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std::fegetround, std::fesetround

From cppreference.com
< cpp‎ | numeric‎ | fenv
 
 
 
Floating-point environment
Functions
fegetroundfesetround
(C++11)(C++11)
(C++11)(C++11)
Macro constants
(C++11)
 
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.

Contents

[edit] Parameters

round - rounding direction, one of floating point rounding macros

[edit] 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

[edit] 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.

[edit] Example

#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

[edit] See also

(C++11)(C++11)(C++11)
nearest integer using current rounding mode
(function) [edit]
(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)
nearest integer using current rounding mode with
exception if the result differs
(function) [edit]
C documentation for fegetround, fesetround