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[BGL] predecessor map from a view on a multi_array
by Geoff Hilton 04 Feb '10

04 Feb '10

Hi, I'm currently using MSVC9 and the code listed below doesn't compile, instead producing the following errors and warnings: Warning 1 warning C4100: 'x' : unreferenced formal parameter c:\program files\boost\boost_1_41_0\boost\concept\detail\msvc.hpp 20 test Warning 2 warning C4100: 'id' : unreferenced formal parameter c:\program files\boost\boost_1_41_0\boost\graph\dag_shortest_paths.hpp 86 test Error 3 error C2440: '<function-style-cast>' : cannot convert from 'int' to 'D' c:\program files\microsoft visual studio 9.0\vc\include\limits 109 test I know MSVC has issues with named parameters among other things, but I haven't been able to get it to compile with the non-named-parameters overload either, in this instance. What am I misusing and how am I misusing it? Also, I get the impression that the default combiner/comparer may be unsafe for floating-point comparisons and addition (with respect to over/underflow and comparing floating point values, I seem to recall it being a good idea never to compare with direct equalities, eg. x == infinity because of rounding issues). Might it be a good idea to further specialize appropriate areas of the algorithm code to account for this, or am I over-generalizing(specializing?)? How about a specialized closed_plus<> in relax.hpp which makes the comparisons more safely for floats and doubles (since both parameters "a" and "b" of closed_plus must be of type T anyway)? #include <boost/graph/adjacency_list.hpp> #include <boost/graph/dag_shortest_paths.hpp> #include <boost/multi_array.hpp> namespace geoff { typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::directedS ,boost::no_property, float> Graph; typedef boost::multi_array<boost::graph_traits<Graph>::vertex_descriptor, 2U> PredecessorsMatrix; typedef PredecessorsMatrix::array_view<1>::type PredecessorMap; } //namespace geoff int main(int /*argc*/, char* /*argv*/[]) { const std::size_t num_agents = 3; geoff::Graph graph; geoff::PredecessorsMatrix per_agent_matrix(boost::extents[num_agents][boost::num_vertices(graph)]); geoff::PredecessorsMatrix::index_gen indices; std::size_t agent_index = 0U; geoff::PredecessorMap agent_x_predecessors = per_agent_matrix[indices[agent_index][boost::multi_array_types::index_range()]]; boost::dag_shortest_paths(graph, 0, boost::predecessor_map(agent_x_predecessors)); } Thanks very much, Geoff

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[1.42] PDF documentation build available.
by John Maddock 04 Feb '10

04 Feb '10

Documentation for those Boost libraries that can have their documentation built as PDF is now available from the usual SF download page: https://sourceforge.net/projects/boost/files/ Individual links are: https://sourceforge.net/projects/boost/files/boost-docs/1.42.0/boost_pdf_1_… (26Mb) https://sourceforge.net/projects/boost/files/boost-docs/1.42.0/boost_pdf_1_… (25Mb) https://sourceforge.net/projects/boost/files/boost-docs/1.42.0/boost_pdf_1_… (24Mb) https://sourceforge.net/projects/boost/files/boost-docs/1.42.0/boost_pdf_1_… (23Mb) Enjoy! John.

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Re: [Boost-users] boost any questions and praise
by pete＠pcbartlett.com 04 Feb '10

04 Feb '10

[I fear this conversation is drifting off-topic, but I hope the moderators will forgive a further reply] > > and because it is an any he has no means of > > knowing for sure if the contents are streamable at instantiation time. > > Don't put an object into the any that can't be cout and then try and > cout the any. > > He has to "trust to luck". > > His code put the object into the any in the first place. No luck > involved. Or it's someone elses code but he knows what someone elses > code is giving. Ah you are lucky. You live in a world where you and your co-developers never make any mistakes and the documentation is always up-to-date. I am more fallible and make mistakes and if possible I'd prefer to be told about them via a compile-time error rather than blowing the stack at runtime. > There is more to an object than it's type. You can't just guess what > to give a function based on only the information that it wants one > unsigned integer. Sure - I don't think anyone has said type-safety is a panacea for all coding ills or a replacement for documentation. But the consensus is that it very helpful in C++. Incidentally, you may be interested in the Constrained Value library (http://student.agh.edu.pl/~kawulak/constrained_value/index.html) [1] So if your function needs something in [a,b] rather than [0,UINT_MAX] the type system can give some assistance. [snip irrelevant stuff about "lockup safe" - it's a non-sequitur ] > I do appreciate there are different views here, however if one has > chosen boost::any already then they already know what they want, > especially given the stuff in std. Suggesting that because you can > cause an error an error could unexpectedly occur when you pass > unknown objects into an unknown method in a non sensible example > that wouldn't happen isn't helpful. You have to appreciate where we are coming from. Your original post had code where you tried to pass the result of a runtime method as a template parameter. This suggests you are not hugely familiar with C++ and perhaps Boost.Any, so people naturally ponder whether Boost.Any really is the right choice (often it isn't) and try to help by making sure the OP has heard about the alternatives. > The documentation says that for boost::any a program doesn't crash > if you try and cast an any into a type it was not set as, it gives a > null instead. Actually, If try to retrieve a pointer to the type, it would return a null, if you tried to retrieve a value, it would throw bad_any_cast. > For crashing on stream insertion when it's contents can't be > inserted vs giving an error that will stop the program more safely > and tell the coder what went wrong, I think the latter is more > desirable, unless there is a significant performance difference in > which case either one is valid. Right, if you went down a has_operator_stream route, you could throw an exception instead of blowing the stack. Feel free to offer a patch along those lines if you want , but it opens up a can worms. If operator Links: ------ [1] http://student.agh.edu.pl/~kawulak/constrained_value/index.html)

