是什么?类型声明后的 C# 中的运算符是什么意思? [英] What does the ? operator mean in C# after a type declaration?

问题描述

我有一些带有以下数组声明的 C# 代码.注意 Color 之后的单个 ?.

I have some C# code with the following array declaration. Note the single ? after Color.

private Color?[,] scratch;

在我的调查中，我发现如果你有这样的代码:

In my investigating I have found that if you you have code such as:

int? a;

变量 a 未初始化.您将在何时何地使用它?

The variable a is not initialized. When and where would you use this?

推荐答案

? 只是语法糖，表示该字段为 Nullable.它实际上是 Nullable.

? is just syntactic sugar, it means that the field is Nullable. It is actually short for Nullable<T>.

在 C# 和 Visual Basic 中，您可以使用?值类型后的符号.例如，整数?在 C# 或整数?在 Visual Basic 中声明了一个可以赋值的整数值类型空.

In C# and Visual Basic, you mark a value type as nullable by using the ? notation after the value type. For example, int? in C# or Integer? in Visual Basic declares an integer value type that can be assigned null.

您不能将 null 分配给值类型，int 作为值类型不能保存 null 值，int? 另一方面可以存储空值.

You can't assign null to value types, int being a value type can't hold null value, int? on the other hand can store null value.

Color 的情况也是如此，因为它是一个结构 (因此是值类型)，并且它不能保存空值，Color?[,] 您正在制作一个可为空颜色的数组.

Same is the case with Color, since it is a structure (thus value type) and it can't hold null values, with Color?[,] you are making an array of nullable Color.

对于您的问题:

变量a"未初始化.您将在何时何地使用这个?

The variable 'a' is not initialized. When and where would you use this?

通过将 ? 与变量一起使用并不会使其使用 null 或任何其他值进行初始化，它仍然需要进行初始化.

By using ? with variable doesn't make it initialized with null or any other value, it is still has to be initialized.

int? a = null; 

int b = null;//error since b is not nullable

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