CODEWITHSUNDEEP
c++undefined
user954004
user954004

Reputation: 99

How to check for undefined value of a double?

I am trying to figure out a way to check for a undefined value of a slope in which case it would be vertical. I have tried using NULL but that doesn't seem to work.

double Point::Slope(Point &p2)
{
   double slop = 0;
   slop = (y - p2.y) / (x - p2.x);

   if (slop == NULL)
   {
      slop = 10e100;
   }

   return slop;   
}

Upvotes: 1

Views: 6693

Answers (3)

Walter
Walter

Reputation: 45474

If you mean nan ('not a number') with "undefined", you should avoid computing one in the first place, i.e. by checking that the denominator of a '/' operation is not zero. Second, you can always check for nan by

#include <cmath>
bool std::isnan(x);   // since C++11
bool isnan(x);        // pre C++11, from the C math library, defined as macro

see the man pages, or cppreference.

Upvotes: 3

Gyan
Gyan

Reputation: 12410

I'd recommend avoiding the divide-by-zero all together (by the way... why don't you call it slope instead of slop?):

double Point::Slope(Point&p2)
{
    double slope = 0;
    double xDelta = x - p2.x;
    double yDelta = y - p2.y;

    if (xDelta != 0)
    {
        slope = yDelta / xDelta;
    }

    return slope;   
}

Upvotes: 0

Clement Bellot
Clement Bellot

Reputation: 841

In C++, NULL == 0. This is not what you seek.

Maybe this may help you : http://www.gnu.org/s/hello/manual/libc/Infinity-and-NaN.html

Try the isnan(float) function.

Upvotes: 1

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