FABS
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
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.
NAME
fabs,
fabsf,
fabsl
 absolute value function
SYNOPSIS
#include <math.h>
double fabs(double x);
float fabsf(float x);
long double fabsl(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.12017 defers to the ISO C standard.
These functions shall compute the absolute value of their argument
x,x.
RETURN VALUE
Upon successful completion, these functions shall return the absolute
value of
x.
If
x
is NaN, a NaN shall be returned.
If
x
is ±0, +0 shall be returned.
If
x
is ±Inf, +Inf shall be returned.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
Computing the 1Norm of a FloatingPoint Vector
This example shows the use of
fabs()
to compute the 1norm of a vector defined as follows:

norm1(v) = v[0] + v[1] + ... + v[n1]
where x denotes the absolute value of x, n denotes
the vector's dimension v[i] denotes the
ith
component of v (0≤i<n).

#include <math.h>
double
norm1(const double v[], const int n)
{
int i;
double n1_v; /* 1norm of v */
n1_v = 0;
for (i=0; i<n; i++) {
n1_v += fabs (v[i]);
}
return n1_v;
}
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
isnan()
The Base Definitions volume of POSIX.12017,
<math.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.12017, Standard for Information Technology
 Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/manpages/reporting_bugs.html .