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.1‐2008 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 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.

       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 Floating-Point  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 Floating-Point  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  non-zero,  then
                   errno  shall  be set to [EDOM].  If the integer expression (math_errhandling &
                   MATH_ERREXCEPT) is non-zero, then the invalid floating-point  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 non-zero, then
                   errno shall be set to [EDOM].  If the integer expression  (math_errhandling  &
                   MATH_ERREXCEPT)  is  non-zero, then the invalid 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

       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  floating-point exception for non-integer 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.1‐2008, 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.1-2008  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/man-pages/reporting_bugs.html .