std::signbit

< cpp‎ | numeric‎ | math
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.

Example

#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

(C++11)(C++11)
 absolute value of a floating point value (|x|)
(function)
(C++11)(C++11)(C++11)
 copies the sign of a floating point value
(function)