C# IntPtr.Zero 等价于 null 吗？
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Is IntPtr.Zero equivalent to null?
提问by SwDevMan81
I am trying to setup ReadFileto run asynchronously and according to MSDN, I need to set lpNumberOfBytesReadto null:
我正在尝试设置ReadFile为异步运行，根据MSDN，我需要设置lpNumberOfBytesRead为null：
"Use NULL for this parameter if this is an asynchronous operation to avoid potentially erroneous results."
“如果这是一个异步操作，请为此参数使用 NULL 以避免潜在的错误结果。”
For example, if I have the following:
例如，如果我有以下内容：
[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
public static extern bool ReadFile(
IntPtr hFile,
out byte[] aBuffer,
int cbToRead,
IntPtr cbThatWereRead,
ref OVERLAPPED pOverlapped
);
and I call it like this (with the intention of having the 4th parameter being null):
我这样称呼它（目的是让第 4 个参数为空）：
Win32API.ReadFile(readHandle, out data_read, Win32API.BUFFER_SIZE, IntPtr.Zero, ref over_lapped);
will that be the same as calling it with null? If not, what should I change in the declaration or in the function call itself?
这和用null调用它一样吗？如果不是，我应该在声明或函数调用本身中更改什么？
I was also curious if I should be using SafeHandleor HandleRefinstead of IntPtrfor the hFilereference? I know to make sure that I close the handle with CloseHandle(IntPtr)when I'm done with it, just not sure if there is any othe reason to use the other two options over IntPtr. I am also tryingn to avoid using unsafe code.
我也好奇，如果我应该使用SafeHandle或HandleRef代替IntPtr的hFile参考？我知道要确保CloseHandle(IntPtr)在完成后关闭手柄，只是不确定是否有任何其他理由在IntPtr. 我也试图避免使用不安全的代码。
EDIT: As it turns out, I shouldnt be setting the fourth parameter to IntPtr.Zeroanyway, because even though I am running asynchronously, it could still return right away. See Asynchronous Disk I/O. Ahh, I love contradicting stories.
编辑：事实证明，IntPtr.Zero无论如何我都不应该将第四个参数设置为，因为即使我异步运行，它仍然可以立即返回。请参阅异步磁盘 I/O。啊，我喜欢矛盾的故事。
采纳答案by Michael
For P/Invoke purposes like you've listed, you should use IntPtr.Zeroin place of NULL. Note that this is not equivalent to the C# nullkeyword, however.
对于P / Invoke的目的，就像你上市，你应该使用IntPtr.Zero的地方NULL。但是请注意，这并不等同于 C#null关键字。
回答by Yannick Motton
You cannot assign null to a value-type. A reference-type can be null, as in, not referring to an object instance, but a value-type always has a value.
您不能将 null 分配给值类型。引用类型可以为空，例如，不引用对象实例，但值类型始终具有值。
IntPtr.Zero is just a constant value that represents a null pointer.
IntPtr.Zero 只是一个表示空指针的常量值。
回答by xanatos
Be aware that there is a bug (feature??) in C# >= 2.0, where
请注意，在 C# >= 2.0 中存在一个错误（功能？？），其中
if (IntPtr.Zero == null)
{
// Won't enter here
}
will compile correctly, but it won't ever enter in the if.
将正确编译，但它永远不会进入if.
I opened an issue on the github of roslynand they replied that they won't fix it because there are projects that are built with warnings-as-errors. Still there is a partial fix for this: there is a strictcompilation mode that generates this warning:
我在roslyn的github上打开了一个问题，他们回答说他们不会修复它，因为有些项目是用警告作为错误构建的。仍然有一个部分修复：有一个strict编译模式会产生这个警告：
<Features>strict</Features>
