Calling C# from C++, Reverse P/Invoke, Mixed Mode

问题:

As I understand it I can use reverse P/Invoke to call C# from C++. Reverse P/Invoke is simply a case of:

1. Create you managed (c#) class.
2. Create a c++/cli (formerly managed c++) class library project. Use this to call the managed c# class (presumably via a reference).
3. Call the c++/cli code from native c++.

Questions:

1. Is this correct?
2. Is the DLL created at step 2 known as a mixed mode DLL?
3. Has C++/CLI completely superseded Managed C++ as far as MS are concerned?
4. Is COM completely avoided using this approach?
5. At what point would the CLR be created and run, and by whom?

Thanks in advance

回答1:

Here are the answers to the best of my knowledge:

1. Yes
2. Yes, it is a mixed mode DLL (In fact, you can make one file of your native C++ project managed and create this C++/CLI class in that file and call the code directly from that file. You don't even need a separate DLL to accomplish this.
3. C++/CLI and Managed C++ both represent same thing. The only difference is that in the older version till Visual Studio 2003, it was termed as Managed C++. Later on, the syntax was changed quite a lot and it was renamed as C++/CLI. Have a look at this link for details.
4. Yes
5. CLR will be used whenever a call to the managed DLL is made.

回答2:

Note, you can also do a IL roundtrip of the C# dll and export static methods, which work basically the same as the exports in C++/CLI. However, this is always a post-compile step, and it does have some caveats (which your C++/CLI export have too, btw.).

You can ILDASM both the C# and the C++/CLI DLLs to see how exports are don; it is something like this (from a sample on the net):

// unmexports.il
// Compile with : ilasm unmexports.il /dll
assembly extern mscorlib {}
..assembly UnmExports {}
..module UnmExports.dll
// This flag is important
..corflags 0x00000002
// This instructs the CLR to create a marshaling thunk for the unmanaged caller
..vtfixup [1] int32 fromunmanaged at VT_01
..data VT_01 = int32(0)
..method public static void foo()
{
..vtentry 1:1
..export [1] as foo
ldstr "Hello from managed world"
call void [mscorlib]System.Console::WriteLine(string)
ret
}

回答3:

With ilasm 2.0 you need less code because it can generate most of the gunk by itself. Only the .export directive is really needed now.

// unmexports.il
// Compile with : ilasm unmexports.il /dll
.assembly extern mscorlib { auto }
.assembly UnmExports {}
.module UnmExports.dll
.method public static void foo()
{
  .export [1] as foo
  ldstr "Hello from managed world"
  call void [mscorlib]System.Console::WriteLine(string)
  ret
}