std::numeric_limits::round_style

From cppreference.com


static const std::float_round_style round_style		(until C++11)

static constexpr std::float_round_style round_style		(since C++11)

The value of std::numeric_limits<T>::round_stylem identifies the rounding style used by the floating-point type T whenever a value that is not one of the exactly repesentable values of T is stored in an object of that type.

[edit] Standard specializations


`T`	value of std::numeric_limits<T>::round_style

/* non-specialized */	std::round_toward_zero

bool	std::round_toward_zero

char	std::round_toward_zero

signed char	std::round_toward_zero

unsigned char	std::round_toward_zero

wchar_t	std::round_toward_zero

char16_t	std::round_toward_zero

char32_t	std::round_toward_zero

short	std::round_toward_zero

unsigned short	std::round_toward_zero

int	std::round_toward_zero

unsigned int	std::round_toward_zero

long	std::round_toward_zero

unsigned long	std::round_toward_zero

long long	std::round_toward_zero

unsigned long long	std::round_toward_zero

float	usually std::round_to_nearest

double	usually std::round_to_nearest

long double	usually std::round_to_nearest

[edit] Example

The decimal value 0.1 cannot be represented by a binary floating-point type. When stored in an IEEE-745 double, it falls between $0x1.9999999999999*2 -4$ and $0x1.999999999999a*2 -4$ . Rounding to nearest representable value results in $0x1.999999999999a*2 -4$ .

Similarly, the decimal value 0.3, which is between $0x1.3333333333333*2 -2$ and $0x1.3333333333334*2 -2$ is rounded to nearest and is stored as $0x1.3333333333333*2 -2$ .

#include <iostream>
#include <limits>
int main()
{
    std::cout << std::hexfloat << "The decimal 0.1 is stored in a double as "
              << 0.1 << '\n'
              << "The decimal 0.3 is stored in a double as "
              << 0.3 << '\n'
              << "The rounding style is " << std::numeric_limits<double>::round_style << '\n';
}

Output:

The decimal 0.1 is stored in a double as 0x1.999999999999ap-4
The decimal 0.3 is stored in a double as 0x1.3333333333333p-2
The rounding style is 1

[edit] See also


float_round_style	indicates floating-point rounding modes (enum)

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