Re: [Mingw-users] New User: HOW-TOs for mingw and linking to a DLL

[Mumit K. <khan@NanoTech.Wisc.EDU>]

On Tue, 24 Jul 2001, Chris Marshall wrote:

> Gang -
> 
> I need to be directed towards the HOW-TO's for mingw. Particularly, the 
> question I need answered is how do I compile a C program which uses someone 
> else's DLL that I don't have access to the source code for? I have the .H 
> file, and I have a .LIB file, and I have the .DLL. How do I put all these 
> pieces together?
> 
> I've tried:
> 
> gcc -I./inc -L./lib hello_psft.c psmsg.dll

This is of course the right thing to do, but since you're linking directly
to a DLL (note that this is GNU extension, and, as far as I know, not 
supported by any of the other compiler vendors on Windows), there are some
pitfalls. I believe Danny Smith explained it a while back in a different
thread.

> And I get all sorts of "undefined reference" messages. I assume that somehow 
> I've got to tell the compiler to use the vendor supplied DLL, I just don't 
> know how to do that.

If I remember your original problem, the unresolved symbols had '@' in the
name, which means that these are functions using stdcall/pascal calling
convention. If your DLL exports stdcall symbols, and especially if there
is symbol aliasing going on via the export definition file, you really
can't link directly to a DLL -- you'll have no choice but to create an
import library. 

Here's a quick test: compile the file hello_psft.c and look at the symbols
(pick one that is unresolved after you try to link).

  $ gcc -c -I./inc hello_psft.c
  $ nm hello_psft.o | grep <YOUR_SYMBOL_NAME>

Now look at the symbols that your DLL exports:
  
  $ objdump -p psmsg.dll  | less
  [ Scan for the section "[Ordinal/Name Pointer] Table" and you'll find
  the list of names ]

Now see if there's a match between the two.

My suggestion -- create an import library and just use it. I assume you
have an import library for some other compiler, and if so, it shouldn't
be difficult to create one for GCC. Perhaps easier said than done.

Regards,
Mumit