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RE: [Boost-Users] Iterator adapters and maps
by scleary＠jerviswebb.com 04 Oct '02

04 Oct '02

I think the problem is in the definition of Select2ndRef; if you use: template<class pair_type> struct Select2ndRef { typedef pair_type argument_type; typedef typename pair_type::second_type result_type; result_type & operator()(pair_type & source) const { return source.second; } }; then your code will compile. This has to do with an unusual meaning of "result_type" for projection iterator adaptors. -Steve

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Use a shared_ptr as a 'backpointer'?
by dick.bridges＠tais.com 04 Oct '02

04 Oct '02

I run into situations where it's useful for an object to have a 'backpointer' to the object instance that created it (example below). Is there a pattern/idiom for doing this using shared_ptr? Or maybe I need to re-think the idea of the backpointer in the first place? class Bar; class Foo { public: Foo(Bar* b) : p(b){} private: Foo() : p(0){} shared_ptr<Bar> p; } class Bar { void doit() { new Foo(???); // <<< new Foo(this) obviously won't work. } }

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[BGL]: 2 desgin questions
by Björn Lindberg 03 Oct '02

03 Oct '02

I have two questions regarding the design of the BGL. I'm interested in this to get a better understanding of the design choices, which influences how I use the BGL and how I'm building on it. 1) Why is a lot of the function arguments made by value rather than reference? As an example, consider the BFS algorithm, where the documentation states that "[1] Since the visitor parameter is passed by value, if your visitor contains state then any changes to the state during the algorithm will be made to a copy of the visitor object, not the visitor object passed in. Therefore you may want the visitor to hold this state by pointer or reference." It would be much easier to use the visitor objects for keeping state throughout the algorithm if it was passed by reference instead. 2) Non-constness. It seems impossible to use BGL together with code that is "const-correct". If, for instance, I have a function implementing some kind of examining algorithm on a graph (so the graph is passed to it as const), and this algorithm uses breadth_first_search with a visitor that doesn't modify the graph, it still can't be const when passed to breadth_first_search. This only leaves the options of either (i) casting away constness in the call, which is bad because it could introduce bugs later on, or (ii) leaving out const altogether which is not good either. Maybe I've just misunderstood something and this is possible, or perhaps it is impossible to implement BGL in this way? Björn

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boost build on redhat7.3
by Alkis Evlogimenos 03 Oct '02

03 Oct '02

Hi, I just compiled boost from cvs. I am using an x86 with redhat linux 7.3. I also have STLport 4.5.3 installed. I compiled against STLport using this command: bjam "-sTOOLS=gcc-stlport" "-sSTLPORT_INCLUDE_DIRECTORY=include/stlport" "-sSTLPORT_LIB_DIRECTORY=lib" "-sSTLPORT_ROOT=/usr" and against gcc using the following: bjam "-sTOOLS=gcc" Both builds finish with success (compiling with j4 leaves 2 targets behind but they succeed after a reinvocation). Now I enter status/ and compile regression using the following: g++ -I.. regression.cpp -o regression Modify compiler.cfg to look like: linux gcc-296 GCC 2.96 g++ -c -Wall -W -ftemplate-depth-30 -I%include %source g++ -o boosttmp.exe -Wall -W -ftemplate-depth-30 -I%include %source -lrt GNU <a href="http://gcc.gnu.org/">GCC</a> 2.96 linux gcc-296-stlport GCC 2.96 STLport 4.5 g++ -c -Wall -W -ftemplate-depth-30 -isystem /usr/include/stlport -I%include %source -lstlport_gcc g++ -o boosttmp.exe -Wall -W -ftemplate-depth-30 -isystem /usr/include/stlport -I%include %source -lrt -lstlport_gcc GNU <a href="http://gcc.gnu.org/">GCC</a> 2.96 <a href="http://www.stlport.org/">STLport</a> 4.5 and finally run regression as follows: ./regression -o cs-rh7.3.html Attached is a gzipped log of the regression run. The text was 429Kb so I didn't paste it to this email :-) It seems that the testing frameworks has some problems (libs/config/test/config_test.cpp fails). Am I doing something wrong here? Any help is appreciated. Thanks, -- Alkis [Non-text portions of this message have been removed]

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[BGL] Daisy chaining algorithms using vistor mechanism?
by Chris Russell 02 Oct '02

