fegetround, fesetround

Gets or sets the current floating-point rounding mode.

Syntax

int fegetround(void);

int fesetround(
   int round_mode
);

Parameters

round_mode
The rounding mode to set, as one of the floating-point rounding macros. If the value isn't equal to one of the floating-point rounding macros, the rounding mode isn't changed.

Return value

On success, fegetround returns the rounding mode as one of the floating point rounding macro values. It returns a negative value if the current rounding mode can't be determined.

On success, fesetround returns 0. Otherwise, a non-zero value is returned.

Remarks

Floating-point operations can use one of several rounding modes. These modes control which direction the results of floating-point operations are rounded toward when the results are stored. Here are the names and behaviors of the floating-point rounding macros defined in <fenv.h>:

Macro	Description
FE_DOWNWARD	Round towards negative infinity.
FE_TONEAREST	Round towards the nearest.
FE_TOWARDZERO	Round towards zero.
FE_UPWARD	Round towards positive infinity.

The default behavior of FE_TONEAREST is to round results midway between representable values toward the nearest value with an even (0) least significant bit.

The current rounding mode affects these operations:

• String conversions.

• The results of floating-point arithmetic operators outside of constant expressions.

• The library rounding functions, such as rint and nearbyint.

• Return values from standard library mathematical functions.

The current rounding mode doesn't affect these operations:

• The trunc, ceil, floor, and lround library functions.

• Floating-point to integer implicit casts and conversions, which always round towards zero.

• The results of floating-point arithmetic operators in constant expressions, which always round to the nearest value.

To use these functions, you must turn off floating-point optimizations that could prevent access by using the #pragma fenv_access(on) directive prior to the call. For more information, see fenv_access.

Requirements

Function	C header	C++ header
fegetround, fesetround	<fenv.h>	<cfenv>

For more compatibility information, see Compatibility.

See also

Alphabetical function reference
nearbyint, nearbyintf, nearbyintl
rint, rintf, rintl
lrint, lrintf, lrintl, llrint, llrintf, llrintl