---
name: "fabs"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/fabs"
---

# fabs(3)

absolute value of floating-point number

## NAME

fabs, fabsf, fabsl - absolute value of floating-point number

## LIBRARY

Math library (*libm*, *-lm*)

## SYNOPSIS

```
#include <math.h>
```

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

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**fabsf**(), **fabsl**():

```
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

## DESCRIPTION

These functions return the absolute value of the floating-point number *x*.

## RETURN VALUE

These functions return the absolute value of *x*.

If *x* is a NaN, a NaN is returned.

If *x* is -0, +0 is returned.

If *x* is negative infinity or positive infinity, positive infinity is returned.

## ERRORS

No errors occur.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **fabs**(), **fabsf**(), **fabsl**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

C99, POSIX.1-2001.

The variant returning *double* also conforms to SVr4, 4.3BSD, C89.

## SEE ALSO

[**abs**(3)](/abs/3.md), [**cabs**(3)](/cabs/3.md), [**ceil**(3)](/ceil/3.md), [**floor**(3)](/floor/3.md), [**labs**(3)](/labs/3.md), [**rint**(3)](/rint/3.md)