02 Oct '02

Still up hacking... Without cluttering the question with a ton of detail, basically I need to perform a DFS on a forest stored in a bidirectionalS adjacency_list and then perform a subgraph traversal in response to each finish_vertex invocation in the visitor. (The idea is to push information down the branches towards the root of a tree in the forest). Calling in_edges(v,g) from within the finish_vertex method in a dfs_visitor will not compile however. This is because the graph is passed by const reference into the visitor method and in_edges requires a non-const graph reference? (this seems similar in spirit to a question I posted a week or two ago about boost::get(some_property, Graph) from within a visitor). Generally, I would like to be able to daisy chain graph algorithms - that is invoke a sub-algorithm from within a visitor method called by a controlling algorithm. This would require that the sub-algorithm not change the graph topology, trample on properties used by its controller (e.g. coloring), or otherwise invalidate vertex descriptors or iterators so some care would need to be taken in designing the sub-algorithm. But it seems like a useful mechanism for extension. Am I missing something about getting at the in_edges given that I'm working with a const graph_t& in the context of the "controlling" DFS' visitor method? Why is this so restrictive? I'm guessing it might have something to do with having multiple copies of vertex and edge iterators floating around but I'm not sure. Will you comment on this please Jeremy? Thank you. - Chris Russell

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RE: [Boost-Users] MPL?
by Mark Storer 02 Oct '02

02 Oct '02

"Modern C++ Design" has a pretty good coverage so far (I'm on chapter 6 out of 11). As for impressing the ladies... well... you could always show them your stamp collection. --Mark Storer Software Engineer Cardiff Software #include <disclaimer> typedef std::disclaimer<Cardiff> Discard; -----Original Message----- From: Jeff Faust [mailto:jeff@opticalres.com] Sent: Wednesday, October 02, 2002 12:37 PM To: Boost-Users(a)yahoogroups.com Subject: RE: [Boost-Users] MPL? Well, I didn't know I needed boost until I saw it. Same for STL several years back. 'Metaprogramming' comes up a lot on the boost list, but I have no understanding about what it's for--what problems it solves. The documentation is sparse. Then this thread comes up and everybody talks about it like it's obvious. I dislike being baffled. But mostly it's curiosity. I need something to talk about at parties and impress the ladies. MPL will do that, right? Right? Hello? Jeff -----Original Message----- From: David B. Held [mailto:dheld@codelogicconsulting.com] Sent: Wednesday, October 02, 2002 12:14 PM To: Boost-Users(a)yahoogroups.com Subject: Re: [Boost-Users] MPL? ----- Original Message ----- From: "Jeff Faust" <jeff(a)opticalres.com> To: <Boost-Users(a)yahoogroups.com> Sent: Wednesday, October 02, 2002 11:32 AM Subject: [Boost-Users] MPL? > [...] > Can anybody explain in English what the following does? I believe that Aleksey posted the runtime pseudo-equivalent. > Posted by David Abrahams on boost developers list: > > Have I mentioned recently how totally cool MPL's lambda facility is? > > I can't believe I can do things like this, even with MSVC6. It makes my > > metaprograms SO much easier to manage! > > mpl::logical_and< > > is_reference_to_class<add_reference<mpl::_> > > > , mpl::logical_not< > > is_reference_to_args<add_reference<mpl::_> > [Aleksey, on 9/27] // "ideal" version, for comparison purposes: // is_reference_to_class( add_reference(_) ) // && !is_reference_to_args( add_reference(_) ) I can't say for sure what the code does myself, but if I could venture a guess, I would say that it's a condition for something else (maybe an iterative algorithm over a type container?) that checks to see if an argument is a reference type of various sorts. Basically, if you don't understand it, in this case, you probably don't need it. ;) I know I don't! Dave Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

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RE: [Boost-Users] MPL?
by Randy Bowen 02 Oct '02

