C# p/invoke C 函数返回指向结构的指针
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p/invoke C function that returns pointer to a struct
提问by THX-1138
How do I declare in C# a C function that returns a pointer to a structure?
如何在 C# 中声明一个返回指向结构的指针的 C 函数？
I believe following is one way to do that, followed by Marshal.PtrToStructureto get actual structure value.
我相信以下是一种方法，其次是Marshal.PtrToStructure以获得实际的结构值。
// C-function
SimpleStruct * Function(void);
// C# import
[DllImport("MyDll.dll")]
public static extern IntPtr Function();
- Am I correct about that?
- Are there other ways to accomplish the same? (It would be OK to get struct back by value)
- 我是否正确？
- 还有其他方法可以实现相同的目标吗？（按值取回 struct 就可以了）
采纳答案by Shea
Since the function returns a pointer (hopefully not a locally allocated one?) your best bet is to manually marshal it (via Marshal.PtrToStructure).
由于该函数返回一个指针（希望不是本地分配的指针？），您最好的办法是手动对其进行编组（通过Marshal.PtrToStructure）。
If it were a parameter you could create a managed version of the structure using the PInvoke Interop Assistant then pass it via ref or out.
如果它是一个参数，您可以使用 PInvoke Interop Assistant 创建结构的托管版本，然后通过 ref 或 out 传递它。
回答by Darren Kopp
I am not an expert here at all, but I happened to be looking at a piece of code (that i don't understand completely mind you) that is doing this same thing.
我根本不是这里的专家，但我碰巧正在看一段代码（我不完全理解）正在做同样的事情。
Here is what they are doing
这是他们在做什么
[DllImport("")]
private static extern short MethodName([In,Out] ref StructureName variable);
and then on the structure they have the following attribute
然后在结构上，它们具有以下属性
[StructLayout(LayoutKind.Sequential, Size = #)]
public struct StructureName {}
I think the part you are looking for is the [In,Out] part, and since it's being passed via ref, you should be getting the same data back.
我认为您正在寻找的部分是 [In,Out] 部分，因为它是通过 ref 传递的，所以您应该得到相同的数据。
marked as community wiki so people can fix this if wrong.
标记为社区维基，以便人们可以在错误时解决此问题。
回答by Eric Burnett
Caveat: this will only work if the pointer returned is to memory already managed by the CLR
警告：这仅在返回的指针指向已由 CLR 管理的内存时才有效
I believe what you are looking for is
我相信你正在寻找的是
// C# import
[DllImport("MyDll.dll")]
[return : MarshalAs(UnmanagedType.LPStruct)]
public static extern StructureName Function();
[StructLayout(LayoutKind.Sequential)]
public class StructureName {}
This should eliminate the need for any manual Marshal.PtrToStructurecalls. Depending on what your structure contains, you may need to tag some fields with MarshalAsattributes as appropriate. MSDNhas a good example of this.
这应该消除对任何手动Marshal.PtrToStructure调用的需要。根据您的结构所包含的内容，您可能需要MarshalAs适当地使用属性标记某些字段。MSDN有一个很好的例子。
