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signbit

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< c‎ | numeric‎ | math

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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.

Contents

1 Parameters
2 Return value
3 Notes
4 Example
5 References
6 See also

[edit] Parameters

arg - floating-point value

[edit] Return value

Nonzero integral value if arg is negative, 0 otherwise.

[edit] 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.

[edit] Example

Run this code

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

[edit] References

C23 standard (ISO/IEC 9899:2024):

7.12.3.6 The signbit macro (p: TBD)

C17 standard (ISO/IEC 9899:2018):

7.12.3.6 The signbit macro (p: TBD)

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)

[edit] See also

(C99)(C99)

computes absolute value of a floating-point value (\(\small{|x|}\)|x|)
(function) [edit]

copysigncopysignfcopysignl

(C99)(C99)(C99)

produces a value with the magnitude of a given value and the sign of another given value
(function) [edit]

C++ documentation for signbit

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