NAME

std::signbit - std::signbit

Synopsis

Defined in header <cmath>
bool signbit( float arg ); (1) (since C++11)
(constexpr since C++23)
bool signbit( double arg ); (2) (since C++11)
(constexpr since C++23)
bool signbit( long double arg ); (3) (since C++11)
(constexpr since C++23)
bool signbit( IntegralType arg ); (4) (since C++11)
(constexpr since C++23)

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.

Example

// 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)
fabs
fabsf absolute value of a floating point value (\(\small{|x|}\)|x|)
fabsl (function)
(C++11)
(C++11)
copysign
copysignf
copysignl copies the sign of a floating point value
(C++11) (function)
(C++11)
(C++11)