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Message-ID: <3BE80EAC.50400@ece.gatech.edu>
Date: Tue, 06 Nov 2001 11:24:12 -0500
From: Charles Wilson <cwilson AT ece DOT gatech DOT edu>
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To: David Westbury <David DOT Westbury AT ipaper DOT com>
CC: cygwin AT cygwin DOT com
Subject: Re: DLL's for Dummies
References: <OF277487F1 DOT DD007F3A-ON85256AFC DOT 004B9C63 AT ipaper DOT com>
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Where are you getting the declarations of the functions within the dll 
(e.g. the header files)?  It sounds like myprog.o is getting compiled 
without declaring the functions/variables imported from the DLL as 
"__declspec(dllimport)".  This omission *could* cause the problems you are 
seeing.

If you are using "MSVC-ish" header files that came with your third party 
DLL, you *MAY* need to rewrite them somewhat for use with cygwin.

--Chuck

David Westbury wrote:

> I recently got started with Cygwin. What a great package! Coming from a
> Unix programming background I'm completely in the dark about DLL's. I need
> to write C programs that access a third party API. I'm experimenting with
> gcc but having disappointing results. I'm trying to compile and run an
> example C program that came with the third party API package. Although I
> don't know how to compile a program against a DLL I've found that the gcc
> string below results in an error free compile/link. The resulting
> executable runs to some degree. Some API calls execute correctly. However
> using the gdb debugger it appears that random memory locations are being
> modified as I step through the program. The program employs elements of a
> structure as arguments to the API calls. The debugger shows that, in
> addition to modifying the correct structure elements, random elements of
> the structure are also being modified as I step over many of the API calls.
> Also memcpy() appears to produce similar memory corruption. I'm hoping this
> will ring a bell with someone who can guide me in the right direction.
> 
> Here is the gcc string I'm using:
> 
> gcc  -g   myprog.c  -o myprog   /path to third party dll/api.dll
> 
> I've been working with this for days.  Forgive me if I haven't read the
> right FAQ or documentation. I've scanned about everything I can find. Any
> help would be greatly appreciated. Thanks.
> 
> 
> 
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