From: 'Bill Hart' via mpir-devel
Sent: Saturday, June 20, 2015 12:46 AM
To: mpir-devel
Subject: Re: [mpir-devel] Re: MPIR MinGW installation - "undefined reference
to '_imp____gmpz_init'
>I've built mingw-compatible import libs from dynamic libs in the past
>with:
gendef xxxx.dll (creates xxxx.def)
dlltool --kill-at --input-def xxxx.def--output-lib libxxxx.a
[snip]
So that second line creates a .a file?
Yes - it produces an import library (or "stub library", as Brian called it)
for the given dll.
I can't see that as a necessary step in the creating of a dynamic library
for use on Windows. Are you sure this step is required/correct?
Normally it's not needed, as the process that built the dll usually also
builds the import library.
But if you happen to have a dll without an accompanying import library, then
the above allows you to create the import library using only the dll. (I
think there are other convenient ways, in addition to gendef, of creating
the def file.)
As Brian said, it's possible to link directly to the dll, but most build
processes (eg configure scripts, cmake) will be looking for the import
library, rather than the dll itself. And it's generally far easier to create
the import library (if you don't already have it) than it is to modify that
build process such that the import library is not needed.
At runtime, of course, only the dll needs to be found.
With MinGW, both static and import libraries will have the ".a" extension.
Often, the import library is named ".dll.a" - ie "libxxxx.a" being a static
library, and "libxxxx.dll.a" being the import library for the dll.
And "-lxxxx" will enable linking to either the static or import library.
(Not sure which gets found first - I'm guessing it looks for the static
library before looking for the import library.)
IIRC, MinGW used to (and may still) look for ".lib" files. So "-lxxxx" would
seek out an appropriately named ".lib" file if no appropriately named ".a"
file could be found.
I've definitely mixed msvc-built libraries with mingw (and vice-versa, I
*think*) in the past, but that was before gcc-4.x.x, and before 64-bit mingw
compilers, and I can't remember whether it involved static libs, import
libs, or both.
(And it certainly didn't involve C++ libraries.)
Cheers,
Rob
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