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

Question

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++/

Answer 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.

Answer 2

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
}

Answer 3

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
}