```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.1‐2008 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| + |v| + ... + |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.
```

## SEE ALSO         top

```       isnan(3p)

The Base Definitions volume of POSIX.1‐2008, math.h(0p)
```

## COPYRIGHT         top

```       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 .

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/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                            FABS(3P)
```

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