lround man page

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.

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.

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.

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>

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2013 IEEE/The Open Group POSIX Programmer's Manual