Accessing C++ class enum values from C#

Question

I am trying to access an enum in a C++ class header (.h) from C#. Is there a simple way of doing this? Every example I have seen involves compiling the class into a .dll, which for this example is kind of a waste because the function of this class is pretty limited.

Edit by request: The C++ library CAN be modified. In fact, the C++ library is the major component of the project(firmware) and is developed by other members of my team, the C# (my part) is just for unit testing purposes.

Does it ever change? The easiest (if you don't need to interop b/w C# and C++) would be to just replicate the Enum in C#. — D Stanley
– D Stanley, Commented Jan 4, 2013 at 16:14
As stanley said, just create a similar enum in C#. Only drawback is that if someone changes the C++ enum, the corresponding changes has to be made in C# class. — Ganesh R.
– Ganesh R., Commented Jan 4, 2013 at 16:15
Have you considered writing a small script that parses the .h file and generates a .cs file with the enum? (e.g., using T4 Templating) — dtb
– dtb, Commented Jan 4, 2013 at 16:15
It is possible that it would change, which is why we want to make the C# code read from the C++ code, if you will. One of the developers changed the values in C++, but forgot to update the values in C#, and this is the reason the unit tests failed... — Kyle Preiksa
– Kyle Preiksa, Commented Jan 4, 2013 at 16:16
@dtb, I have not actually thought about that... it does seem like an easier solution than actually linking the code. — Kyle Preiksa
– Kyle Preiksa, Commented Jan 4, 2013 at 16:18

cdhowie · Accepted Answer · 2013-01-04 16:15:39Z

7

Realistically, you have three options:

Create a glue library that exports a C function (extern "C") that includes this header and returns the enum value you are interested in, then P/Invoke this library from C#.
Hard-code the value in your C# code.
Write a C++ parser and extract the value that way. (Either a complete C++ parser, which would be preferable, or you can be lazy and write a simple regex parser that will work on this particular version of the C++ header, but might break in the future if the code changes in a way you didn't expect.)

answered Jan 4, 2013 at 16:15

cdhowie

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3 Comments

Yakk - Adam Nevraumont Over a year ago

4. note that the enum Foo { base=1, next, nextnext, blah }; syntax is common between the two. Create a file that contains just the enum. #include it in a C++ header file where you need it. Now you don't have to fully parse C++, just manage to get a file containing an enum definition into your C# project.

Mooing Duck Over a year ago

@cdhowie, want to copy that comment into the answer?

cdhowie Over a year ago

The question does not specify whether the C++ header is part of the same codebase or not. Therefore I'm trying to keep my answer to just those techniques that work with an external C++ library -- that is, one that cannot be easily modified. The people who land here from a Google search are more likely to be in this situation with a third-party library. If the OP edits the question to note that the C++ library is part of the same codebase and therefore can be modified as part of the solution, then I would definitely be willing to incorporate that technique into my answer.

Timo Geusch · Accepted Answer · 2013-01-04 16:16:12Z

0

In order to access the C++ enum, you have to turn the C++ class into something that .NET can recognise, which either means compiling it as C++/CLI (if that is an option) or turning into a DLL that the .NET interop can access.

answered Jan 4, 2013 at 16:16

Timo Geusch

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Comments

D Stanley · Accepted Answer · 2013-01-04 19:57:49Z

0

Well, this freaks the CS pre-compiler out a bit, but it builds:

#if CSHARP

namespace Test
{
    public enum SharedEnum

#endif //CSHARP

#if CPP
    typedef enum SharedEnum 
#endif //CPP
    {
        One,
        Two,
        Three
    }
#if CPP
    SharedEnum 
#endif //CPP
    ;
#if CSHARP
};
#endif

Just add the Conditional Compilation symbol CSHARP to your C# project, add the existing .cs file and the preprocessor definition CPP to your C++ project.

(credit to Yakk for having the same idea)

edited Jan 4, 2013 at 19:57

answered Jan 4, 2013 at 17:03

D Stanley

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1 Comment

Mooing Duck Over a year ago

Can be simplified: C++, C#

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