Re: Creating and using a Libray

Goran <>
Mon, 15 Mar 2010 05:36:49 CST
On Mar 12, 9:11 pm, Xavier Pegenaute <> wrote:


I am trying to create a library and distribute the library as a .so
file and a simplified header (without private data). I prepared a
basic example (see below).

The setter shows a segfault.

Maybe this is not the right way to do it? Any one knows what's wrong

Well, you made one class inside your .so, but "exported" another. How
exactly did you expect this should work at all?

What you need to do, instead, is e.g. this:


struct test_interface
   virtual ~test_interface() = 0;
   virtual const /*this const is useless, BTW*/ int get_testNumber()
const = 0;
   virtual void set_testNumber(int value) = 0;

extern test_interface* create_it(params);

// actual implementation here,
// with your vector and whatnot.

class test_impl : public test_interface
// .........

test_interface* create_it(params)
   return new test_impl(params);

In other words, don't cheat, there's no need. Use an abstract base
class instead.

Note that by doing this, you are effectively limiting users of your
library to one C++ compiler, and maybe even one version of it. So if
your target user base is wider, you should prepare yourself to compile
with other compilers/versions. Your users also must know what kind of C
++ runtime your library is using (standalone *.lib, or an *.so) and
they must use the same. If not, operator delete might not work
properly, because your *.so expects objects to be freed from it's
heap, which might not be the heap seen by the client code (basically,
a bad "free" function might inadvertently be called). If you don't
like handling all these issues, you should use pure C interface, not a
C++ one. That is constraining, but will also allow use outside C and C+
+ world (that is because every language out there has a foreign
function interface, a.k.a FFI, that can call C functions).

Also, try running your code with something like valgrind. That will
show a lot of errors you might be making.


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