IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)

Copyright © 2001-2018 IEEE and The Open Group

lround, lroundf, lroundl - round to nearest integer value

#include <math.h>

long lround(doublex);

long lroundf(floatx);

long lroundl(long doublex);

^{[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.1-2017 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

errnoto zero and callfeclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions shall return the rounded integer value.

^{[MX]}Ifxis NaN, a domain error shall occur and an unspecified value is returned.If

xis +Inf, a domain error shall occur and an unspecified value is returned.If

xis -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.^{[MX]}On systems that support the IEC 60559 Floating-Point option, a domain shall occur; otherwise, a^{[CX]}domain error may occur.If the correct value is negative and too large to represent as a

long, an unspecified value shall be returned.^{[MX]}On systems that support the IEC 60559 Floating-Point option, a domain shall occur; otherwise, a^{[CX]}domain error may occur.

These functions shall fail if:

- Domain Error
^{[MX]}Thexargument 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, thenerrnoshall 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, thenerrnoshall be set to [EDOM]. If the integer expression (math_errhandling& MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

None.

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.

These functions differ from the

lrint() functions in the default rounding direction, with thelround() 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.

None.

feclearexcept,fetestexcept,llroundXBD

Treatment of Error Conditions for Mathematical Functions,<math.h>

First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.

ISO/IEC 9899:1999 standard, Technical Corrigendum 2 #54 (SD5-XSH-ERN-78) is applied.

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