# std::numeric_limits<T>::round_style

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< cpp‎ | types‎ | numeric limits

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
char8_t (since C++20) | std::round_toward_zero
char16_t (since C++11) | std::round_toward_zero
char32_t (since C++11) | 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 (since C++11) | std::round_toward_zero
unsigned long long (since C++11) | 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-754 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
.

Run this code

    #include <iostream>
    #include <limits>

    auto print(std::float_round_style frs)
    {
        switch (frs)
        {
            case std::round_indeterminate:
                return "Rounding style cannot be determined";
            case std::round_toward_zero:
                return "Rounding toward zero";
            case std::round_to_nearest:
                return "Rounding toward nearest representable value";
            case std::round_toward_infinity:
                return "Rounding toward positive infinity";
            case std::round_toward_neg_infinity:
                return "Rounding toward negative infinity";
        }
        return "unknown round style";
    }

    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'
                  << print(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
    Rounding toward nearest representable value

### See also

float_round_style | indicates floating-point rounding modes (enum)

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