LROUND
Section: POSIX Programmer's Manual (3P)
Updated: 2013
Page Index
PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
lround,
lroundf,
lroundl
 round to nearest integer value
SYNOPSIS
#include <math.h>
long lround(double x);
long lroundf(float x);
long lroundl(long double x);
DESCRIPTION
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.12008 defers to the ISO C standard.
These functions shall round their argument to the nearest integer
value, 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 nonzero or fetestexcept(FE_INVALID  FE_DIVBYZERO 
FE_OVERFLOW  FE_UNDERFLOW) is nonzero, an error has occurred.
RETURN VALUE
Upon successful completion, these functions shall return the rounded
integer value.
If
x
is NaN, a domain error shall occur and an unspecified value is
returned.
If
x
is +Inf, a domain error shall occur and an unspecified value is
returned.
If
x
is Inf, a domain error shall occur and an unspecified value is
returned.
If the correct value is positive and too large to represent as a
long,
an unspecified value shall be returned.
On systems that support the IEC 60559 FloatingPoint option, a domain
shall occur;
otherwise, a
domain
error may occur.
If the correct value is negative and too large to represent as a
long,
an unspecified value shall be returned.
On systems that support the IEC 60559 FloatingPoint option, a domain
shall occur;
otherwise, a
domain
error may occur.
ERRORS
These functions shall fail if:
 Domain Error

The
x
argument is NaN or ±Inf, or the correct value is not representable
as an integer.

If the integer expression (math_errhandling & MATH_ERRNO) is
nonzero, then
errno
shall be set to
[EDOM].
If the integer expression (math_errhandling & MATH_ERREXCEPT) is
nonzero, then the invalid floatingpoint exception shall be raised.
These functions may fail if:
 Domain Error

The correct value is not representable as an integer.

If the integer expression (math_errhandling & MATH_ERRNO) is
nonzero, then
errno
shall be set to
[EDOM].
If the integer expression (math_errhandling & MATH_ERREXCEPT) is
nonzero, then the invalid floatingpoint 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 nonzero.
RATIONALE
These functions differ from the
lrint()
functions in the default rounding direction, with the
lround()
functions rounding halfway cases away from zero and needing not to
raise the inexact floatingpoint exception for noninteger arguments
that round to within the range of the return type.
FUTURE DIRECTIONS
None.
SEE ALSO
feclearexcept(),
fetestexcept(),
llround()
The Base Definitions volume of POSIX.12008,
Section 4.19, Treatment of Error Conditions for Mathematical Functions,
<math.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
 Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.12008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/manpages/reporting_bugs.html .