Questions about IntPtr

When I make some P/Invoke or COM InterOP, I often bump into the IntPtr. So here is a couple of questions:

• Everyone said that IntPtr is a struct, so what's in it? I can only think of an 32bit/64bit integer which is the address it points to. Anything else?

• Where is the IntPtr located? If it is a struct, I believe it should be in the CLR managed stack. But what if I pass an IntPtr to an unmanaged method when doing p/invoke, isn't it passed to the unmanaged stack? Will it be copied to the unmanaged stack? There're managed and unmanaged heaps in a proce开发者_如何学Pythonss address space, does this seperation also exist for a process' stack?

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An IntPtr is simply an integer that is guaranteed to be the size of a pointer. Because of that, it is often used to contain pointers in contexts where it would be considered "unsafe" to have a pointer.

But, like a pointer, it's just a number. If it contains an address then the address could be valid or invalid in this process. It could be aligned or unaligned, it could be to a location on the current thread's stack or another thread's stack or the managed heap or some unmanaged heap. It's just a number; whether the interpretation of that number as a pointer is meaningful or safe is up to you to determine.

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• Yes, it's just a pointer. That's all.

• I think you've bought into the "structs are on the stack, classes are on the heap" myth. I strongly recommend that you read Eric Lippert's blog entry on this (and another one).

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Everyone said that IntPtr is a struct, so what's in it? I can only think of an 32bit/64bit integer which is the address it points to. Anything else?

Using Reflector, you can see that it contains only one instance field, of type void*

private unsafe void* m_value;

Where is the IntPtr located? If it is a struct, I believe it should be in the CLR managed stack. But what if I pass an IntPtr to an unmanaged method when doing p/invoke, isn't it passed to the unmanaged stack? Will it be copied to the unmanaged stack? There're managed and unmanaged heaps in a process address space, does this seperation also exist for a process' stack?

First, structs are not necessarily stored on the stack. This is a common misconception: they can be stored on the stack, but it doesn't mean it's always the case (see this article for details).

Also, there is no "process stack": each thread has its own stack.

I don't know all the details of how p/invoke works, but basically, yes, the IntPtr value is copied to unmanaged memory.

If you want more information about interop with unmanaged code, you might be interested in this article.