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edwinnie

dll for functions? classes?

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hey! I was playing around with DLL loading using both the static .lib and dynamic loading using the LoadLibrary. I noticed that i can access classes from the static loading, but i havent figured out a way how to do that for dynamic loading. or is there no such possibility? thx! Edwinz

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for dynamic loading, you theoretically cannot directly instantiate a class object that is defined in the DLL itself. Thats y the static link works: the compiler gets the class definition from the header file of the DLL/LIB.

there is one (half?) workaround. What you can do is define a stub declaration that mimics the class exposed in the DLL. This stub could be an exact duplicate of the original class header, just make sure the function names and parameter signatures and order of declaration is exact. However, you don't need to define the implementation for any of the functions. Just the declaration will do.

What you do next is create a function in the DLL that will create an instance of the particular class. The function should return a pointer to this DLL-local heap variable.

Include the stub header in ur application, load the DLL dynamically, get the address for the 'creator' function and use the function to get the actual object itself.

STUBCLASS *localPtr = Creator();
//NOTE: Since the local definition of the class does NOT define the
//implementation, you cannot instantiate it locally. That's why u use
//the DLL function to create the actual instance.


The stub class is just a means to:
1. Define a name to use for obtaining an object from the DLL
2. To allow your code to be aware of the functions that you can access via the object
This of course implies that you must be fully aware of the class structure, which may not be ideal if the DLL is meant for 3rd party use.

This is a roundabout way though, and may not be ideal for all situations. There is an article on GameDev somewhere about exposing classes in DLLs but i dun have the link right now. Another alternative is to use COM interface, which uses an advanced version of DLL-based allocation and reference counting.

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ah thx alot!
i din noe there was an article here.

ratings+++!

[Edited by - edwinnie on June 22, 2005 4:25:52 AM]

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