Re: [Boost-users] [multi_index] MSVS 2005 visualizers?

Joaquín Mª López Muñoz (28.5.2007 7:49):

Hello Filip, I did reply this email last Thursday, I guess somehow it didn't make it to your inbox (??) I'm copying and pasting my answer here again:

Filip Konvi?ka ha escrito:

...

Joaquín Mª López Muñoz (23.5.2007 18:16):

...

Hello Filip,

I know nothing about VS visualizers so I'm afraid I can't help much on that part, but feel free to ask as much as you need on the internal structures of B.MI --publicly of privately if you feel this is going to be a long list of mails.

[I tried replying to your email address, but I don't know whether this ever reached you, so I retry here...]

I tried some debugging with multi_index_container > >, which is probably the simplest case. I ended up in the "space" member of "pod_value_holder", which seems to handle some alignment issues and from the name I guess it should also contain the data, but I don't see it in the debugger.

That "space" member is used as raw storage upon which the value (of type int in this case) is constructed. So, you have to reinterpret_cast to get to your value. Does the visualizer allow you to do that?

Yes, but if you look at the screenshot, you see that the space (resp. space.data_.buf) is filled with 0xcd = -51 (i.e. uninitialized) values. If I reinterpret the space member as int, I get 0xcdcdcdcd. So my conclusion is that I'm looking at the "rear" node and I need to go to the prior_ or next_ node, right? So I tried next_, but I got garbage again, but this time it is not 0xcdcdcdcd but something a bit different. I have inserted a "1" into the container, so I'd expect that the buffer contained [0x01 0x00 0x00 0x00]. See screenshot - the expression shown is (sorry :-))) (boost::multi_index::detail::index_node_base<int>*)(&(((*(boost::multi_index::detail::sequenced_index_node_impl*)(&(*(boost::multi_index::detail::sequenced_index_node_trampoline

*)(&*(((*(boost::multi_index::detail::header_holderboost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,b... ,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na,boost::mpl::na>,std::allocator<int>

...

*)(&x))).member)))))).next_))

which in short is that the "next_" member from the previous screenshot is cast to boost::multi_index::detail::index_node_base<int>. The int value in the "space" member is 0x003aa06c.

...

As for sequenced_index_node_impl, this shows both _prior and _next, but does not expose node data. See the attached snapshot. Do you have an idea how could I see the one int that I inserted into the container?

Nodes of a multi-index container consist of several base classes each providing some part of the whole: the value (index_node_base) and pointers for each of the indices (one sequenced_index_node_impl in this case, as there is only one sequenced index.) In schematic form, the node you're deaing with now has the following structure:

struct index_node_base { int value; };

struct sequenced_index_node_impl { sequenced_index_node_impl* prior_; sequenced_index_node_impl* next_; }

struct node_type: public index_node_base, public sequenced_index_node_impl { };

So when you navigate through the sequenced index using prior_ and next_ pointers, you've got to down cast to node_type to get to the values.

Is it clear (more or less)?

Yes, thanks. Cheers, Filip