std::numeric_limits::round_style

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_style 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.

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`

Notes

These values are constants, and do not reflect the changes to the rounding made by std::fesetround. The changed values may be obtained from FLT_ROUNDS or std::fegetround.

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

std::numeric_limits::round_style

Standard specializations

Notes

Example

See also