# fabs man page

## 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.

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.1‐2008 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 1-Norm of a Floating-Point Vector

This example shows the use of *fabs*() to compute the 1-norm of a vector defined as follows:

`norm1(v) = |v[0]| + |v[1]| + ... + |v[n-1]|`

where |*x*| denotes the absolute value of *x*, *n* denotes the vector's dimension *v*[*i*] denotes the *i*-th component of *v* (0≤*i*<*n*).

```
#include <math.h>
double
norm1(const double v[], const int n)
{
int i;
double n1_v; /* 1-norm of v */
n1_v = 0;
for (i=0; i<n; i++) {
n1_v += fabs (v[i]);
}
return n1_v;
}
```

## See Also

*isnan()*

The Base Definitions volume of POSIX.1‐2008, **<math.h>**

## Copyright

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .