# signbit

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< c‎ | numeric‎ | math

Defined in header `<math.h>` |  |
#define signbit(arg) /* implementation defined */ |  | (since C99)

Determines if the given floating point number `arg` is negative. The macro returns an integral value.

### Parameters

arg | - | floating point value

### Return value

Nonzero integral value if `arg` is negative, ​0​ otherwise.

### Notes

This macro detects the sign bit of zeroes, infinities, and NaNs. Along with copysign, this macro is one of the only two portable ways to examine the sign of a NaN.

### Example

Run this code

    #include <stdio.h>
    #include <math.h>

    int main(void)
    {
        printf("signbit(+0.0) = %d\n", signbit(+0.0));
        printf("signbit(-0.0) = %d\n", signbit(-0.0));
    }

Possible output:

    signbit(+0.0) = 0
    signbit(-0.0) = 128

### References

- C11 standard (ISO/IEC 9899:2011):

  - 7.12.3.6 The signbit macro (p: 237)

- C99 standard (ISO/IEC 9899:1999):

  - 7.12.3.6 The signbit macro (p: 218)

### See also

fabs fabsf fabsl (C99)(C99) | computes absolute value of a floating-point value (|x|) (function)
copysign copysignf copysignl (C99)(C99)(C99) | produces a value with the magnitude of a given value and the sign of another given value (function)
C++ documentation for signbit

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