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Problems with bind
by dilas dilas 04 Feb '10

04 Feb '10

If I have class with to versions of member function: const and non-const, and I use bind to access this member function, then I get a lot of errors. For example: struct A { void foo(void){}; void foo(void)const{}; }; const A a; lambda::bind(&A::foo,lambda::_1 )(a); Can I do something to solve this problem?

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IOStreams: Memory-Mapped files: persistency-question
by Florian Schwarz 04 Feb '10

04 Feb '10

Hello, I'm using the class mapped_file from boost/iostreams to read and write to a file. I stumbled across a persistency-question which I couldn't answer from the documentation. When I'm using a normal c++ ofstream, I can be sure that after I called flush(), that the data is written to disk, even if my program crashes afterwards. But what if I'm using a mapped_file, is there any way to ensure that the written data will reach the disc, even if my program crashes at some later point? Thanks a lot for your help in advance. Best regards Florian

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Re: [Boost-users] [StateChart] Inheriting state
by Tarcisio Fedrizzi 04 Feb '10

04 Feb '10

Hi, I had almost the same problem you have. I solved it in this way: #include <boost/statechart/state_machine.hpp> #include <boost/statechart/simple_state.hpp> #include <boost/statechart/event.hpp> #include <boost/statechart/custom_reaction.hpp> #include <boost/mpl/list.hpp> namespace sc = boost::statechart; namespace mpl = boost::mpl; struct Event1 : sc::event<Event1> {}; template<class Derived, class Outer> struct ActiveBase : sc::simple_state<Derived, Outer> { typedef sc::simple_state<Derived, Outer> base; sc::result react(const Event1& event) { return discard_event(); } using base::discard_event; }; struct Active; struct FSM : sc::state_machine<FSM, Active> { }; struct Active : ActiveBase<Active, FSM> { typedef sc::custom_reaction<Event1> reactions; }; int main() { FSM fsm; fsm.initiate(); } notice the custom_reaction instead on in_state reaction. If you see in the documentation the function to specify for the in state reaction must be: "...|| Either the state defining the in-state reaction itself or one of it direct or indirect contexts..." since the base state (ActiveBase) is not known to the library the library is not able to use the function specified in the in_state_reaction template. Indeed if you specify Active instead of BaseActive in the in_state_reaction template (like in_state_reaction<Event1, Active, &Active::f>) things work a bit better. However this failes to compile anyway because the third parameters is seen to be of type "void (ActiveBase<Active, FSM>::*)(const Event1&)" and this doesn't match the required type. Anyway this is only an hypothesis I would wait for the author response in order to have a correct response. Hope this is helpful. Bye, Tarcisio.

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Compile Boost with visual studio 2008 compiler for Windows CE 6.0
by Tim.Olmer＠priva.nl 04 Feb '10

