std::fegetround, std::fesetround

 

C++

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Floating-point environment

feclearexcept (C++11)

fetestexcept (C++11)

feraiseexcept (C++11)

fegetexceptflag fesetexceptflag (C++11) (C++11)

fegetround (C++11)

fesetround (C++11)

fegetenv (C++11)

feholdexcept (C++11)

fesetenv (C++11)

feupdateenv (C++11)

FE_ALL_EXCEPT FE_DIVBYZERO FE_INEXACT FE_INVALID FE_OVERFLOW FE_UNDERFLOW (C++11)

FE_DOWNWARD FE_TONEAREST FE_TOWARDZERO FE_UPWARD (C++11)

FE_DFL_ENV (C++11)

 

Defined in header <cfenv>
int fesetround( int round )	(1)	(since C++11)
int fegetround()	(2)	(since C++11)

1) Attempts to establish the floating-point rounding direction equal to the argument 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

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

See also

nearbyint (C++11)	nearest integer using current rounding mode (function)
rint lrint llrint (C++11) (C++11) (C++11)	nearest integer using current rounding mode with exception if the result differs (function)