double nearbyint ( double num );
/*floating-point-type*/
nearbyint ( /*floating-point-type*/ num );
float nearbyintf( float num );
(2) (since C++11)long double nearbyintl( long double num );
(3) (since C++11) template< /*math-floating-point*/ V >constexpr /*deduced-simd-t*/<V>
template< class Integer >
double nearbyint ( Integer num );
Rounds the floating-point argument
numto an integer value in floating-point format, using the
current rounding mode.
The library provides overloads ofstd::nearbyint
for all cv-unqualified floating-point types as the type of the parameter.(since C++23)
A) Additional overloads are provided for all integer types, which are treated as double.
(since C++11) [edit] Parameters num - floating-point or integer value [edit] Return valueThe nearest integer value to num, according to the current rounding mode, is returned.
[edit] Error handlingThis function is not subject to any of the errors specified in math_errhandling.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
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)).
[edit] Example#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[edit] See also
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