Excel DLLs

Jeff Sturm jsturm@sigma6.com
Tue Mar 7 09:54:00 GMT 2000

Roland Ruehl wrote:
> - Does anybody know about detailed documentation for passing parameters
>         from Visual basic to Cygwin ? For instance, by trial and error,
>         I found out that Strings are passed as pointers to C arrays of
>         shorts, but am wondering about more complex structures, i.e.
>         records, arrays, etc. How do I pass an unknown number of
>         parameters, similar to the Excel SUM() construct, for example ?

Those strings are really BSTR, which are generally equivalent to wchar_t
* (same size as a short, as you found out).  The difference is that they
must be allocated with SysAllocString and released with SysFreeString to
avoid memory corruption.

VBA/Excel rely extensively on the IDispatch (automation) interface,
which defines a special type, VARIANT, for arguments and return values. 
The VARIANT is a large union of all possible automation types.  See the
MSDN docs for more information.
I also find "Inside Distributed COM" from Microsoft Press very helpful.

Jeff Sturm

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