Writing the C wrapper for C++ dlls

Hi all,

After doing some research, it seems the only way to use unmanaged c++ code in c# is to write a c-wrapper. I've googled for any decent examples/tutorials on exactly how to do this, but all i come up with is some rhetoric on the subject, and no examples :(

Would any of you kind souls out there mind giving me an example of how to do this? Something as simple as one little function would suffice. I know it's a lot to ask, but i really would like to know how to do this, since I'm writing a .NET application that will need to preform some pretty intense calculations. Anything you could impart on me would be a huge and much appreciated help.

Thank you in advance.

http://msdn.microsoft.com/en-us/magazine/cc301501.aspx