如何在 C# 中将可空修饰符作为输出参数传递

Question

Suppose I declare an int with a nullable modifier and I want to pass it as an out parameter to a function. How would I do that?

int? count = null;
if(int.TryParse(System.Console.ReadLine(), out count /* illegal */))
...

Answer 1

int? is shorthand for System.Nullable<int> . Adding the ? to the end of a value type actually declares a different type of variable. The only reason your call to TryParse is invalid is because it is expecting an object of type int , not Nullable<int> .

If you are writing your own method, you can declare your argument types to be whatever you'd like, including int? . For example:

public void SomeMethod(string input, out int? output)