Import a C++ .lib and .h file into a C# project?

问题:

I have just started a C# project and want to import a C++ .lib and it's corresponding header (.h) file.

I've read various posts that all mention .dll, rather than .lib, which is confusing me.

The image below shows the .lib and .h file I'm referring to, all I've done is drag them into the project.

Can anyone point me to a clearer explanation of how to go about doing this? I'm sure it can't be as hard as it seems.

回答1:

What you could do, is creating a C++/CLI wrapper and expose the functionality of the lib you want to use via your wrapper. The created wrapper dll you can easily reference in your C# project. This of course takes a little bit of work to create the managed/unmanaged wrapper, but will pay off in the long run.

To create a managed C++ project select under the C++ project templates CLR and Class Library. Here you can link to your lib, use the header file the way you are used to.

Next create a new class (ref class) and wrap your library in it. An example might look something like this:

LibHeader.h

int foo(...);

You write a wrapper class like this: Header:

Wrapper.h

public ref class MyWrapper
{
    public:
        int fooWrapped();
};

Your Implementation:

Wrapper.cpp

#include Libheader.h

int MyWrapper::fooWrapped()
{
     return foo();
}

Namespaces and all the good stuff omitted for simplicity. Now you can use MyWrapper in your C# code just as easy as any other managed class. Of course when the interface of the lib gets more complicated you have to think about it a bit more, but it might help to separate the lib-code from your application. Hope to have shed some light on it.

回答2:

This is, unfortunately, a non-trivial problem.

The reason is primarily due to the fact that C++ is an unmanaged language. C# is a managed language. Managed and unmanaged refers to how a language manages memory.

• C++ you must do your own memory management (allocating and freeing),
• C# .NET Framework does memory management with a garbage collector.

In your library code

You must make sure all of the places you call new, must call delete, and the same goes for malloc and free if you are using the C conventions.

You will have to create a bunch of wrapper classes around your function calls, and make sure you aren't leaking any memory in your C++ code.

The problem

Your main problem (to my knowledge) is you won't be able to call those functions straight in C# because you can't statically link unmanaged code into managed code.

You will have to write a .dll to wrap all your library functions in C++. Once you do, you can use the C# interop functionality to call those functions from the dll.

[DllImport("your_functions.dll", CharSet = CharSet.Auto)]
public extern void your_function();

回答3:

It is 'as hard as it seems'. C++ and C# are ambivalent. The first has deterministic destruction, the second not. Now, you write C++/cli delaying the destruction to some finalizer called by the garbage collector working in it's own thread, introducing problems all over the place (thread safety, are C++ members (used in c++/cli) valid?, ...). Even worse the GC might suggest C++ objects being tiny (a pointer) and provoke a kind of memory leak (due to late deallocating tiny objects). Essentially you end up in writing a GC on top of the C++/cli GC to delete non C++/cli (!) objects in the main thread or another. All that is insane, ...