---
name: "signbit"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/signbit"
---

# signbit(3)

determine whether a floating-point number's sign is negative

## NAME

**signbit** – determine whether a floating-point number's sign is negative

## LIBRARY

Math Library (libm, -lm)

## SYNOPSIS

**#include \<math.h\>**

*int*\

**signbit**(*real-floating x*);

## DESCRIPTION

The **signbit**() macro takes an argument of *x* and returns non-zero if the value of its sign is negative, otherwise 0.

## SEE ALSO

[fpclassify(3)](/fpclassify/3.md), [math(3)](/math/3.md)

## STANDARDS

The **signbit**() macro conforms to ISO/IEC 9899:1999 (“ISO C99”).

## HISTORY

The **signbit**() macro was added in FreeBSD 5.1.