This is really very simple:

Step 1: The main program calls an initialization point in the DLL, passing a
pointer to a structure containing the addresses of all the routines of
interest.

Step 2: The DLL uses the pointer to call the routine.

In more detail:

in a header file common to the main code and the DLLs:

typedef struct HelperFuncs {
       void (*one_function)(int something, char another);
       int (*another_function)(void);
    ... etc ...
};

In the main program:

void (*one_function)(int something, char another);
int (*another_function)(void);

struct HelperFuncs  helpers = {
    one_function,
    another_function
};

InitializeDLL( ..., &helpers, ... );

In the DLL:

struct HelperFuncs *hf;

void InitializeDLL(..., struct HelperFuncs &helpers, ... )
{
    hf  = helpers;
}

(hf->one_function)(123,'a');
i = (hp->another_function)();

Bob Ammerman
RAm Systems

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