lround(), lroundf(), lroundl()

Updated: April 19, 2023

Round a floating-point number to the nearest integer value

Synopsis:

#include <math.h>

long int lround( double x );

long int lroundf( float x );

long int lroundl( long double x );

Arguments:

x
The number that you want to round.

Library:

libm
The general-purpose math library.
libm-sve
(QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

Description:

The lround(), lroundf(), and lroundl() functions round a floating-point number to the nearest integer value, rounding halfway cases away from zero, regardless of the current rounding direction.

To check for error situations, use feclearexcept() and fetestexcept(). For example:

Returns:

The rounded integer value.

If: These functions return: Errors:
x is ±Inf An unspecified value FE_INVALID
x is NaN An unspecified value FE_INVALID
The correct value is too large to represent as a long An unspecified value FE_INVALID

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

Classification:

C11, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes