The Open Group Base Specifications Issue 7

IEEE Std 1003.1-2008

Copyright © 2001-2008 The IEEE and The Open Group

#### NAME

round, roundf, roundl - round to the nearest integer value in a floating-point format

#### SYNOPSIS

`#include <math.h>`

double round(double *x*`);`

float roundf(float *x*`);`

long double roundl(long double *x*`);`

#### DESCRIPTION

^{[CX]} The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the
requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C
standard.

These functions shall round their argument to the nearest integer value in floating-point format, rounding halfway cases away
from zero, regardless of the current rounding direction.

An application wishing to check for error situations should set *errno* to zero and call
*feclearexcept*(FE_ALL_EXCEPT) before calling these functions. On return, if *errno* is non-zero or
*fetestexcept*(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

#### RETURN VALUE

Upon successful completion, these functions shall return the rounded integer value.

^{[MX]} If
*x* is NaN, a NaN shall be returned.

If *x* is ±0 or ±Inf, *x* shall be returned.

^{[XSI]}
If the correct value would cause overflow, a range error shall occur and *round*(), *roundf*(), and *roundl*() shall
return the value of the macro ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (with the same sign as *x*),
respectively.

#### ERRORS

These functions may fail if:

- Range Error
^{[XSI]}
The result overflows.
If the integer expression (*math_errhandling* & MATH_ERRNO) is non-zero, then *errno* shall be set to [ERANGE]. If
the integer expression (*math_errhandling* & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall
be raised.

*The following sections are informative.*

#### EXAMPLES

None.

#### APPLICATION USAGE

On error, the expressions (*math_errhandling* & MATH_ERRNO) and (*math_errhandling* & MATH_ERREXCEPT) are
independent of each other, but at least one of them must be non-zero.

#### RATIONALE

None.

#### FUTURE DIRECTIONS

None.

#### SEE ALSO

*feclearexcept* , *fetestexcept*

XBD *Treatment of Error Conditions for Mathematical Functions* , *<math.h>*

#### CHANGE HISTORY

First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.

*End of informative text.*

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