C＃的P / Invoke：一个包含函数指针编组结构

对不起，后面的详细介绍。我需要的洞察力从别人知道比我更好的P / Invoke的内部结构。

Sorry for the verbose introduction that follows. I need insight from someone knowing P/Invoke internals better than I do.

下面是我如何编组包含函数指针从C到C＃结构。我想知道它是否是做它的清洁和/或最有效的方式。

Here is how I'm marshalling structures containing function pointers from C to C#. I would like to know whether it's the cleanest and/or most efficient way of doing it.

我在一机DLL在C语言编写的，它提供了以下条目接口点：

I'm interfacing with a native DLL coded in C that provides the following entry point:

void* getInterface(int id);

您必须通过 getInterface（INT）以下枚举值之一：

You have to pass getInterface(int) one of the following enum values:

enum INTERFACES
{
  FOO,
  BAR
};

返回一个指向包含类的函数指针的结构：

Which returns a pointer to a structure containing function pointers like:

typedef struct IFOO
{
  void (*method1)(void* self, int a, float b);
  void (*method2)(void* self, int a, float b, int c);
} IFoo;

和这里是你如何用C使用它：

And here is how you use it in C:

IFoo* interface = (IFoo*)getInterface(FOO);
interface->method1(obj, 0, 1.0f); // where obj is an instance of an object
                                  // implementing the IFoo interface.

在C＃我有一个图书馆类映射 getInterface（INT）使用入口点的p / Invoke。

In C# I have a Library class that maps the getInterface(int) entry point using P/Invoke.

class Library
{
  [DllImport("MyDLL"), EntryPoint="getInterface", CallingConvention=CallingConvention.Cdecl)]
  public static extern IntPtr GetInterface(int id);
};

然后我定义的：

Then I defined:

struct IFoo
{
  public M1 method1;
  public M2 method2;


  [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
  public delegate void M1(IntPtr self, int a, float b);

  [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
  public delegate void M2(IntPtr self, int a, float b, int c);
}

和我使用这种方式：

IntPtr address = Library.GetInterface((int)Interfaces.FOO);
IFoo i = (IFoo)Marshal.PtrToStructure(address, typeof(IFoo));

i.method1(obj, 0, 1.0f): // where obj is an instance of an object
                         // implementing the IFoo interface.

我有以下问题：

I have the following questions:

1. 是映射整个结构比使用 Marshal.GetDelegateForFunctionPointer（）映射结构内部的单指针？

由于我大多不需要通过一个接口暴露的所有方法，我可以做（测试和工程）：

Since I mostly don't need all the methods exposed by an interface, I can do (tested and works):

unsafe
{
  IntPtr address = Library.GetInterface(id);
  IntPtr m2address = new IntPtr(((void**)address.toPointer())[1]);


  M2 method2 = (M2)Marshal.GetDelegateForFunctionPointer(m2address, typeof(M2));


  method2(obj, 0, 1.0f, 1);
}