void 子程序返回什么? [英] What does a void subroutine return?

问题描述

我刚刚对复数视力进行了评估，并得到了以下问题.

I was just doing an assessment on pluralsight and was given the following question.

void 子程序返回什么?"

"What does a void subroutine return?"

我的印象是 void 子程序没有返回任何内容，但这不是所提供的答案之一(多选题).

I was under the impression that a void subroutine did not return anything, but this was not one of the answers provided (Multiple choice question).

.Net 是否在后台返回值类型或者这个问题不正确?

Does .Net return a value type in the background or is this question incorrect?

我得到的选择是:整数布尔值细绳日期时间

The choices I was given were: Integer Boolean String Datetime

推荐答案

System.Void 不是 nothing ，它是一个 struct 因此是一个值类型.

System.Void is not nothing , it's a struct hence a value type.

但是，作为 Sub(VB.NET) 或返回"void(C#) 的方法并没有真正返回值.所以你不能写这样的东西:

However, a method that is a Sub(VB.NET) or "returns" void(C#) does not really return a value. So you cannot write something like this:

System.Void nothing = Foo(); // Foo is a void-method 

这不会编译(System.Void 不能在 C# 中使用 -- 使用 typeof(void) 来获取 void 类型对象").相关:为什么不是 System.Void?

This doesn't compile ("System.Void cannot be used from C# -- use typeof(void) to get the void type object"). Related: Why not System.Void?

正如 Jeroen 和其他人提到的，实际上 void 方法确实不返回任何内容，因此正确答案是:它什么都不返回".

As Jeroen and others have mentioned, actually a void method does really not return anything, so the correct answer was: "It returns nothing".

MSDN 提到它只在反射中有用:

MSDN mentioned that it's only useful in reflection:

"在 System.Reflection 命名空间中使用了 Void 结构，但是在典型应用中很少有用.Void 结构没有除了所有类型都继承自 Object 类的成员之外的成员."

"The Void structure is used in the System.Reflection namespace, but is rarely useful in a typical application. The Void structure has no members other than the ones all types inherit from the Object class."

如果您查看 void 关键字上的工具提示，您会看到它映射到 System.Void.但同样，这并不意味着它是从方法返回的.它只是一个不存在的返回值的占位符.我猜 void 由于历史原因也存在，因为 C# 是基于 C 的.

If you look at the tooltip on the void-keyword you see that it maps to System.Void. But again, that doesn't mean that it is returned from the method. It's just a placeholder for a non-existing return value. I guess that void also exists due to historical reasons since C# is based on C.

也值得一读:为什么 C 中的 void 意味着不无效?

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