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.NET Forum / Languages / Managed C++ / June 2007Refering to Class, Types, and Functions from Dlls
Hi all, I have a DLL that I need to access. I've managed to load it and unload it successfully. The compiler is happy no complaints or warning. I need to refer to a class object that was defined in the class, and I'm not sure how to go about it. I understand that if I need to call a function I'd need to call GetProcAddress(hDll,"funcFoo"); that would return a pointer to the function and then I'd use the pointer to address the function inside of my program. what would I need to do to refer to the Dll, types. If I was in a regular C++ program, I would be doing something like ClassFoo.Host myhost; // assuming Host if an internal class, is public and is well defined. How would I be able to do that if my class Foo is defined inside the dll? -- Samir If it's a native app (not managed) then you simply include the header file of the type you want to reference.  SignatureBrowse http://connect.microsoft.com/VisualStudio/feedback/ and vote. http://www.peterRitchie.com/blog/ Microsoft MVP, Visual Developer - Visual C# > Hi all, > [quoted text clipped - 22 lines] > -- > Samir > If it's a native app (not managed) then you simply include the header file > of > the type you want to reference. Trying to dllimport native C++ classes is a bad idea which will cause you no end of trouble down the road. I suggest you rearchitect your application with a C-compatible interface (with proper memory manager separation), which is a proven and reliable means of developing DLLs. The object-oriented version would be COM, and I suggest that if someone gave you a closed source DLL that "contains a class", it is most likely a COM coclass. To confirm that, use the oleview SDK tool to check for the presence of a type library. To use it you load the DLL, GetProcAddress its DllRegisterServer function and call it, making Windows aware of the coclass, and then use CoCreateInstance to create an instance of the class, probably using the com_ptr compiler support. >> Hi all, >> [quoted text clipped - 22 lines] >> -- >> Samir > Trying to dllimport native C++ classes is a bad idea which will cause > you no end of trouble down the road. What problems are those? The only problems I have found have occured when I have had a mismatch between run-time library settings between providers and consumers of classes (i.e trying to free memory allocated by a different runtime library). Other than that it has been plain sailing. Obviously the components you write should be all written using the same version of the compiler, and so if that is not possible then its a bad idea. Peter >> Trying to dllimport native C++ classes is a bad idea which will cause >> you no end of trouble down the road. [quoted text clipped - 7 lines] > version of the compiler, and so if that is not possible then its a bad > idea. If you require all the components to be compiled with the same compiler, same macros, same settings, what do you gain by having a DLL? > Peter >> Obviously the components you write should be all written using the >> same version of the compiler, and so if that is not possible then its [quoted text clipped - 5 lines] > >> Peter Drop in replacement without the need to relink the object files/libraries. If you have designed your interfaces properly then you can change the implementation of a class, recompile your dll and swap the old one for the new and bobs your mothers brother. The components do not need to use the same macros and compiler settings other than run-time library. >>> Obviously the components you write should be all written using the >>> same version of the compiler, and so if that is not possible then its [quoted text clipped - 12 lines] > The components do not need to use the same macros and compiler settings > other than run-time library. In that case, you needn't share C++ types with dllimport at all. __declspec(dllimport) is only used when you are sharing not only interfaces, but implementation detail, and then you will need to have compiler settings and macros matching, nor even compiler version. Unless by interfaces, you mean something other than classes consisting of pure virtual methods only. In that case, you are in trouble, because the compiler is placing layout offsets directly into the code on both sides, and they will not match in case macros or compiler settings aren't the same. How can you DllImport a native C++ class in managed code? > Trying to dllimport native C++ classes is a bad idea which will cause you no > end of trouble down the road. I suggest you rearchitect your application [quoted text clipped - 7 lines] > CoCreateInstance to create an instance of the class, probably using the > com_ptr compiler support. SignatureBrowse http://connect.microsoft.com/VisualStudio/feedback/ and vote. http://www.peterRitchie.com/blog/ Microsoft MVP, Visual Developer - Visual C# > How can you DllImport a native C++ class in managed code? You can't. I was speaking about __declspec(dllimport), not System::Runtime::InteropServices::DllImportAttribute >> Trying to dllimport native C++ classes is a bad idea which will cause you >> no [quoted text clipped - 11 lines] >> CoCreateInstance to create an instance of the class, probably using the >> com_ptr compiler support. Ah, okay. You're comment "Trying to dllimport native C++ classes is a bad idea..." got me thinking you were talking specifically about importing a class not functions/methods. A physical impossibility as far as I knew... SignatureBrowse http://connect.microsoft.com/VisualStudio/feedback/ and vote. http://www.peterRitchie.com/blog/ Microsoft MVP, Visual Developer - Visual C# > > How can you DllImport a native C++ class in managed code? > [quoted text clipped - 18 lines] > >> CoCreateInstance to create an instance of the class, probably using the > >> com_ptr compiler support. > Ah, okay. You're comment "Trying to dllimport native C++ classes is a bad > idea..." got me thinking you were talking specifically about importing a > class not functions/methods. A physical impossibility as far as I knew... I was talking about the whole class. Using __declspec(dllimport), from C++ (native) into C++ (native or managed). It is impossible with P/Invoke, which also uses the token dllimport, but is not at all related. >> > How can you DllImport a native C++ class in managed code? >> [quoted text clipped - 24 lines] >> >> the >> >> com_ptr compiler support. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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