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Classes in Dll

Posted on 1997-05-16
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Last Modified: 2010-04-04
I have a class build in c++ in a Dll.
Can anyone tell me how can i use it in delphi 2.0?
Thank you.

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Question by:Nuno Alves
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sperling earned 100 total points
ID: 1336344
Create a similar virtual and abstract class in delphi 2. Get the address of a instance of the C++ class, and cast this address to the delphi class.


e.g.

type

  TClassCorrespondingToDllClass = class
    function FirstMethodInCPPClass : INTEGER; stdcall; virtual; abstract;
    procedure SecondMethodInCPPClass; stdcall; virtual; abstract;
  end;


Then

var
  TheObject : TClassCorrespondingToDllClass;

begin
  TheObject := TClassCorrespondingToDllClass ( DLLFunctionCreatingTheClassAndReturningPointer)

  TheObject.SecondMethod;
end;

If your delphi class maps *exactly* to the c++ class (calling convention and parameters), this should work. You need to have the DLL create an instance of the class though.

Regards,

Erik.
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Author Comment

by:Nuno Alves
ID: 1336345
How can I load the dll in delphi?
I now that with the dll in C I just have to put before
the declaration of the function external 'Dll name' but
with the class i couldn't do the same.
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Expert Comment

by:sperling
ID: 1336346
You have to declare an exported function in the C DLL. This function should create an instance of the class and return it as a pointer. I can't be of much help when it comes to C syntax...

Import it into delphi like this:

function CreateAnObject : POINTER; stdcall; external 'DLLNAME.DLL' name 'ExportedNameOfCreateAnObject';


Regards,

Erik.
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