Class in a DLL

[HarryW]

Put the definition of the class in a header file and include it in whatever you want to share the class with. If you want an instance of the class (an object), you can put that in a DLL and share it.

[CornedBee]

Yes, with vc++ you best create a sample win32 dll that exports a few symbols and see how it's done.
With others I don't know how, but it's surely possible.

All the buzzt
CornedBee

[Wynd]

Vlatko: You mean just include it like any normal file and compile it into the program?

[HarryW]

Umm do you mean me?

Anyway, yeah just include the header file in whatever C++ project with which you want to access the DLL containing the shared object.

[Wynd]

Yeah, sorry, for some reason I thought you were him.

Anyway, I don't know what you mean. I know how to include the file, link it, etc., but how would you set it up to export the class?

[HarryW]

What do you mean 'export the class' ? You can put an instance of a class in a DLL and share it with your exe code. You don't get the class definition from the DLL.

I think if you made the class COM-compatible you could probably register it with Windows and let Windows deal with it.

[parksie]

class __declspec(dllexport) MyClass {
    // Contents here
};

Use dllimport for the import header file, and dllexport when creating the DLL. You'd need to link with the created .lib file when you make the DLL.

Oh, and I think you need to use the same version of VC++ for the DLL and the using program.

[HarryW]

What would you put in the header file if you're exporting the class definition from the DLL?

[parksie]

__declspec(dllexport) as I said earlier

[Wynd]

Ok, the DLL compiles fine, but I get a link error when I try to write a simple program using the class. I attached my source so you can see where it went wrong.

error LNK2001: unresolved external symbol "__declspec(dllimport) class MyClass inst" (__imp_?inst@@3VMyClass@@A)

[parksie]

You need two copies of the header. One to create the DLL, and one to use it. I use a preprocessor directive to decide what to use, that way I can get by with the same header. A specific symbol is defined in project settings for the DLL project.

[Wynd]

What preprocessor directve would that be?

[parksie]

Well, something like this:

#ifdef _IKDLL_INT
#define IKDLL __declspec(dllexport)
#else
#define IKDLL __declspec(dllimport)
#endif

class IKDLL MyClass {
// blah
};

Then in project settings add _IKDLL_INT to the list of predefined symbols. Pretty simple really

[Wynd]

error C2071: 'inst' : illegal storage class

[CornedBee]

note that i set the library to single threaded, because I forgot to install the multithread CRT dlls


All the buzzt
CornedBee

[CornedBee]

forgot again

[HarryW]

Ah right that code was meant for the headers not the DLL.....

Hang on a minute... that's what I was suggesting in the first place, minus the __declspec bit. What's that for that just including the class definition wouldn't do?

[CornedBee]

It tells the linker not to search for the class in a normal library or module, but rather the import library. (I think)
Also, I'm not sure if I posted the right files before. Tell me if not.

[HarryW]

Don't you still give the class definition in the header though? Or do you only define the interface and leave the implementation in the library?

[CornedBee]

The implementation is in the library.

[HarryW]

Gotcha. Thanks