04 Feb '10

Hi all, I am trying for a couple of days to compile Boost with the Visual Studio 2008 compiler for Windows CE 6.0 I want to use the Boost.Thread Library in Windows CE 6.0. I have understand that I first need to compile STLport. Can I use STLport out of the box or do I need a separate C library for windows CE ?? I have run the configure tool like this: C:\build\STLport-5.2.1>call configure evc9 -x --with-static-rtl --use-boost C:\boost\boost_1_41_0 cl.exe /nologo /TP /WX /GF /GR /EHsc /GL /MT /Zi /O2 /FC /D_STLP_USE_DYNAMIC_LIB /D_STLP_USE_DYNAMIC_LIB /D _WIN32_WCE=0x600 /D UNDER_CE=1 /D "UNICODE" /D "ARM" /D "_ARM_" /D "ARMV4I" /DNDEBUG /I "../../stlport" /I"C:\boost\boost_1_41_0" /c /Foobj\evc9-arm\shared\dll_main.o /Fd"obj\evc9-arm\shared\stlport_x.5.2.pdb" ../../src\dll_main.cpp dll_main.cpp c:\build\stlport-5.2.1\stlport\stl\_ctime.h(38) : error C2039: 'clock' : is not a member of '`global namespace'' c:\build\stlport-5.2.1\stlport\stl\_ctime.h(38) : error C2873: 'clock' : symbol cannot be used in a using-declaration c:\build\stlport-5.2.1\stlport\stl\_ctime.h(39) : error C2039: 'asctime' : is not a member of '`global namespace'' c:\build\stlport-5.2.1\stlport\stl\_ctime.h(39) : error C2873: 'asctime' : symbol cannot be used in a using-declaration c:\build\stlport-5.2.1\stlport\stl\_ctime.h(40) : error C2039: 'ctime' : is not a member of '`global namespace'' c:\build\stlport-5.2.1\stlport\stl\_ctime.h(40) : error C2873: 'ctime' : symbol cannot be used in a using-declaration c:\build\stlport-5.2.1\stlport\stl\_ctime.h(41) : error C2039: 'gmtime' : is not a member of '`global namespace'' c:\build\stlport-5.2.1\stlport\stl\_ctime.h(41) : error C2873: 'gmtime' : symbol cannot be used in a using-declaration c:\build\stlport-5.2.1\stlport\stl\_ctime.h(46) : error C2039: 'mktime' : is not a member of '`global namespace'' c:\build\stlport-5.2.1\stlport\stl\_ctime.h(46) : error C2873: 'mktime' : symbol cannot be used in a using-declaration c:\build\stlport-5.2.1\stlport\stl\_ctime.h(47) : error C2039: 'localtime' : is not a member of '`global namespace'' c:\build\stlport-5.2.1\stlport\stl\_ctime.h(47) : error C2873: 'localtime' : symbol cannot be used in a using-declaration c:\build\stlport-5.2.1\stlport\stl\_ctime.h(48) : error C2039: 'strftime' : is not a member of '`global namespace'' c:\build\stlport-5.2.1\stlport\stl\_ctime.h(48) : error C2873: 'strftime' : symbol cannot be used in a using-declaration c:\build\stlport-5.2.1\stlport\stl\_ctime.h(49) : error C2039: 'time' : is not a member of '`global namespace'' c:\build\stlport-5.2.1\stlport\stl\_ctime.h(49) : error C2873: 'time' : symbol cannot be used in a using-declaration Does anyone know why I get this error and how to solve this? Thanks in advance! ______________________________________________________________________ Priva B.V. A disclaimer is applicable to this email, please refer to www.priva.nl/disclaimer. Op deze email is een disclaimer van toepassing, ga naar www.priva.nl/disclaimer.

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How to convert wide character strings to multi-byte strings ?
by Timothy Madden 04 Feb '10

04 Feb '10

Hello What is the right way to convert from wide character strings to multi-byte strings ? In boost or in C++ if any ? For narrow to wide conversion I can do wostringstream streamMsg; streamMsg << "Narrow string"; wstring wstrMessage = streamMsg.str(); But I think that too is not a good way as it might not take the current locale / code page /encoding /whatever into account, but just widen the char (as a number) to an wchar_t. So what is the right way ? How do I write a codecvt facet for the default locale if I need one ? Thank you, Timothy Madden

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array of small world graphs
by Vasilis Hatzopoulos 04 Feb '10

04 Feb '10

Hi all, new to boost and experiencing a bit of an issue with generating a collection of small worlds. Basically i want for each pass of the loop to generate a small world with a certain pRewire. Here's some code typedef small_world_iterator<mt19937, Graph> SWGen; base_generator_type generator(1u); for(int i = 0; i < num_graphs; i++){ Graph g( SWGen( generator, N, k, pRewire, SWGen(), N ); . . some operations on g, i.e. path lengths e.t.c. } As it happens all graphs g are the same graph while what i want is a collection of different small worlds with the same pRewire. Why does the state of the generator not advance after the first Graph is generated? Can anyone please help me with this. Thanks for your time, Vasilis.

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building boost under mingw-w64
by Alexander Kalinin 04 Feb '10

04 Feb '10

Hi, Here some details about building boost under mingw-w64. I am using only "threads" and "date_time" libraries from boost and I started to building boost by command: bjam --prefix=c:\boost toolset=gcc address-model=64 variant=debug,release link=static,shared threading=multi --with-thread --with-date_time install and I got an error: ./boost/thread/win32/basic_ timed_mutex.hpp:152: error: cast from 'void*' to 'long int' loses precision This caused by the macros BOOST_INTERLOCKED_COMPARE_EXCHANGE_POINTER defined in interlocked.hpp. This macros has several definitions that depends on building defines. So I add BOOST_USE_WINDOWS_H define into the building command: bjam --prefix=c:\boost toolset=gcc address-model=64 variant=debug,release link=static,shared threading=multi --with-thread --with-date_time define=BOOST_USE_WINDOWS_H install add boost was compiled successful. The question is. Is it possible to build boost under mingw-w64 without BOOST_USE_WINDOWS_H define?

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