July 2002 - Boost-users - lists.boost.org

Re: [boost] Re: Iterator Adaptor Poll
by David Abrahams 26 Jul '02

26 Jul '02

From: "Gennadiy Rozental" <rogeeff(a)emailaccount.com> > BTW, you may consider CycleIteratorAdaptor or JoiningIteratorAdaptor. They > both really simple and illustrative. No simpler than the transform adaptor, though? As I've repeatedly posted, I think any introductory example ought to build a simple iterator, not an adaptor. -Dave ----------------------------------------------------------- David Abrahams * Boost Consulting dave(a)boost-consulting.com * http://www.boost-consulting.com

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RE: [Boost-Users] Re: [boost] Iterator Adaptor Poll
by Elliot Murphy 26 Jul '02

26 Jul '02

I really like that example iterator (I was just typing up an email to suggest it when I received this one). The example does something useful, and you can easily see the difference between reading lines of input without the iterator, and with the iterator. The comment on page 5 of that book really emphasizes just how much this example would benefit from using iterator_adaptor "Don't worry if you don't yet understand why everything in the line_iterator class is there; parts of it are only necessary for technical reasons." -elliot -----Original Message----- From: Jeremy Siek [mailto:jsiek@cs.indiana.edu] Sent: Friday, July 26, 2002 10:29 AM To: Boost-Users(a)yahoogroups.com Cc: boost(a)lists.boost.org Subject: Re: [Boost-Users] Re: [boost] Iterator Adaptor Poll Here's another idea for a "hello world" example. A rewrite of Matt Austern's line_iterator example from his Generic Programming and the STL book. The line_iterator call getline() and then return a std::string from operator*. On Fri, 26 Jul 2002, David Abrahams wrote: dave> dave> That's neat, but we already have the permutation adaptor, and I dave> don't think it's really a simple enough example. Beman's example dave> just makes a simple iterator, not an adaptor, and I think that's an dave> important feature for a "hello, world"-type introduction. dave> dave> -Dave ---------------------------------------------------------------------- Jeremy Siek http://php.indiana.edu/~jsiek/ Ph.D. Student, Indiana Univ. B'ton email: jsiek(a)osl.iu.edu C++ Booster (http://www.boost.org) office phone: (812) 855-3608 ---------------------------------------------------------------------- Yahoo! Groups Sponsor Click here to find your contact lenses! 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.

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RE: [Boost-Users] Fw: [boost] Iterator Adaptor Poll
by Hickman, Greg 26 Jul '02

26 Jul '02

> -----Original Message----- > From: David Abrahams [mailto:dave@boost-consulting.com] > Sent: Thursday, July 25, 2002 4:00 PM > To: Boost-Users(a)yahoogroups.com > Subject: [Boost-Users] Fw: [boost] Iterator Adaptor Poll > > > Hi Everyone, > > Have you tried to use iterator adaptors and found the documentation > wanting? I have recently updated the documentation in the CVS: > http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/*checkout*/boos > t/boost/libs/ > utility/iterator_adaptors.htm?rev=HEAD > > However, enough people have had problems approaching this > library that I > thought it would be useful to ask about what would make a gentle > introductory example. Beman recently sent me the enclosed, > but it seems to > define such an oddball toy iterator that I'm not sure it > would be a very > good motivating example. I'm asking for input, especially > from anyone who > has "gotten over the hump" so to speak, with iterator adaptors. I'm brand new to iterator_adaptors, and this is probably way too trivial an example, but I have several classes in my project which aggregate other polymorphic objects in part-whole relationships. I'd like clients who call 'the_aggregate.begin()' to be able to call non-const methods on the aggregate's Parts, but I'd like to prevent direct replacement of the underlying container element 'Part*' itself. Likewise, I'd like clients who call 'the_aggregate.begin() const' to be prevented from doing anything with the aggregate's Parts other than calling it's const methods. Of course, the STL container-supplied iterators aren't intended to work in this way. If this situation is common enough, and iterator_adaptor can be used to quickly generate iterators with the desired behavior (I haven't completely tested it as of yet, but it seems to work), then perhaps this is just one example of a reasonable "Hello, world" introduction to iterator_adaptors. Greg

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Regex matching quoted strings
by Poulson, Shawn 26 Jul '02

