如何从C ++ dll导入结构？

Question

How can I create a struct in C++ put it in a dll and use from C# code? I'm developing an application using C# and C++ where each process talk to each one other using named-pipes and I'd like to share data between via structs (pass raw bytes to process and then cast it to struct type) but rather than define two structs one in C++ and another in C# with same memory alignment, members names and such (which is very error prone, if I update the C++ one and forget the C#'s one) I'd like to creare only one so that there's only one place to change. My idea is (if even possible, I think it isn't not possible due P/invoke limitations) define this struct in a dll written in C++ and just use it from my C# application. This is just my idea; any different approach to solve this is very welcome too.

Answer 1

You can't. Structs and classes are not part of the exposed ABI, the DLL doesn't define them in any way. That's part of the reason for DLL hell in the C/C++ world, your function definitions state the name of the struct they take, but the details of the implementation of that struct aren't actually exposed or defined anywhere in the DLL itself.

C and C++ rely on the use of header files to inform dependent projects of the layout of structs and classes, as that information isn't exposed via the DLL or lib file. Since it's not possible in native code, it's going to be doubly not possible (or, pedantically, just as impossible) in managed code.

Some alternatives I'd recommend looking into if über performance is not a constraint would be some sort of serialization library. You can get some crazy things done with something like Google's protobuf, eliminating p/invoke and compatibility concerns, etc. if you want to focus on rapid development and consistency. There are also ways to generate C# and C/C++ source code with the relevant structures via a script ranging from a hack-it-yourself C/Python/Perl script to generate a struct for C and C# to complete projects that focus on creating source code from language-agnostic struct definitions, but that's probably outside the scope of this answer.