Passing Arrary and Types to Dlls by Ref

[Mike Trader]

How do I Declare an array in the calling .EXE and the DLL so that I can change array (or TYPE) values at either end ?

Ie pass an array to a DLL that reads some fields and then adds some fields. Then have the added fileds available to the EXE that called the DLL.



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Kind Regards
Mike

[Tom Hanlin]

Variable types are fixed at compile time. There is no way to modify them at run time.
You might consider other approaches, such as storing the data in variable-length
strings or referring to elements by means of pointers. Interpreting the results is up
to you.

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Tom Hanlin
PowerBASIC Staff

[Michael Mattias]

As Mr. Hanlin points out, you cannot change the data type or UDT definition once the program is compiled, but modifying the members of a UDT array should not be a problem:

#COMPILE EXE

TYPE FooType
  member1 AS LONG
  member2 AS LONG
END TYPE

DECLARE FUNCTION UpdateFoo ALIAS "UpdateFoo" LIB "Foo.dll" (F () AS Footype) AS LONG

FUNCTION WinMain (...

   REDIM Foo (100) AS Footype

   CALL UPdateFoo (Foo())

END FUNCTION

#COMPILE DLL "Foo.DLL"
TYPE FooType
  member1 AS LONG
  member2 AS LONG
END TYPE

FUNCTION UpdateFoo (F () AS Footype) AS EXPORT AS LONG

   IF F(1).Member1 = 2 THEN
     F(1).Member2 = 5
   END IF

...
END FUNCTION

MCM




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Michael Mattias
Racine WI USA
[email protected]

[Cecil Williams]

Mike,

As Tom pointed out, you cannot modify the udt construct
at runtime. You'll need to determine the number of added
elements for the udt at compile time. So just add the amount
you'll need then let the dll do it's thing.

An array, however can be resized (redimmed, oops). If you know
what the base size is, then Redim for the added parts.

One option for the udt approach would be to create a linked-list
of structures (udts). If you know what I'm referring to, then
the number of linked structures is up to you. Basically a
linked-list is a udt with all the elements you require plus a
pointer element to the next structure. That way you can track
the list going and coming, add and delete as required.

Cheers,
Cecil

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