January 2013 - Boost-users - lists.boost.org

Re: [Boost-users] [MultiIndex] more on key extractor issues
by John M. Dlugosz 21 Jan '13

21 Jan '13

On 1/20/2013 11:00 AM, boost-users-request-at-lists.boost.org |Boost/Allow to home| wrote: > From: Joaquin M Lopez Munoz<joaquin(a)tid.es> > Thanks for your elucidation. I'm much more comfortable with the class now. Like most people in this situation, having found the explanation I'm much to busy trying to employ it in real-world projects and don't have time to edit and expand the docs. But, a pointer to your responses on an archiver might be a great quick addition to the documentation page. It occures to me that if the docs were a Wiki then more might get done, including fixing typos and putting this kind of commentary on the Discussion page. —John

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[MSM] Get state name as string
by Stefan Wiehler 20 Jan '13

20 Jan '13

Hello, For debugging purposes, I want to get the current state name as a string. For this purpose I found the class get_state_name in the tools section of the backend. Unfortunately there is no example on how to use this method in the documentation nor anywhere else; and the extensive use of templates makes it very difficult for me to infer this. I am especially confused about the argument boost::msm::wrap<StateType> const& of the call operator. What do I have to provide her? Could anybody please post a short example how to this? Kind regards, Stefan Wiehler

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Re: [Boost-users] [MultiIndex] more on key extractor issues
by John M. Dlugosz 20 Jan '13

20 Jan '13

> Have you taken a look at the table in: > > http://www.boost.org/libs/multi_index/doc/tutorial/ > key_extraction.html#advanced_key_extractors > > Regardless of whether the indexed-by member is const or not, when using > pointers to const elements the proper way of declaring the extractors is: > > > member< > ItemBase, > const unsigned long, > &ItemBase::some_member > > > > member< > ItemBase, > const S2, > &ItemBase::another_member > > > > This should clear problems away both in VS and Clang (please report > otherwise.) > > Joaqu?n M L?pez Mu?oz > Telef?nica Digital > > I read that part in detail (including the typo, T:gg instead of T::gg), going over all the MI docs again after my postings. I agree this seems to address that use-case, but I really don't understand the table and section, and certainly had no clue what it was getting at when I read it without this issue specifically in mind. "The column "applicable to |const| elements?" states whether the corresponding key extractor can be used when passed constant elements (this relates to the elements specified in the first column, not the referenced |T| objects)." What does that mean? I was actually looking at this in regards to figuring out what a non-const member function extractor was good for. "this also implies that |multi_index_container|s of elements of |T| cannot be sorted by |T::g| or |T::gg|," if you are not using it to sort by, what is the point of having the key extractor? Anyway, I found that it works correctly on both compilers if the middle argument (the key type) is declared const for member and not for const_mem_fun. I suppose that is due to differences in the metaprogramming, but really they should be treated the same. Const on the first parameter, T, doesn't seem to matter if it's declared const or not. ---John

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Re: [Boost-users] [MultiIndex] is ordered_non_unique stable?
by John M. Dlugosz 20 Jan '13

20 Jan '13

> The only problem with this is that the behavior is *undocmented*. If you want > to stay legal, use hinted insertion with end() (which will *documentedly* > work for all the ordered_non_unique indices of your container, not only the one > you happen to be doing for the insertion.) > > Joaqu?n M L?pez Mu?oz > Telef?nica Digital > > > That is very interesting. The wording is kind of strange though: "If succesful, insertion happens as close as possible to the location just prior to |position|." I wonder if stability was the intention? Thank you very much for your analysis of the code. ---John

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Help a novice today getting started with regex.hpp
by Neil Sutton 20 Jan '13

20 Jan '13

Please can someone tell me the best place to start studying how to write and use boost::regex.hpp? Is there any documentation or tutorial that is easier for a novice to understand than the standard distribution documentation?

