I'm wondering what ? means in C# ?
I'm seeing things like: DateTime? or int?. I suppose this is specific to C# 4.0?
I can't look for it in Google because I don't know the name of this thing.
The problem is I'm using DateTime and I have a lot of cast errors (from DateTime to DateTime?).
Thank you
The ? is a nullable value type.
You can use the ?? operator to mix it with value types:
const int DefaultValue = -1;
// get a result that may be an integer, or may be null
int? myval = GetOptionalIdFromDB();
// the value after ?? is used if myval is null
int nonNullable = myval ?? DefaultValue;
The nullable type can be compared to null, so the above is shorthand for:
if( myval != null ) {
nonNullable = myval.Value;
} else {
nonNullable = DefaultValue;
}
But I prefer ??