Std::fegetround,std::fesetround (3) Linux Manual Page

std::fegetround,std::fesetround – std::fegetround,std::fesetround

Synopsis

Defined in header <cfenv>
int fesetround( int round ) (1) (since C++11)
int fegetround() (2) (since C++11)
Manages the floating-point rounding direction.
1) Attempts to establish the floating-point rounding direction equal to the argument round, which is expected to be one of the floating_point_rounding_macros.
2) Returns the value of the floating_point_rounding_macro that corresponds to the current rounding direction.

Parameters

round – rounding direction, one of floating_point_rounding_macros

Return value

1) 0 on success, non-zero otherwise.
2) the floating_point_rounding_macro describing the current rounding direction or a negative value if the direction cannot be determined

Notes

The current rounding mode, reflecting the effects of the most recent fesetround, can also be queried with FLT_ROUNDS
See floating-point_rounding_macros for the effects of rounding.

Example

// Run this code

#include <cmath>

#include <cfenv>

#include <iostream>
int main()

{
#pragma STDC FENV_ACCESS ON
    std::fesetround(FE_DOWNWARD);
    std::cout << "rounding using FE_DOWNWARD: \n"
              << std::fixed
              << " 12.0 ->  " << std::nearbyint(12.0) << '\n'
              << " 12.1 ->  " << std::nearbyint(12.1) << '\n'
              << "-12.1 -> " << std::nearbyint(-12.1) << '\n'
              << " 12.5 ->  " << std::nearbyint(12.5) << '\n'
              << " 12.9 ->  " << std::nearbyint(12.9) << '\n'
              << "-12.9 -> " << std::nearbyint(-12.9) << '\n'
              << " 13.0 ->  " << std::nearbyint(13.0) << '\n';
    std::fesetround(FE_TONEAREST);
    std::cout << "rounding using FE_TONEAREST: \n"
              << " 12.0 ->  " << std::nearbyint(12.0) << '\n'
              << " 12.1 ->  " << std::nearbyint(12.1) << '\n'
              << "-12.1 -> " << std::nearbyint(-12.1) << '\n'
              << " 12.5 ->  " << std::nearbyint(12.5) << '\n'
              << " 12.9 ->  " << std::nearbyint(12.9) << '\n'
              << "-12.9 -> " << std::nearbyint(-12.9) << '\n'
              << " 13.0 ->  " << std::nearbyint(13.0) << '\n';
}

Output:

  rounding using FE_DOWNWARD:
   12.0 -> 12.000000
   12.1 -> 12.000000
  -12.1 -> -13.000000
   12.5 -> 12.000000
   12.9 -> 12.000000
  -12.9 -> -13.000000
   13.0 -> 13.000000
  rounding using FE_TONEAREST:
   12.0 -> 12.000000
   12.1 -> 12.000000
  -12.1 -> -12.000000
   12.5 -> 12.000000
   12.9 -> 13.000000
  -12.9 -> -13.000000
   13.0 -> 13.000000

std::fegetround,std::fesetround (3) Linux Manual Page