02 Oct '02

Metaprogramming techniques are discussed pretty thoroughly in Andrei Alexandescru's "Modern C++ Design" and in Czarnecki and Eisenecker's "Generative Programming". --Randy -----Original Message----- From: Jeff Faust [mailto:jeff@opticalres.com] Sent: Wednesday, October 02, 2002 12:37 PM To: Boost-Users(a)yahoogroups.com Subject: RE: [Boost-Users] MPL? Well, I didn't know I needed boost until I saw it. Same for STL several years back. 'Metaprogramming' comes up a lot on the boost list, but I have no understanding about what it's for--what problems it solves. The documentation is sparse. Then this thread comes up and everybody talks about it like it's obvious. I dislike being baffled. But mostly it's curiosity. I need something to talk about at parties and impress the ladies. MPL will do that, right? Right? Hello? Jeff -----Original Message----- From: David B. Held [mailto:dheld@codelogicconsulting.com] Sent: Wednesday, October 02, 2002 12:14 PM To: Boost-Users(a)yahoogroups.com Subject: Re: [Boost-Users] MPL? ----- Original Message ----- From: "Jeff Faust" <jeff(a)opticalres.com> To: <Boost-Users(a)yahoogroups.com> Sent: Wednesday, October 02, 2002 11:32 AM Subject: [Boost-Users] MPL? > [...] > Can anybody explain in English what the following does? I believe that Aleksey posted the runtime pseudo-equivalent. > Posted by David Abrahams on boost developers list: > > Have I mentioned recently how totally cool MPL's lambda facility is? > > I can't believe I can do things like this, even with MSVC6. It makes my > > metaprograms SO much easier to manage! > > mpl::logical_and< > > is_reference_to_class<add_reference<mpl::_> > > > , mpl::logical_not< > > is_reference_to_args<add_reference<mpl::_> > [Aleksey, on 9/27] // "ideal" version, for comparison purposes: // is_reference_to_class( add_reference(_) ) // && !is_reference_to_args( add_reference(_) ) I can't say for sure what the code does myself, but if I could venture a guess, I would say that it's a condition for something else (maybe an iterative algorithm over a type container?) that checks to see if an argument is a reference type of various sorts. Basically, if you don't understand it, in this case, you probably don't need it. ;) I know I don't! Dave Info: < http://www.boost.org> Wiki: < http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ Yahoo! Groups Sponsor ADVERTISEMENT <http://rd.yahoo.com/M=233351.2428261.3848243.2225242/D=egroupweb/S=17050067…> <http://us.adserver.yahoo.com/l?M=233351.2428261.3848243.2225242/D=egroupmai…> Info: < http://www.boost.org> Wiki: < http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service <http://docs.yahoo.com/info/terms/> . [Non-text portions of this message have been removed]

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Iterator adapters and maps
by Alisdair Meredith 02 Oct '02

02 Oct '02

I have a std::map<std::string, MyObject> and want to iterate over it calling several member functions of MyObject. This seems like a good case to learn about transform/projection iterator, but I am having a hard time getting a compiling example. My most recent attempt looks like this: class MyObject { public: void CommitChanges(); void RollbackChanges(); // More implementation details would follow }; typedef std::map<std::string, MyObject> MyMap; typedef MyMap::iterator MyIterator; typedef MyMap::value_type mapped_type; typedef boost::projection_iterator_generator< Select2ndRef<mapped_type>, MyIterator >::type projection; MyMap theMap; projection begin( theMap.begin() ); projection end( theMap.begin() ); for_each( begin, end, mem_fun_ref( MyObject::CommitChanges ) ); I also have the following two templates, although I suspect their equivalent must be lurking in boost somewhere: template<class pair_type> struct Select1stRef { typedef typename pair_type::first_type & result_type; result_type operator()( pair_type &source ) const { return source.first; } }; template<class pair_type> struct Select2ndRef { typedef typename pair_type::second_type & result_type; result_type operator()( pair_type &source ) const { return source.second; } }; I am compiling using BCB5 compiler in the IDE, should be equivalent to the free 5.5.1 command line compiler. While I could simply write a forwarding functor in a fraction of the time it will take me to solve this, there is definitely a ne tool I would like to add to my toolbox here once I understand what is happenning. Unfortunately I am getting somewhat lost in reference-to-reference issues, and the occasional compiler crash does not help. Any and all hints appreciated -- AlisdairM

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Loki vs. Boost
by Hamlet 02 Oct '02

02 Oct '02

Hi, I'm (desperately) looking for a serious comparative review of Loki vs. Boost libraries. Although the differences are quite clear, still it would be nice to see a serious comparison, especially in the features that exists in both places, i.e. smart pointers, small obj. allocator, type traits and template meta-programming. Does anybody knows if there exists such a paper somewhere, or alternatively have his own insights about the libraries? Thanks, Ariel

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[BGL] vertex_index_t w/VertexList=listS questions
by Chris Russell 02 Oct '02

02 Oct '02

Hi Jeremy, Using adjacency_list w/VertexList=listS, I've stuffed a vertex_index_t declaration into the internal vertex property map and got my DFS invocation to compile. Taking a look at the dijkstra-example-listS.cpp in the examples directory on CVS, I see how you manually initialize this property for each of the vertices after you build up the graph. p.230 of the book discusses the auto-update of the vertex_index_t property upon vertex removal for the case of VertexList=vecS but I'll need to affect this update myself for VertexList=listS? Also, can you foresee any problems if I register vertex_index_t with a value_type of long int instead of int? I'm guessing no because I'm passing it as a template parameter but I just want to make sure. - Thanks and regards Chris Russell

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