双重问号在 C # 中有什么作用？

可能的复制品:
? ? Null 聚合算子—— > 聚合是什么意思？
两个问号一起在 C # 中意味着什么

我在这里找不到这个问题，所以我想我会问它。双重问号在 C # 中有什么作用？

例如:

x = y ?? z;

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If y is null x will be set to z.

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Use y if not null, otherwise use z.

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最佳答案

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.

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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"

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

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

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

MSDN information on this:

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.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