Re: [Swig-user] Wrapping C++ class member variables

[Nathan P. <kr...@wa...>]

Any comments or suggestions on this?

Thus spake Nathan Poznick:
> I've got a situation where I want to wrap a C++ class which has member
> variables.  The target language is Perl, although I don't know if my
> issue is specific to it.  For discussion purposes, I have the following
> class defined:
>=20
>     #include <string>
>     #include <list>
>     class Testing {
>         public:
>             Testing();
>             ~Testing();
>             std::list<std::string> foo_func();
>             std::list<std::string> foo;
>     };
>     Testing::Testing() {
>         foo.push_back("list entry 1");
>         foo.push_back("list entry 2");
>     }
>     Testing::~Testing() { }
>     Testing::foo_func() {
>         return this->foo;
>     }
>=20
> I then create the following wrapper input file:
>=20
>     %Module Testing
>=20
>     %include "std_string.i"
>     %include "std_list.i"
>=20
>     %{
>     #include <string>
>     #include <list>
>     #include "Testing.h"
>     %}
>=20
>     namespace std {
>         %template (TestingList) std::list<std::string>;
>     }
>=20
>     %include "Testing.h"
>=20
> I generate the Perl wrapper and compile the shared object,
>=20
>     swig -perl5 -c++ Testing.i
>     g++ -shared -o libTesting.so -I. `perl -MExtUtils::Embed -e ccopts`
> Testing_wrap.cxx
>=20
> I have the following simple perl script to test it:
>=20
>     use Testing;
>     my $test =3D new Testing::Testing;
>     my $list_ret =3D $test->foo_func();
>     foreach my $e (@$list_ret) {
>         print "$e\n";
>     }
>=20
> So far, so good.  When returning a std::list from a class method, it
> properly gets turned into a Perl array ref, and I can access the
> results.  However, if I try to access the member variable directly, I
> run into problems.  Printing it out directly indicates that it's being
> treated as a TestingList perl object.
>=20
>     print "$test->{'foo'}\n";
>=20
> gives:
>=20
>     Testing::TestingList=3DHASH(0x81x66ec)
>=20
> Well, I can understand that.  The object is basically useless to me
> though, unless there's something I'm missing - it only has size(),
> empty(), clear(), and push() methods - no way to actually access the
> contents.  I thought perhaps I could use the auto-generated _get method
> to grab it instead, thinking it would perhaps to the conversion the same
> way as when the list is returned from a method.
>=20
>     my $list =3D Testingc::Testing_foo_get($test);
>     print "$list\n";
>=20
> But nope, that gives me the same thing as accessing it directly.  From
> there I thought that perhaps I needed to define some typemaps for the
> list.
>=20
>     %typemap(out) std::list<std::string> {
>         /* Perlguts voodoo to convert a list of
>            strings to an array goes here */
>     }
>     %typemap(memberin) std::list<std::string> {
>         /* Perlguts voodoo to convert an array to
>            a list of strings goes here */
>     }
>=20
> Yet, I ran into a problem - when I look at the generated
> Testing_wrap.cxx file, the typemap I define for out gets inserted into
> _wrap_Testing_foo_func() (which was working fine before, I just stole
> the code from it to insert into the typemap).  The memberin typemap gets
> inserted into _wrap_Testing_foo_set() as you would expect.  Yet, I'm
> left with _wrap_Testing_foo_get() *not* using the out typemap.  If I can
> affect the _set() method using the memberin typemap, but not affect the
> _get() method with an out typemap, how do I accomplish what I need to
> do?
>=20
> I did some quick testing and manually inserted my output typemap into
> the generated _wrap_Testing_foo_get() function, and after compilation it
> worked as I would expect - by calling Testingc::Testing_foo_get($test)
> from my perl script I could get a proper perl array ref back, and
> iterate over the list as expected.

--=20
Nathan Poznick <kr...@wa...>