Calling C++ unmanaged member functions from C# when member functions were not exported?

Question

5.00/5 (1 vote)

See more:

I have an unmanaged DLL that exports only a C style factory method that returns a new instance of a class (simplified here to look simple).

hello.h

C++

#if defined(HWLIBRARY_EXPORT) // inside DLL
#   define HWAPI   __declspec(dllexport)
#else // outside DLL
#   define HWAPI   __declspec(dllimport)
#endif

struct HelloWorld{
   public:
    virtual void sayHello() = 0;
    virtual void release() = 0;
};
extern "C" HWAPI HelloWorld* GetHW();

hello.cpp

C++

 #include "hello.h"

struct HelloWorldImpl : HelloWorld
{
    void sayHello(){
        int triv;
        std::cout<<"Hello World!";
        std::cin>>triv;
    };
    void release(){
        this->HelloWorldImpl::~HelloWorldImpl();
    };
};
HelloWorld* GetHW(){
    HelloWorld* ptr = new HelloWorldImpl();
    return ptr;
};

Now, I can use dllimport to access GetHW() but is there a way to access the member functions of the returned 'struct'... ie, sayHello and release?

This question was asked a while before. I was also stuck with the same problem.

When i googled, able to find out two solutions.

Solution1: Expose all the member functions in the C-style for the existing dll. Which i cant do, as it is a 3rd party dll.

Solution2: Write a managed C++ dll exposing the functionality of native C++ dll, which later can be used in your C# dll. Here many classes/functions are present. So, creating would take most of the time.

i got the above solutions from the link below.
How to Marshal a C++ Class[^]

Please let me know if there is any better solution other than the above two solutions?

Posted 20-Apr-15 4:19am

eswarpabolu

Updated 20-Apr-15 4:21am

v2

Add a Solution

Comments

Sergey Alexandrovich Kryukov 20-Apr-15 11:14am

Interesting question, my 5.
I have a good question for you: do you have this C++ source code and the possibility to update it? If you can, there is a really elegant and really reliable, non-intrusive solution.
—SA

eswarpabolu 21-Apr-15 1:28am

i have the source code for C++ solution. But what i though was not to touch C++ source. If there is any possibility to do it in C#, it would be great.

If there is no alternative, i need to follow any one of the specified two solutions.

If u can propose some other alternative, please give u r inputs.

Sergey Alexandrovich Kryukov 21-Apr-15 9:22am

Sure. Please see Solution 1.
—SA

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Accepted Answer · 2015-04-21T03:21:00

eswarpabolu wrote:
I have the source code for C++ solution. But what iI though was not to touch C++ source. If there is any possibility to do it in C#, it would be great.

I still suggest you to modify C++ source, because it would give you a serious benefit. But you don't need to modify any code. You could do a lot better: only add some new file(s) to the code in most unobtrusive way, so your present functionality would not be compromised.

The idea is: you can use C++/CLI (not just native C++) and essentially use "CLI" part of it to expose some code as managed. You can make you C++ project mixed-mode (managed+unmanaged) C++/CLI module and .NET assembly at the same time, with possibility of dual use: .NET assemblies can reference your C++/CLI assembly as any other assembly, and unmanaged native units can just keep using its executable module (DLL, in this case) as any other native DLL.

As you can freely mix managed and unmanaged code in C++/CLI, you could wrap you native class(es) into managed "ref" CLI types and exposed those you need to expose to other assemblies using public access modifier. It's better not to change any existing files, just add some separate ones.

This way, despite of some code overhead, seems to most beneficial, because it is the most reliable and maintainable: you won't be dependent on the subtleties of marshaling and internal representation of types; moreover, modification of the types to be exposed can be painless.

Please see: https://msdn.microsoft.com/en-us/library/ms235282.aspx[^].

See also:
http://en.wikipedia.org/wiki/C%2B%2B/CLI[^],
http://www.ecma-international.org/publications/standards/Ecma-372.htm[^],
http://www.gotw.ca/publications/C++CLIRationale.pdf[^],
http://blogs.msdn.com/hsutter/archive/2003/11/23/53519.aspx[^].

And see also my past answers:
How to invoke C++ DLL in ASP.NET?[^],
How do I catch native c++ exception in managed c++ class?[^],
Dealing with windows form application[^].

—SA