September 2011 - Boost-users - lists.preview.boost.org

from a variant to class with members templated over the variant types
by Olivier Tournaire 21 Sep '11

21 Sep '11

Hi all, I am not sure if the title is self explanatory, so, let me show an example of the goal. I have: variant<type1, type2, type3> v; I want: struct { anobject<type1> _type1_object; anobject<type2> _type2_object; anobject<type3> _type3_object; } Is there a way to do such a thing with boost pp (or something else)? Regards, Olivier

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Re: [Boost-users] [Timer] Using progress timers
by Alex Perry 21 Sep '11

21 Sep '11

On Wed, 21 Sep 2011 11:47:35 +0100 Robert Jones wrote:- > cat progress.cpp > > #include <boost/progress.hpp> > > int main( ) > { > boost::progress_timer t; > > sleep( 5 ); > > return 0; > } > > > g++ progress.cpp > > > ./a.out > 0.00 s > > I was expecting a number >= 5.00 s! What am I missing? Not sure if its any help but above does work on windows with appropriate change to sleep >type test.cpp #include <boost/progress.hpp> #include <windows.h> int main( ) { boost::progress_timer t; Sleep( 5000 ); return 0; } >cl test.cpp Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.30319.01 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. test.cpp Microsoft (R) Incremental Linker Version 10.00.30319.01 Copyright (C) Microsoft Corporation. All rights reserved. /out:test.exe test.obj C:\workspace\Test>test 5.00 s HTH Alex

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[UTF] documentation of runtime configuration programmatically
by gast128 20 Sep '11

20 Sep '11

Hello all, the documentation of Boost.Test contains the following sentence "The UTF provides two ways to set a parameter at runtime: by specifying a command line argument and by setting an environment variable. The command line argument always overrides the corresponding environment variable." However it does not explain how. For example if I add this line to my code it crashes: boost::runtime::env::get<bool>("BOOST_TEST_AUTO_START_DBG"); Anyone?

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[Serialization]Serialization of nested stl object
by Kangkook Jee 20 Sep '11

20 Sep '11

Hi, all A member of a target class, where one STL object (map) includes another (set), prevent the code from being built properly and the error message urges me to implement *serialize* method for pair<string*, set<unsigned>>. What is the typical way of implementing serialization using boost for this kind of data structures? * Code snippet class B { … map<const string*, set<unsigned> > lines; .. template<class Archive> void serialize (Archive & ar, const unsigned int version) { ar & lines; … * Build error message /opt/local/include/boost/serialization/access.hpp:118: error: ‘class std::map<const std::string*, std::set<unsigned int, std::less<unsigned int>, std::allocator<unsigned int> >, std::less<const std::string*>, std::allocator<std::pair<const std::string* const, std::set<unsigned int, std::less<unsigned int>, std::allocator<unsigned int> > > > >’ has no member named ‘serialize’ Thanks for your help in advance, /Kangkook

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shared_ptr design question
by John M. Dlugosz 20 Sep '11

20 Sep '11

I'm wondering why there is not an efficient built-in way to check whether two things (e.g. a shared_ptr and a weak_ptr, but any combination should work) refer to the same object. In my implementation, I found that a handy thing to have. In changing code that uses a different home-brew smart pointer, I have to achieve this. The only way I see is to first resolve the weak pointer, and then compare the get() from each. That needlessly yoyo's the reference count, which is a horribly expensive atomic operation. I find that in the new C++ standard it refers to a owner_before ordering function, which is a bit more obscure than just comparing the pointers. So I'm wondering why this is not provided. Is there some reason why the feature is obscured, for portability? —John

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gdb pretty printers
by Jonathan Brannan 20 Sep '11

20 Sep '11

Are there any pretty printers for the more complex boost types? Specifically I'm looking for boost::multi_index printers as looking at in debug seems unhelpful.

