### NAME

signbit - test sign of a real floating-point number

### SYNOPSIS

**#include <math.h>**

**int signbit(***x***);**

Link with *-lm*.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

**signbit**(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or
*cc -std=c99*

### DESCRIPTION

**signbit**() is a generic macro which can work on all real floating-point types.
It returns a non-zero value if the value of
*x* has its sign bit set.

This is not the same as
*x < 0.0*, because IEEE 754 floating point allows zero to be signed.
The comparison
*-0.0 < 0.0* is false, but
*signbit(-0.0)* will return a non-zero value.

NaNs and infinities have a sign bit.

### RETURN VALUE

The
**signbit**() macro returns non-zero if the sign of
*x* is negative; otherwise it returns zero.

### ERRORS

No errors occur.

### CONFORMING TO

C99, POSIX.1-2001. This function is defined in IEC 559 (and the appendix with recommended functions in IEEE 754/IEEE 854).

### SEE ALSO

### COLOPHON

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