---
name: "signbit"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
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

Standard C Library (libc, -lc)

## SYNOPSIS

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

*int*\

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

## DESCRIPTION

The **signbit**() macro takes an argument of *x*. It returns non-zero if the value of the argument's 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”).