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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
lrint, lrintf, lrintl — round to nearest integer value using current rounding direction
SYNOPSIS
#include <math.h> long lrint(double x); long lrintf(float x); long lrintl(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.1‐2017 defers to the ISO C standard.
These functions shall round their argument to the nearest integer value, rounding according to 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 error 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 error 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 provide floating-to-integer conversions. They round according to the current rounding
direction. If the rounded value is outside the range of the return type, the numeric result is
unspecified and the invalid floating-point exception is raised. When they raise no other floating-point
exception and the result differs from the argument, they raise the inexact floating-point exception.
FUTURE DIRECTIONS
None.
SEE ALSO
feclearexcept(), fetestexcept(), llrint()
The Base Definitions volume of POSIX.1‐2017, Section 4.20, Treatment of Error Conditions for Mathematical
Functions, <math.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/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 .