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Flow rate dimensional analysis
by Michael Powell 19 Sep '11

19 Sep '11

Boost::units users, I am trying to perform a flow rate through an orifice calculation (Volume per Time or L^3T^-1) using the following dimensional analysis: Q = Cf * A * sqrt( 2 * abs(P1-P2) ) On paper the dimensional analysis works out correctly. I know we should be receiving a L^3T^-1 consequent to the calculation. If I just take this on one line, it seems to compile: __C_flow * __a_orifice * boost::units::sqrt(__two * __p_diff / __d); Where __a_orifice is the area of the orifice, __p_diff is the pressure differential (absolute value), and __d is the mass density. __C_flow (coefficient of flow through orifice) and __two (2.0) are both dimensionless. In terms of units quantities, these are all defined as quantity<si::area>, quantity<si::pressure>, quantity<si::mass_density>, and quantity<si::dimensionless>, to start with. I think my flow-rate dimension and/or unit must be incorrect, but I am failing to see why in order to know what to do to correct the error. typedef boost::units::derived_dimension<boost::units::length_base_dimension,3 ,boost::units::time_base_dimension,-1>::type flow_rate_dimension; typedef boost::units::unit<cs::units::flow_rate_dimension,boost::units::si::system> flow_rate; When I take: si::flow_rate __fr = __C_flow * __a_orifice * boost::units::sqrt(__two * __p_diff / __d); I am receiving the following compiler error as my clue... Error 1 error C2440: 'initializing' : cannot convert from 'boost::units::quantity<Unit,Y>' to 'boost::units::quantity<Unit,Y>' c:\Source\Simulations\CS.Calculations.Managed\Calculators\Calculator.cpp 461 CS.Calculations.Managed I'd like to set this up in as base a dimension as possible because later on we'll be introducing unit views, converting from base units to a view unit, or unit system, along these lines, but if we have to specify this in specific unit terms, so be it. We'll worry about unit conversions later on. Best regards, Michael Powell

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How do you handle state-independent events efficiently in MSM?
by Peter Gissel 19 Sep '11

19 Sep '11

I have a state machine that has a large number of event types but only a few different states. Some of the events can be received regardless of the state and the same action is taken regardless of which state the machine is in, so the event is really unrelated to the state. I there an efficient way of handling the events that are state independent rather than defining a transition from every possible state for each state independent event? A number of the events do transition the state machine and depend on the current state, so a transition is necessary. But if no state change is required for the event and the current state is not important, I'm not sure how to define event handling without defining a transition from all possible states. This winds up creating a much larger number of transitions than I really need, and a much longer compile time than I would like. I am looking for some way to handle these states that would still give me good run time speed, put not pay the penalty that defining a large number of transitions would impose. Thanks! Peter Gissel

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threads: shared lock question
by Mark Higgins 19 Sep '11

19 Sep '11

I'm new to threads and boost, so I'm sure this is a real newbie question and hopefully quite easy to answer! I'm trying to set up a pool of threads that do a calculation, and I want to wait for those calculations to finish. Normally I'd do thread_group.join_all() to wait for the threads to exit - but in this case I want my threads hanging around so that I can redo that calculation over and over again when I ask it to do. What's the best way to signal back to the main thread that all calculations are complete? Should I use a barrier?

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What concepts/interface must the element type of multi_index_container<> support?
by Chris Cleeland 19 Sep '11

19 Sep '11

I'm trying to use boost::multi_index_container on a type that I've defined. I want the container to have two indices: 1. insertion order 2. hashed_unique Further, I want the hash to use an sha1 hash value, which I have represented as a struct. So, I have something like the following: struct sha1_hash_value { ... }; class MyRecord { public: ... sha1_hash_value hash() const { return _sha1_hash; } ... private: sha1_hash_value _sha1_hash; }; using namespace boost::multi_index; typedef boost::multi_index_container< MyRecord, indexed_by< sequenced<>, hashed_unique<const_mem_fun<MyRecord,sha1_hash_value,&MyRecord::hash> > > > RecordSet; When I compile this, I get lots of complaints regarding the conversions to/from the 'sha1_hash_value' type. I understand that I need to define appropriate member functions or specializations for this type. What I would like to know is what those member functions/specializations are and where that is documented so that I don't have to decipher compiler error gibberish iteratively and just cross my fingers that the errors are really about missing functionality and not about misuse. FWIW, if I change sha1_hash_value to a 'long', the code compiles, so it doesn't appear as if I'm completely misusing multi_index_container<>, though I'm certainly still open to that possibility as well. Thanks for any help. The brick wall I'm banging my head against is really starting to hurt.

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