impdef, msvc++ 6, and GMP

Ike Evans ike at
Fri Nov 7 09:10:54 CET 2003

On 7 Nov 2003 at 12:20, Sisyphus wrote:

> It's just so much nicer and easier if people can simply take the dll and
> build the lib using only msvc++, without having to use any other tool. Of
> course, they already can do that ... if they've got a 'proper' edition of
> msvc++ 6 :-)
Actually, the 'proper' edition of msvc++ 6 doesn't help. The ms knowledge 
base doesn't even mention impdef, but if you run a search using just the 
right terms on a night of a full moon after praying to your favorite 
search engine god you can find knowledge base article 131313 (or, having 
read this post, just search for 131313) which says "There is no 32-bit 
utility that can create an import library from a .DLL, as there was with 
16-bit versions of Visual C++."

131313 describes two workarounds that aren't guaranteed to work. The 
first workaround (hand-building the .def) does work in this case. I 
didn't try the second workaround (building a stub for every gmp 

Here's my version of the process, which may help avoid some pitfalls for 
the unwary. YMMV.

1. Use 'DUMPBIN /EXPORTS libgmp-3.dll' to get a symbol list. Redirect to 
some convenient text file.
1.1. If this is the first time you've used an MSVC++ 6 command line tool 
in awhile, you'll probably need to set up your environment properly. Use 
ms provided Vcvars32.bat to do this (found in the Vc98/bin directory).
1.1.1. If you are running from an ms-dos prompt and run out of 
environment space, increase same by maxing out initial environment space 
in the properties:memory dialog for your ms-dos prompt.
2. Handbuild libgmp-3.def with the symbol list from step 1.
2.1. libgmp-3.def is a text file that looks like:
     LIBRARY libgmp-3
2.1.1. If your goal is to do this with only ms provided tools, you can 
easily extract just the 382 symbols from the output of step 1 by 
importing into excel.
3. Use 'LIB /DEF:libgmp-3.def /OUT:libgmp-3.lib' to create your lib.
4. Put .lib and .dll in appropriate places and add libgmp-3.lib to your 
link list in msvc++ 6 project settings.

I did this successfully using deltatrinity's gmp build (thanks Eric).

BTW, you could avoid having to build a .lib in the first place by using 
run-time dynamic linking to the .dll, but that has a different set of 


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