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.
Contents |
[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] 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.
[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
| indicates floating-point rounding modes (enum) |