std::signbit (3) - Linux Manuals

std::signbit: std::signbit

NAME

std::signbit - std::signbit

Synopsis

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