# fabs(3p) — Linux manual page

```FABS(3P)                POSIX Programmer's Manual               FABS(3P)
```

## PROLOG         top

```       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         top

```       fabs, fabsf, fabsl — absolute value function
```

## SYNOPSIS         top

```       #include <math.h>

double fabs(double x);
float fabsf(float x);
long double fabsl(long double x);
```

## DESCRIPTION         top

```       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.1‐2017 defers to the ISO C standard.

These functions shall compute the absolute value of their
argument x,|x|.
```

## RETURN VALUE         top

```       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         top

```       No errors are defined.

The following sections are informative.
```

## EXAMPLES         top

```   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;
}
```

## APPLICATION USAGE         top

```       None.
```

## RATIONALE         top

```       None.
```

## FUTURE DIRECTIONS         top

```       None.
```

```       isnan(3p)

The Base Definitions volume of POSIX.1‐2017, math.h(0p)
```

```       Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, 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 .

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/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                          FABS(3P)
```