearbyint&oldid=160768"