What does a double question mark do in C#?

2018-06-02 11:47:41

Possible Duplicates:
?? Null Coalescing Operator --> What does coalescing mean?
What do two question marks together mean in C#?

I couldn't find this question being asked here so I figured I would ask it. What does a double question mark do in C#?

Example:

x = y ?? z;

This is a null coalescing operator. The method above states x is assigned y's value, unless y is null, in which case it is assigned z's value.

如果不是null，则使用y，否则使用z

From Wikipedia:

It's the null-coalesce operator and shorthand for this:

x = (y != null ? y : z);

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