function pointer problem in COM

[sachin30]

Hi,
I have a com dll and I am using LoadLibrary function for
loading this dll.

After that I want call a createInstance() function.
To call this function I am using a function ptr that got initialized from GetProcAddress() API.

Here I am facing a problem how to initialize this function pointer for CreateInstance()

All i am doing is.
dll name => MyDll
class name =>MyClass

interface name derived from IDispatch(com interface) ==> IMyClassPtr

long (IMyClassPtr::*CreateInstancePtr)(LPCWSTR *name) = NULL;

HMODULE handleMyDll ;
handleMyDll = LoadLibrary(L"MyDll.dll");

CreateInstancePtr = GetProcAddress( handleMyDll,"MyClass::CreateInstance");

if(CreateInstancePtr == NULL)

-when we call GetProcAddress() function it is giving me an error saying cannot convert.

Can any one tell me the syntax for function pointer or
is any thing wrong in GetProcAddress()

Thanks in Advance

[weaknessforcats]

Are you using C++? I think so because of this:

..."MyClass::CreateInstance");

When you use GetProcAddress to get a pointer to "MyFunction", there had better be a function named MyFunction in the library that you loaded.

Unfortunately, to support function overloading, your c++ compiler has mangled MyFunction into some unique id like @FF47skidoo. So that's what's in your library but you are asking for "MyFunction".

You must, without fail, in the library code only, define MyFunction as extern "C". That will tell the C++ compiler to not mangle the name "MyFunction". Now GetProcAddress will work.

However, now you have lost function overloading for MyFunction. Remember, a dll and GetProcAdress are old C structures so they have to be used as C.

My advice is to write interface functions in the DLL coded as extern "C" and have those functions call the real C++ functions. Then you export the interface functions so you can use them with GetProcAddress.

[sachin30]

thx for replay let me check it out.
Just wanted to know is it right way of using LoadLibrary function to load a COM dll.

[weaknessforcats]

Yes you can useLoadLibrary to load any dll. A COM dll is still just a dll. As a fine point I would not hard-code the name of the dll. Get the name dynamically at run-time. What you have is OK for test but not for an actual release.

Usually, you use LoadLibrary when you want to control loading and access to the dll. That is, maybe you want to load the dll and call GetProcAddress on all the functions rght at the start.

Otherwise, you can link the .lib version of the dll at build time. The function in the lib is a dummy function. It calls LoadLibrary and then calls GetProcAddress s you don't have to.

[sachin30]

thanks for detailed information.
In my case LoadLibrary is loading a com dll successfully.
But
the GetProcAddress() function is returning NULL for createinstance().
Can any one point me why is happning or we cannot use GetProcAddress() for com specific createInstance().

[weaknessforcats]

Did you read my Post #2 above?

If so, have you coded your dll functions as extern "C"?