std::signbit

 

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Common mathematical functions

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abs(int)labsllabsimaxabs (C++11) abs(float)fabs divldivlldivimaxdiv (C++11) fmod	remainder (C++11) remquo (C++11) fma (C++11) fmax (C++11) fmin (C++11) fdim (C++11) nannanfnanl (C++11)(C++11)(C++11)
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Classification/Comparison
fpclassify (C++11) isfinite (C++11) isinf (C++11) isnan (C++11) isnormal (C++11) signbit (C++11)	isgreater (C++11) isgreaterequal (C++11) isless (C++11) islessequal (C++11) islessgreater (C++11) isunordered (C++11)
Macro constants
HUGE_VALFHUGE_VALHUGE_VALL (C++11)(C++11) INFINITY (C++11) NAN (C++11) math_errhandlingMATH_ERRNOMATH_ERREXCEPT (C++11)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C++11)(C++11)(C++11)(C++11)(C++11)

 

Defined in header <cmath>
bool signbit( float arg );	(1)	(since C++11)
bool signbit( double arg );	(2)	(since C++11)
bool signbit( long double arg );	(3)	(since C++11)
bool signbit( IntegralType arg );	(4)	(since C++11)

1-3) Determines if the given floating point number arg is negative.

4) A set of overloads or a function template accepting the arg argument of any integral type. Equivalent to (2) (the argument is cast to double).

Parameters

arg

-

floating point value

Return value

true if arg is negative, false otherwise

Notes

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

Examples

Run this code

#include <iostream>
#include <cmath>
 
int main()
{
    std::cout << std::boolalpha
              << "signbit(+0.0) = " << std::signbit(+0.0) << '\n'
              << "signbit(-0.0) = " << std::signbit(-0.0) << '\n';
}

Output:

signbit(+0.0) = false
signbit(-0.0) = true

See also

abs(float)fabsfabsffabsl (C++11)(C++11)	absolute value of a floating point value (|x|) (function)
copysigncopysignfcopysignl (C++11)(C++11)(C++11)	copies the sign of a floating point value (function)
C documentation for signbit