Unmanaged C++ libraries - differences between VS2005 and VS2008?

Question

Hi, I'll preface this by saying I'm a C# programmer who inherited horrible code with no documentation. I have an unmanaged C++ library wrapped with managed code that worked fine in VS2003 with .Net 1.1 Framework. I'm trying to get it upgraded to at least .Net 2.0.

I have the unmanaged C++ library that was compiled with "MSVC 8.x" (thus equivalent to VS 2005, I assume). I've been trying to migrate everything to VS2008 and still have some issues with this library at runtime.

My question is this: should this library work with VS2008? Or should I be developing in VS2005 if the library was compiled with VC8.x?

Any thoughts would be greatly appreciated. Thanks!

Answer 1

It should work, I expect that you are having issues with your marshalling. It is probably stuff that was declared incorrectly for PInvoking that managed to work in .NET 1.1 but not in later versions.

You don't say what sort of problems you are having at run time, nor do you state how you access your library. For example, do you compile your library along with your project? If so, can you turn on unmanaged debugging in your C# project and step into the code you are having trouble with? How are you calling the unmanaged code? Is it through PInvoke, or do you have managed C++ wrappers?

In my experience, the best solution for calling out to a legacy unmanaged library is to add a managed wrapper library for your legacy library written in managed C++. This way you present a managed interface for your library for all .NET languages to consume and you don't have to worry about getting your PInvoke signatures correct.

Your project should look something like this.

C# Application -> Manage C++ Wrapper DLL -> Legacy DLL

Answer 2

It can depend what else the lib relies on. For example, if you are using the STL across the library interfaces then it would be a bad idea to have the library compiled with a different version to the client. However, if the library presents a simple C style function interface then you shouldn't have problems.

If you have the source code for the library then I would recommend trying to port it to VS2008. In general it is much less hassle in the long run to have everything in the same development environment.

How are you wrapping the unmanaged lib ... presumably using managed extensions for C++ if it dates back to VS2003. This is now deprecated and has been replaced with C++/CLI as of VS2005. Whilst the newer compilers support a /clr:oldSyntax switch to still compile the old code there are definitely issues with it. We have old code that will not compile on VS2005(8) using this switch.

Answer 3

--Rob Prouse:
The wrapper uses managed C++, no PInvoke. The wrapper is compiled into a DLL that is then used by another application (as you illustrated).

The legacy code produces graphics objects. When I try to get the handle to an image, I get a null exception instead. The debugger doesn't let me get farther into the code to figure out why. Everything else seems to run ok - the other data objects needed to create the image exist and appear to be correct. (Sorry, I know that is still a pretty vague description.)

--Rob Walker:
I unfortunately do not have the source code. Not sure about "using the STL across the library interfaces". Does graphics fall under that category?

I was able to get my application to run with using the /clr:oldSyntax switch, but that's where I get the null handles to images. I tried to put in all the modifications so that it would compile with /clr, but then I kept getting link errors that I couldn't resolve. (The linker kept complaining about not being able to find files even though those files were in the folder where it was looking.)

Answer 4

Well I am very new to Visual C++ and for that i have just installed VS2008 pro. My prob is that my mentor has given me a VS2005 built project and since I have installed 2008 i do not want to switchback to 2005

But Each time I compile this project(after automatic up-gradation by VS2008) I am getting the following kind of error

FrameGrabber.h(41) : fatal error C1083: Cannot open include file: 'streams.h': No such file or directory

kindly help me out.

BTW this project works fine via VS2005.