May 2005 - Boost-users - lists.boost.org

dijkstra_visitor
by Andreas Fabri 02 May '05

02 May '05

Hello, I wrote my own dijksta visitor for the shortest path algorithm, and on an event I wanted it to write something in a bundled property of a vertex. However this didn't compile because the graph is a const&. Is there a way to solve this problem? Thanks in advance, andreas

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[conversion] RoundEven odd behaviour
by Vyacheslav E. Andrejev 02 May '05

02 May '05

Hello All I tried to use boost numeric conversion library and faced with strange feature of RoundEven that I can not comprehend or find expanation in the documentation. First I thought that this policy rounds float number to nearest integer, because RoundEven::round_style::value == std::round_to_nearest. But! This policy for example returns 2.0 for 3.0 as argument! cout << boost::numeric::converter< int , double , boost::numeric::conversion_traits<int, double> , boost::numeric::silent_overflow_handler , boost::numeric::RoundEven<double> >::convert(2.9) << endl; cout << boost::numeric::converter< int , double , boost::numeric::conversion_traits<int, double> , boost::numeric::silent_overflow_handler , boost::numeric::RoundEven<double> >::convert(3.0) << endl; cout << boost::numeric::converter< int , double , boost::numeric::conversion_traits<int, double> , boost::numeric::silent_overflow_handler , boost::numeric::RoundEven<double> >::convert(3.1) << endl; Output of the program above will be: 3 2 3 What is the cause of such strange behaviour? This is a bug or there is something that I don't understand? -- Vyacheslav E. Andrejev System Architect, Excelsior, LLC

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How to get type given pointer to base?
by Delfin Rojas 02 May '05

02 May '05

Hello all, I hope somebody can help me with this. What I want to do is the following: Let's say I have a templated class called Foo template<class U> class Foo { public: Foo(U * p) : m_p(p) {} ~Foo() {} U* getP() const { return m_p; } private: U* m_p; }; Now let's say I want to have a collection of pointers to Foo. What should I do? The possibilities I can think of are the following: 1) Create a class FooBase and have Foo inherit from FooBase. FooBase is non-templated so there should be no problem with having a collection of pointers to FooBase where I can put instances of Foo. The problem with this approach is that given a FooBase* in that collection I could not use the getP method because I would not know what type of Foo it holds. 2) Create a boost::variant of all the possible types of Foo<U>* I want to have. Then have a collection of this FooVariant. Using static visitation I can obtain the original type of Foo<U>* in a given FooVariant. The problem with this approach is that I get an ICE from VC++ 7.1 when the type of U gets too complex (shared_ptr to another type for example). Have I overlooked something? Is there a better technique for what I want to achieve? Any help would be great, Thanks Delfin Rojas

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searching boost::teebuf : public std::streambuf
by Elmar Loos 01 May '05

01 May '05

Hello, in the archive of this mailinglist I found some Mails from year 2000, that a teebuf derived from std::streambuf should be inserted into boost. I couldn't find anything like this in the current boost version. Could you tell me something about the status of that class, please? Bye Elmar

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