26 Jul '02

Hello all, I got Regex to compile and link into a project using MSVC6. My problem is in trying to implementing a command line parsing regexp that handles quoted strings. I have code that will selectively match quoted strings but somehow ignores non-quoted strings. The code fragment is below. I've read over Mastering Regular Expressions and some Perl Cookbook stuff but nothing works straight out of the book. Any tips? The code below finds all three parameters (in the spec var), but has no match for 'parm1'. Any help is certainly appreciated. Thanks. ----- 8< ----- 8< ----- boost::regex exp( "\"(?:(\\\\.|[^\"])*)\"[:space:]*" "|" "([^[:space:]]+)[:space:]*" ); std::string str = "parm1 \"parm2 parm3\" \"parm4 \\\"yo\\\"\""; std::string::const_iterator start = str.begin(), end = str.end(); boost::match_results<std::string::const_iterator> what; unsigned int flags = boost::match_default; while (boost::regex_search(start, end, what, exp, flags)) { std::string spec(what[0].first, what[0].second-what[0].first); std::string match(what[1].first, what[1].second-what[1].first); start = what[0].second; } ----- 8< ----- 8< ----- --- Shawn Poulson

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Re: [boost] Iterator Adaptor Poll
by Beman Dawes 26 Jul '02

26 Jul '02

At 04:46 PM 7/25/2002, David Abrahams wrote: >However, enough people have had problems approaching this library that I >thought it would be useful to ask about what would make a gentle >introductory example. Beman recently sent me the enclosed, but it seems to >define such an oddball toy iterator that I'm not sure it would be a very >good motivating example. ia_experiment.cpp is definitely oddball and definitely a toy. It was written to help me understand why I was getting compile errors from a real adaptor. Someone else can probably come up with an introductory example which is less oddball. But I'd like to defend the general principle of "toy" introductory examples. When someone knows nothing about a topic, a toy example is the best introduction. It is "known good", and can be used to verify that compilations using the library work as expected. It can be modified to see the effect of changes. Because it is a toy, it is totally non-threatening. It makes the reader feel superior, rather than like a dunce. The "C Programming Language" and "C++ Programming Language" books both started with a little "hello, world" program, very much a toy. Although simple, it starts the ball rolling with something that works and is understandable almost every reader. In the case of ia_experiment.cpp, it illustrates the relationship between the finished iterator, the Base class, and the Policies class with greater clarity IMO than documentation in any form other than C++ code. --Beman

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pass through buffer
by Tom Howard 26 Jul '02

26 Jul '02

Hi, I found some old emails about a pass through stream buffer, but I can't find it in the boost library. Am I going blind? Basically I'm in the middle of writing a gzstream class that compresses and decompresses data to and from a iostream and I thought this pass through buffer would be exactly what I need. Anyone know where it is or have any other pointers for me? Thanks in advance. Cheers, Tom Howard

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Fw: [boost] Iterator Adaptor Poll
by David Abrahams 25 Jul '02

25 Jul '02

Hi Everyone, Have you tried to use iterator adaptors and found the documentation wanting? I have recently updated the documentation in the CVS: http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/*checkout*/boost/boost/libs/ utility/iterator_adaptors.htm?rev=HEAD However, enough people have had problems approaching this library that I thought it would be useful to ask about what would make a gentle introductory example. Beman recently sent me the enclosed, but it seems to define such an oddball toy iterator that I'm not sure it would be a very good motivating example. I'm asking for input, especially from anyone who has "gotten over the hump" so to speak, with iterator adaptors. TIA, Dave --------------------------------- David Abrahams * Boost Consulting dave(a)boost-consulting.com * http://www.boost-consulting.com ----- Original Message ----- From: "Beman Dawes" <bdawes(a)acm.org> To: "Dave Abrahams" <david.abrahams(a)rcn.com> Cc: "Jeremy Siek" <jsiek(a)cs.indiana.edu> Sent: Thursday, July 25, 2002 3:21 PM Subject: Iterator adaptor example > Dave, > > Thanks for fixing the docs. I fixed and committed to CVS one more change > of BaseType -> Base. > > I found I needed an even more basic example than anything in the docs to > play with, particularly for creating an iterator from scratch, and put > together the attached. > > It is very simple, and does not demonstrate advanced features, but it > answered newbie questions I had in a way that only running code, modifying > it, and running again can do. (Not to mention fixing all the errors I made > before it would compile!) > > Feel free to include it in the distribution if you think it would help > others. Needs a better name of course. > > --Beman ---------- // Really dumb iterator_adaptor example program -----------------------------// // (C) Copyright Beman Dawes 2002. Permission to copy, use, modify, sell and // distribute this software is granted provided this copyright notice appears // in all copies. This software is provided "as is" without express or implied // warranty, and with no claim as to its suitability for any purpose. #include <boost/iterator_adaptors.hpp> #include <string> #include <iostream> class my_base { public: std::string name; my_base() : name( "foo" ) {} void operator++() { name = "bar"; } bool operator==( const my_base & rhs ) const { return name == rhs.name; } }; // if my_base had "const std::string & operator*() const { return name; }" // then custom policies would not be required. class my_policies : public boost::default_iterator_policies { public: template <class IteratorAdaptor> typename IteratorAdaptor::reference dereference(const IteratorAdaptor& x) const { return x.base().name; } }; typedef boost::iterator_adaptor< my_base, my_policies, // default_iterator_policies would do if my_base::op* were present const std::string, const std::string &, const std::string *, std::forward_iterator_tag, std::string::difference_type > my_iterator; int main() { my_iterator itr; my_iterator::value_type str( "hello, iterator\n" ); //verify value_type present std::cout << str; std::cout << *itr << std::endl; // foo std::cout << *++itr << std::endl; // bar std::cout << (itr == my_iterator() ? "bingo!" : "oops!" ) << std::endl; // oops std::cout << (itr == ++my_iterator() ? "bingo!" : "oops!" ) << std::endl; // bingo return 0; } [Non-text portions of this message have been removed]

