function
<cfenv>
fesetround
int fesetround (int rdir);
Set rounding direction mode
Sets rdir as the current rounding direction mode for the floating point environment.
Programs calling this function shall ensure that pragma FENV_ACCESS is enabled for the call.
Parameters
- rdir
- One of the values defined as rounding direction mode:
Certain library implementations may support additional floating-point rounding directions values (with their corresponding macros also beginning with FE_).
Libraries may define in
<fenv.h> only the macro values above they support (the others may not be defined).
At least all of the above macro values are defined in
<cfenv>.
If an int value other than those defined by these macros is passed, the function does not change the rounding direction mode and returns a non-zero value.
Return Value
Zero, if the requested rounding direction was successfully set.
Otherwise, a non-zero value.
Example
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/* fesetround example */
#include <stdio.h> /* printf */
#include <fenv.h> /* fesetround, FE_* */
#include <math.h> /* rint */
#pragma STDC FENV_ACCESS on
int main ()
{
printf ("rounding -3.8:\n");
fesetround(FE_DOWNWARD);
printf ("FE_DOWNWARD: %.1f\n", rint(-3.8));
fesetround(FE_TONEAREST);
printf ("FE_TONEAREST: %.1f\n", rint(-3.8));
fesetround(FE_TOWARDZERO);
printf ("FE_TOWARDZERO: %.1f\n", rint(-3.8));
fesetround(FE_UPWARD);
printf ("FE_UPWARD: %.1f\n", rint(-3.8));
return 0;
}
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Possible output:
rounding -3.8:
FE_DOWNWARD: -4.0
FE_TONEAREST: -4.0
FE_TOWARDZERO: -3.0
FE_UPWARD: -3.0
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Data races
Each thread maintains a separate floating-point environment with its own state. Spawning a new thread copies the current state. [This applies to C11 and C++11 implementations]
Exceptions
No-throw guarantee: this function never throws exceptions.
See also
- fegetround
- Get rounding direction mode (function)
- fesetenv
- Set floating-point environment (function)
- rint
- Round to integral value (function)