Calling Unmanaged code from Managed code

think1stsolutions · May 30th, 2011, 04:34 PM

I have an unmanaged C++ DLL, I have the source to. I am trying to extend its functionality. I have successfully called existing methods in the DLL in a brute force way. I simply added the DLL as a project reference to my managed C# project and did a new on the desired class and called the methods.

As I have been studying up on this topic, I ran across the System.RunTime.Interop.Marshal set of static methods. Also, PInvoke. It is not clear to me when I should use one approach over another. I was wondering if someone here could tell me more about them. I am interested in knowing when should you use any of these approaches? when should you not?

My application is a managed wrapper around the unmanaged c++ DLL. The unmanaged DLL is not using COM or ATL. It is just plain C++. I am passing binary data. This data is transformed into another binary data using a complex algorithm and returned. Speed & multithreading is important, since it will be called by several threads.

Mike

ChristianNagel · May 31st, 2011, 02:23 AM

Hi Mike,

As you've added the DLL as a project reference, created an instance and called the methods - are your sure not having a COM library?
Platform Invoke is used on unmanaged DLLs that export functions (see dumpbin /exports lib.dll).
The Marshal class has several helper methods for managed/unmanaged interop, both for DllImport and COM interop scenarios.

Hope this helps.

think1stsolutions · May 31st, 2011, 08:45 AM

I'm not exactly sure how to tell if it uses COM or not. I know I didn't register the DLL or anything like that.

Within my managed C# project
1. I made a Project Reference to the unmanaged C++ project
2. Added a Using statement to that DLL
3. Then created an instance of the class
4. Accessed a method on the class

That is all I did. I did not use PInvoke, DllImport or anything like that.

ChristianNagel · May 31st, 2011, 09:30 AM

There's also a way to use COM without registration. However, you referenced the unmanaged C++ project from the C# project? So you have the C++ project opened within the same solution? If you build the C++ project with Visual Studio, it might also do the registration of the COM server.
Can you do a "tblimp comserver.dll"? In that case a type library is included with the unmanaged C++ DLL and it's definitely a COM server. The type library could also be in a different file from the DLL.

think1stsolutions · May 31st, 2011, 09:44 AM

When I run tlbimp on my dll it returns
error Tl1002: The input file "my.dll" is not a valid type library.

ChristianNagel · May 31st, 2011, 10:03 AM

ok, the type library might still be outside of the DLL.
How does your C++ class look like?
Maybe

Code:

public ref class ClassName
{
};

In that case it's a managed version of C++: C++/CLR
Can you do ildasm on the my.dll?

think1stsolutions · May 31st, 2011, 09:34 PM

ILDASM produces output that looks like a class view of my DLL.

The class that I access is declared just like your example:

Code:

public ref class Foo
{
};

So does that mean it is using COM or managed C++? I assumed it is not managed C++ because I cannot make references to managed objects.

ChristianNagel · June 1st, 2011, 01:43 AM

You can use this C++ class like a .NET class because it is a .NET class. You're not using COM.
The ref keyword declares a managed reference type with C++/CLR. With the C++ compiler settings you will see the /clr option enabled. public ref class Foo is a managed reference type (class in C#), public value class Foo is a managed value type (struct in C#).
How do you see that you cannot make references to managed objects with the C++ project? It should be possible to reference .NET assemblies with the C++ project and use the public types there without problems. Just the syntax to use these types is a little different to normal C++.
With the Pro C# book you can find mapping between C++/CLR and C# with one of the downloadable chapters.