Comments:	Authenticated sender is <chrism AT mail DOT compusmart DOT ab DOT ca>
From:	"Chris Martyniuk" <Chris DOT Martyniuk AT compusmart DOT ab DOT ca>
To:	DJGPP AT sun DOT soe DOT clarkson DOT edu
Date:	Wed, 22 Nov 1995 00:03:36 +0000
Subject:	Linking and calling functions dynamically at runtime
Reply-To:	chrism AT compusmart DOT ab DOT ca

This question might be better suited to a generic dos programming 
forum, but you guys might be able to offer some insight into my 
problem.

I need a way to load code into memory and then call these functions
dynamically at run time, without prior knowledge of their function 
names, etc...

A project I'm involved in consists of a number of 'features' that
make up the functionality of the program.  Generally, each feature
consists of a number of elements, and a common function to implement
these elements.  (Ie, a number of palettes [the elements] and a
function to load the palette into the RAMDAC of the VGA card [the
feature function]).  

For most features, loading these elements is easy - set up an array
of pointers to buffers that are created when reading the element
data from disk.  This approach works for 8 out of 10 features.

However, for the other 2 features, each element is itself a separate 
function.  I need some way of being able to load these functions into 
memory, set up a pointer to the function, and call it - all 
dynamically at runtime.  

I could prepackage all the functions into a separate module, and
keep a master list of pointers to them and then select from this
list instead of loading from disk, however that limits me from being
able to send 'feature upgrades' to the end user.  Ie, here's a file 
with more elements for Feature X.

One approach I've thought of is to create a DLL with 100 function 
entries (or whatever maximum number) then test each of these 
functions for existance when the program initializes.  Thus, I will 
be able to create my 'master list' of feature elements and be able to 
select from this list in forming my enable feature element list.

The drawback to this approach is that I'll have to release the new
elements in 'clumps', rather than as individual files.

So, back to DJGPP - does it allow for DLLs or overlays??  Is there a 
better approach to accomplish what I need to do??  

Any suggestions are GREATLY(!) appreciated!

Thanks,
Chris .\\

PS:  The element functions are very small and will all typically
access the same areas of memory, etc...  They will also generally
not make calls to other functions in the program. 

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