Using DLL's with no reference.

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.
LVL 6
JaymolAsked:
Who is Participating?
 
robert_marquardtConnect With a Mentor Commented:
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.
0
 
JaymolAuthor Commented:
So are you saying that it is 100% impossible to find out this information purely from the DLL?

John.
0
 
raidosCommented:
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
0
[Webinar] Kill tickets & tabs using PowerShell

Are you tired of cycling through the same browser tabs everyday to close the same repetitive tickets? In this webinar JumpCloud will show how you can leverage RESTful APIs to build your own PowerShell modules to kill tickets & tabs using the PowerShell command Invoke-RestMethod.

 
JaymolAuthor Commented:
Okay.  So if I have the DLL(s) and the C header file(s), I can do it then?

John.
0
 
robert_marquardtCommented:
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.
0
 
robert_marquardtCommented:
0
 
MadshiCommented:
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.
0
 
JaymolAuthor Commented:
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.
0
 
robert_marquardtCommented:
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.
0
 
JaymolAuthor Commented:
Thanks guys.
0
All Courses

From novice to tech pro — start learning today.