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using boost::python v1
by Srivatsan Raghavan 25 Jul '02

25 Jul '02

hello all.. i've got some questions about using bpl, and i've searched the docs & the examples, and i can find no answer this example illustrates the issues i'm having <cpp> class B ; class C ; class A { public: A() ; virtual bool func1 ( ) ; virtual bool func2 ( ) = 0 ; virtual ~A() ; virtual int func3 ( std::list<C> ) ; protected : B m_Bobj ; std::string m_Aname ; } ; </cpp> now , i know how to expose the virtual and pure virtual functions to pyhon, i just write a derived class A_callback, and write some static default functions that forward the impl to the virtual function in A . my problem is in the func3() and the protected members do i need to write my own wrapper functions to python for mapping a list<C> ? or does bpl do this itself in some way? and how do i expose the protected members to python? if i do something like this : <cpp> boost::python::class_builder<A , A_callback> a_class ( this_module , "A" ) ; a_class.def ( &A::m_Bobj , "m_Bobj" ) ; </cpp> that line of code gets me this error (in msvc 6 : sp 5 ) : error C2248: 'm_Bobj': cannot access protected member declared in class 'Logging::Endpoint' <file-name> : see declaration of 'm_Bobj' how can i get this to work?

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Is bellman_ford_shortest_paths supposed to work for undirected graphs?
by Louis Lavery 25 Jul '02

25 Jul '02

int main() { enum {A,B,Z}; char const name[] = "ABZ"; int const numVertex = static_cast<int>(Z); typedef std::pair<int,int> Edge; Edge edge_array[] = {Edge(B,A)}; int const numEdges = sizeof(edge_array) / sizeof(Edge); int const weight[numEdges] = {11}; typedef adjacency_list<vecS,vecS,undirectedS,no_property,property<edge_weight_t,int> > Graph; Graph g(edge_array, edge_array + numEdges, numVertex); Graph::edge_iterator ei, ei_end; property_map<Graph,edge_weight_t>::type weight_pmap = get(edge_weight, g); int i = 0; for(tie(ei, ei_end) = edges(g); ei != ei_end; ++ei, ++i) { weight_pmap[*ei] = weight[i]; } std::vector<int> parent(numVertex); for(i = 0; i < numVertex; ++i) { parent[i] = i; } std::vector<int> distance(numVertex, std::numeric_limits<int>::max()); distance[A] = 0; // Set source distance to zero bool const r = bellman_ford_shortest_paths(g, int (numVertex), weight_map(weight_pmap).distance_map(&distance[0]). predecessor_map(&parent[0])); if (r) { for(int i = 0; i < numVertex; ++i) { std::cout << name[i] << ": " << std::setw(3) << distance[i] << " " << name[parent[i]] << std::endl; } } else { std::cout << "negative cycle" << std::endl; } return EXIT_SUCCESS; } Expected Output:- A: 0 A B: 11 A Actual Output:- A: 0 A B: 2147483647 B Louis.

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BGL: traversal algorithm for tree
by Björn Lindberg 25 Jul '02

25 Jul '02

I have implemented a rooted tree structure as a BGL graph. I need to be able to traverse the tree from root to leaves, while doing something at each vertex. I need to be able to do this as inorder and postorder traversal. My question is if it's possible to do this with any of the existing algorithms in BGL. My current thinking is to implement a function traversal( ... ), but if there already exists an alternative, I would prefer to use it. Björn

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