[Numpy-discussion] C Extensions, CTypes and "external code & libraries
Wed Feb 13 09:38:50 CST 2008
On Feb 14, 2008 12:14 AM, Lou Pecora <email@example.com> wrote:
> --- David Cournapeau <firstname.lastname@example.org>
> > Oh, I may have misunderstood what you are trying to
> > do then. You just
> > want to call a shared library from another shared
> > library ? This is
> > possible on any platform supporting shared library
> > (including but not
> > limited to mac os x, windows, linux, most not
> > ancient unices).
> First, thanks very much for all the information. I am
> still digesting it, but you gave a clear explanation
> about the difference between shared and dynamic
> libraries on the Mac.
> I tried some of your compile/like commands, but the
> Mac gcc did not understand some things like -Bstatic
> and -shared. It seems to want to make bundles. I
> guess your code was a Linux version which the Mac
> doesn't like.
Yes, I forgot that -shared does not work on mac os X. -Bstatic, being
a linker option as I said, had little chance to work on mac os X. But
encouraged by your help, I got the
> # ---- Library make ---------------------------
> mysharedlib.so: mysharedlib.o mysharedlib.mak
> gcc -bundle -flat_namespace -undefined suppress -o
> mysharedlib.so mysharedlib.o \
> # ---- gcc C compile ------------------
> mysharedlib.o: mysharedlib.c mysharedlib.h
> gcc -c mysharedlib.c -o mysharedlib.o
> In the above fcnlib.a is a simple static library I
> made before using the above make. This created the
> shared library mysharedlib.so which I imported and
> handled with CTypes. Calling a function in fcnlib.a
> from python worked.
> A possible downside is that the shared library
> contains *all* of the fcnlib. I examined it using "nm
> mysharedlib.so". That showed that all the functions
> of fcnlib.a were present in mysharedlib.so even though
> the function in mysharedlib.c only called one function
> of fcnlib.a. I don't know how much of a burden this
> will impose at run time if do this with GSL. It would
> be nice to only pick up the stuff I need. But at least
> I have workable approach.
This is logical, or more exactly, the tools did what it thinks you are
asking: putting the archive (the .a library) in your executable. If
instead of libfnclib.a, you just put -lfcnlib in the command line, it
will pick up only the necessary code for the functions you are calling
(at least it does on linux if I remember correctly).
But the real question is : if you are concerned with code bload, why
using static lib at all ? Why not using shared library, which is
exactly designed to solve what you are trying to do ?
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