talking to C from C#

Question

I have a legacy code implemented in C (not C++). I would like to be able to call a few methods in this C code from my C# code (on Windows). What would be the best approach to interface between the two language? Please note that the method in C is not stateless. We need to call two methods:

1. initialization() => this will initialize the data structure and load data from files into memory. This method will be called once.
2. ComputeSomething(parameters) => there will be several calls from C# to this method.

Note: These two methods actually call several other methods but these are only the two methods that we would like to expose to C# (the code is quite complicated, that's why we do not want to port to C#)

I have been able to import the c code into visual studio and able to compile the code successfully. I know that we can probably implement the C code as windows service but I am looking for a solution that allow us to call C method from C# directly. Any pointers is highly appreciated! (is COM interop related to what I am looking to do?)

Answer 1

Hi there.

Sounds like you can use P/Invoke for this. Check out this site for tips:

http://www.pinvoke.net/

Also, try searching SO for advice on P/Invoke and Google for

c# pinvoke calling c code

I don't have any technical examples at hand, but I have written some .NET code which called Win32 API's via P/Invoke. The tricky part is getting the method signatures correct when passing parameters. This might help you out there.

Cheers. Jas.

Answer 2

Recent version of Visual Studio allow you to write C++ code that can call unsafe functions but still interface with CLR managed code. They call this "Implicit PInvoke," or "C++/CLR." Check out the MSDN article "Using C++ Interop" to learn more.

Managed code can't call unmanaged directly, so you need wrapper functions to handle the memory management issues and to translate between .NET objects and the data structures of your application. From the link above, check out the section on "How to: Wrap Native Class for Use by C#."