What does a double question mark do in C#? [duplicate]

This question already has answers here: Closed 13 years ago.

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开发者_JAVA技巧 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.

---

From Wikipedia:

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

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

---

Use y if not null, otherwise use z.

---

If a the value y is null then the value z is assigned.

For example:

x = Person.Name ?? "No Name";

If name is null x will have the value "No Name"

---

If y is null x will be set to z.

---

.Net framework 2.0 onwards allow null values to Nullable value types.

here in this case, it says x equals y if it has some value (ie not null) or else equals z

---

As others have stated, it is the null coalescing operator.

MSDN information on this:

https://learn.microsoft.com/dotnet/csharp/language-reference/operators/null-coalescing-operator