std::numeri...round_style(3) C++ Standard Libary std::numeri...round_style(3) NAME std::numeric_limits::round_style - std::numeric_limits::round_style Synopsis 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 ex- actly repesentable values of T is stored in an object of that type. Standard specializations T value of std::numeric_lim- its<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 round- ing 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) http://cppreference.com 2024.06.10 std::numeri...round_style(3)
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