Question

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What does “DateTime?” mean in C#?
What does the ? mean after a type?

I had a function declaration including a questionmark after the datatype like:

private TimeSpan? sometime()
{

}

What does this mean?

Answer 1

TimeSpan? is shorthand for System.Nullable<TimeSpan>.

A TimeSpan is a value type, which cannot take a null value. By wrapping it in a System.Nullable<> it can be null. Without that ? it would be illegal to return null from the function.