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

[edit]Standard specializations

[edit]Notes

These values are constants, and do not reflect the changes to the rounding made bystd::fesetround. The changed values may be obtained fromFLT_ROUNDS orstd::fegetround.

[edit]Example

The decimal value0.1 cannot be represented by a binary floating-point type. When stored in an IEEE-754double, it falls between0x1.9999999999999*2-4
and0x1.999999999999a*2-4
. Rounding to nearest representable value results in0x1.999999999999a*2-4
.

Similarly, the decimal value0.3, which is between0x1.3333333333333*2-2
and0x1.3333333333334*2-2
is rounded to nearest and is stored as0x1.3333333333333*2-2
.

#include <iostream>#include <limits> auto print(std::float_round_style frs){switch(frs){casestd::round_indeterminate:return"Rounding style cannot be determined";casestd::round_toward_zero:return"Rounding toward zero";casestd::round_to_nearest:return"Rounding toward nearest representable value";casestd::round_toward_infinity:return"Rounding toward positive infinity";casestd::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';}

The decimal 0.1 is stored in a double as 0x1.999999999999ap-4The decimal 0.3 is stored in a double as 0x1.3333333333333p-2Rounding toward nearest representable value

[edit]See also

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