Re: Interesting behavior of double.NaN

Reminds me very much of how in SQL NULL is equal to NULL, nor is it
not-equal to a number. Thanks for sharing this!

Sam

On Mon, Mar 23, 2009 at 9:40 AM, Brink, Paul ten <[email protected]
> wrote:

> Hello,
>
> After a long search I finally found why my program is not working properly:
> double.NaN != double.NaN
>
> You can try this for yourself in the Quick Watch window.
>
> This interesting behavior is by design. From the documentation:
>
> ----------------------------
> Double.NaN Field
>
> Represents a value that is not a number (NaN). This field is constant.
>
> Use IsNaN<http://msdn.microsoft.com/en-us/library/system.double.isnan.aspx>
> to determine whether a value is not a number. It is not possible to
> determine whether a value is not a number by comparing it to another value
> equal to NaN.
> ----------------------------
>
> Hm, a constant that is not equal to itself. Interesting...
>
> But it is very dangerous:
>
> If (width != this.Width)
>
> returns true if both are double.NaN
>
> Don't say Microsoft did not warn you...     ;-)
>
> I now use:
>
> private bool DoubleEquals(double d1, double d2)
> {
>    bool result = false;
>
>    bool isNaN1 = double.IsNaN(d1);
>    bool isNaN2 = double.IsNaN(d2);
>
>    if (isNaN1)
>    {
>        result  = isNaN2;
>    }
>    else
>    {
>        if (! isNaN2)
>        {
>            result = (d1 == d2);
>        }
>    }
>
>    return result;
> }
>
> Paul ten Brink
> [email protected]
>
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