How to correctly and standardly compare floats?

Question

Every time I start a new project and when I need to compare some float or double variables I write the code like this one:

if (fabs(prev.min[i] - cur->min         


        

Answer 1

You can use std::nextafter for testing two double with the smallest epsilon on a value (or a factor of the smallest epsilon).

bool nearly_equal(double a, double b)
{
  return std::nextafter(a, std::numeric_limits::lowest()) <= b
    && std::nextafter(a, std::numeric_limits::max()) >= b;
}

bool nearly_equal(double a, double b, int factor /* a factor of epsilon */)
{
  double min_a = a - (a - std::nextafter(a, std::numeric_limits::lowest())) * factor;
  double max_a = a + (std::nextafter(a, std::numeric_limits::max()) - a) * factor;

  return min_a <= b && max_a >= b;
}