fabs(), fabsf(), fabsl()

Updated: May 06, 2022

Compute the absolute value of a double number

Synopsis:

#include <math.h>

double fabs( double x );

float fabsf( float x );

long double fabsl( long double x );

Arguments:

x
The number you want the absolute value of.

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 fabs(), fabsf(), and fabsl() functions compute the absolute value of x.

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

Returns:

The absolute value of x.

If x is: These functions return: Errors:
±0.0 0.0
±Inf Inf
NaN NaN

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

Examples:

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

int main( void )
{
    printf( "%f %f\n", fabs(.5), fabs(-.5) );
    return EXIT_SUCCESS;
}

produces the output:

0.500000 0.500000

Classification:

C11, POSIX 1003.1

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