signbit - test sign of a real floating-point number

```
#include <math.h>
int signbit(x);
Link with -lm.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
signbit():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
```

signbit() is a generic macro which can work on all real floating-point types. It returns a nonzero 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 nonzero value.

NaNs and infinities have a sign bit.

The signbit() macro returns nonzero if the sign of `x`

is negative; otherwise it returns zero.

No errors occur.

For an explanation of the terms used in this section, see attributes(7).

Interface | Attribute | Value |

signbit() | Thread safety | MT-Safe |

POSIX.1-2001, POSIX.1-2008, C99. This function is defined in IEC 559 (and the appendix with recommended functions in IEEE 754/IEEE 854).

copysign(3)

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