问题
I have 2 nullable doubles, an expected value and an actual value (let's call them value and valueExpected). A percentage is found using 100 * (value / valueExpected). However, if valueExpected is zero, it returns NaN. Everything good so far.
Now, what do I do if I need to check the value, to see if it is NaN? Normally one could use:
if (!Double.IsNaN(myDouble))
But this doesn't work with nullable values (IsNaN only works with non-nullable variables). I have changed my code to do the check (valueExpected == 0), but I'm still curious - is there any way to check for a nullable NaN?
Edit: When I say the code doesn't work, I mean it won't compile. Testing for null first doesn't work.
回答1:
With all Nullable<T> instances, you first check the bool HasValue property, and then you can access the T Value property.
double? d = 0.0; // Shorthand for Nullable<double>
if (d.HasValue && !Double.IsNaN(d.Value)) {
double val = d.Value;
// val is a non-null, non-NaN double.
}
回答2:
You can also use
if (!Double.IsNaN(myDouble ?? 0.0))
The value in the inner-most parenthesis is either the myDouble
(with its Nullable<>
wrapping removed) if that is non-null, or just 0.0
if myDouble
is null
. Se ?? Operator (C#).
回答3:
I had the same issue and I solved it with casting the double? with double
double.IsNaN((double)myDouble)
this will return true if NaN and false if not
来源:https://stackoverflow.com/questions/13597277/nullable-double-nan-comparison-in-c-sharp