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.1-2024 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.

[MX] These functions may raise the inexact floating-point exception for finite non-integer arguments.

RETURN VALUE

Upon successful completion, these functions shall return the rounded integer value. [MX] The result shall have the same sign as x.

[MX] If x is NaN, a NaN shall be returned.

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

ERRORS

No errors are defined.

The following sections are informative.

EXAMPLES

None.

APPLICATION USAGE

The integral value returned by these functions need not be expressible as an intmax_t. The return value should be tested before assigning it to an integer type to avoid the undefined results of an integer overflow.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

feclearexcept(3), fetestexcept(3)

XBD V1_chap04(7), <math.h>

CHANGE HISTORY

First released in Issue 6. Derived from the ISO/IEC 9899:1999 (“ISO C99”) standard.

Issue 7

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0520 [346] is applied.

Issue 8

Austin Group Defect 1302 is applied, aligning these functions with the ISO/IEC 9899:2018 standard.

End of informative text.