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Using DLL's with no reference.

Posted on 2001-08-15
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Last Modified: 2010-04-06
Hi.

I just wondered how I'd go about using a function in a DLL if I didn't know how it was declared.

For example, if there was a function called 'MessageBox' in a DLL called msg.dll and it needed to be called like this....

   MessageBox('This is the message', 'This is the title');

....how would I know how to do that?  If I opened the DLL within Quickview, for example, it would say that there was a function called 'MessageBox', but not give me any reference on how to use it.

Can anyone help me with this?

John.
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Question by:Jaymol
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robert_marquardt earned 150 total points
ID: 6388560
The DLL does not contain any information on the function parameters.
You will need the documentation.
Normally this is the C header file (.h file) which contains the prototype of the functions.
It also gives the calling convention (usually cdecl or stdcall) of the functions.
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by:Jaymol
ID: 6388573
So are you saying that it is 100% impossible to find out this information purely from the DLL?

John.
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Expert Comment

by:raidos
ID: 6388650
As i have understood it's not possible to get the parameter types from the dll, only the number of parameters and/or the complete size of all the parameters.

I'm not sure of this but this is what my memory tells me...

//raidos
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by:Jaymol
ID: 6388670
Okay.  So if I have the DLL(s) and the C header file(s), I can do it then?

John.
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Expert Comment

by:robert_marquardt
ID: 6389643
With the C headers it is no problem at all.
Post some function headers here and i will help you convert them to Pascal.
Also have a look at http://dlephi-jedi.org page 'API Library'.
We specialize in converting C headers to Pascal.
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by:robert_marquardt
ID: 6389648
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by:Madshi
ID: 6391557
If you have no C(++) headers, you could still try to reverse-engineer (disassemble) the dll. I'm not sure whether this is allowed  :-)  but, well, that's a different story. By disassembling the dll's code, you can find out how many parameters the function wants and - if you completely disassemble the function and understand it fully, you'll most probably also find out what the parameters mean. But I have to warn you: This is very very very hard work. You should do that only as the very last resort. If you have ANY chance to get a C(++) include file: Use that chance...

Regards, Madshi.
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by:Jaymol
ID: 6391651
Thanks Madshi, but I'm not going down the route you've mentioned since you're probably the only person that comes on this site capable of doing something like that!  I did disassemble it, rather than using Quickview, to see the funcs/procs and it did give me more information, but I've "aquired" the C++ files so (as suggested by Robert) I can attempt a conversion.  There's probably gonna be a lot of C to Pascal points going from my account soon!

I'll have a look into my options and get back to do pointy things.

Thanks guys.

John.
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by:robert_marquardt
ID: 6391934
Project JEDI has many C to Pascal specialists (and i am one of them :-)
Please send me the headers to robert_marquardt@gmx.de and i will have a look.
C++ headers may be problematic if C++ methods are exported.
C++ methods are unusable in Delphi.
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by:Jaymol
ID: 6421222
Thanks guys.
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