The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Copyright © 2001-2013 The IEEE and The Open Group

#### 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

> [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.1-2008 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.

> [MX] 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. [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.

#### ERRORS

> These functions shall fail if:

> Domain Error
>   [MX] 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

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

#### CHANGE HISTORY

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

#### Issue 7

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

End of informative text.

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