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[Container] --begin() on empty deque crashes
by TONGARI 20 Jan '13

20 Jan '13

Hi there, The code below would simply crash on g++ 4.7.1/MinGW with default optimization level, it doesn't shown with -O/1/2/3 ---------------------------------------- boost::container::deque<int> d; --d.begin(); ---------------------------------------- I took a look into the impl, seems that it dereferences from (this->m_node - 1) which is invalid at the time. I guess it's the problem. Thoughts?

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[asio] How do you fake the time for boost timers?
by Josh Quigley 20 Jan '13

20 Jan '13

(For those interested this question is also at http://stackoverflow.com/questions/14191855/how-do-you-fake-the-time-for-bo… ) Hi all, If possible, how do you fake the time for the purpose of triggering boost timers in a unit test? For example, is it possible to achieve something like the following: #include <iostream>#include <boost/asio.hpp>#include <boost/date_time/posix_time/posix_time.hpp> void print(const boost::system::error_code& /*e*/){ std::cout << "Hello, world!\n";} int main(){ boost::asio::io_service io; // Possibly another class needed here, or a way of setting the clock to be fake boost::asio::deadline_timer t(io, boost::posix_time::hours(24)); t.async_wait(&print); io.poll(); // Nothing should happen - no handlers ready // PSEUDO-CODE below of what I'd like to happen, jump ahead 24 hours io.set_time(io.get_time() + boost::posix_time::hours(24)); io.poll(); // The timer should go off return 0;} I'm aware I could wrap the io_service and deadline_timer in a wrapper and write my own test implementation, thus providing the real and test version to the production code I'm trying to test. What I'm hoping is the boost framework allows a way to create an io service that is related to a fake clock rather than the system time, meaning I don't need to create my own wrappers. I should also point out that the docs indicate providing something like my own WaitableTimerService orTimerService may be the way to go, but I can't see which one (if any) is responsible for providing the clock. Any tips appreciated! Josh.

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[MultiIndex] more on key extractor issues
by John M. Dlugosz 19 Jan '13

19 Jan '13

I think my problem stems from the use of 'const' in the underlying element with pointer traversal. Consider: typedef multi_index_container< shared_ptr< const ItemBase >, indexed_by< ordered_non_unique< member< const ItemBase, // <<--- here const unsigned long, // <<--- here &ItemBase::some_member > >, // ordered_non_unique ordered_unique< tag<S2>, member< ItemBase, const S2, &ItemBase::another_member > > // ordered_unique > // indexed_by > ItemList_type_base; I added the two 'const' occurrences on the lines marked with "here", and it behaved better. I think it worked with the second index originally because one of those const's was originally there. The member in question was originally const, so I had included const as part of the type there. Basically, what is happening on Windows VS10 is: template<class Class,typename Type,Type Class::*PtrToMember> struct non_const_member_base { typedef Type result_type; template<typename ChainedPtr> #if !defined(BOOST_NO_SFINAE) typename disable_if< is_convertible<const ChainedPtr&,const Class&>,Type&>::type #else Type& #endif operator()(const ChainedPtr& x)const { return operator()(*x); // <<-- HERE } const Type& operator()(const Class& x,int=0)const { return x.*PtrToMember; } Type& operator()(Class& x)const { return x.*PtrToMember; } }; The ChainedPointer form unpeels a const-qualified type with (*x), and that matches the middle form, not the third. But the signature on the first form is looking for Type, which is exactly what I put in the member<...> index directive. So, I suggest that a quick note concerning constant types inside chained pointer following could be added to the tutorial section. Meanwhile, a stranger problem occured on the Mac, using the Clang compiler. I got an error saying that none of the operator() candidates were viable for overloading, with the error indicating that the type of thing being passed in was the shared_ptr<const ItemBase>. It said the first form was ignored because of instantiation failure, but that is exactly contrary to the disable_if. I'm suspecting that the is_convertable itself somehow choked rather than producing false_type...? Naturally none of the other overloads matched, as a shared_ptr<T> cannot be passed where a T is expected, and that's exactly when the first form would be switched in! —John

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[MultiIndex] is ordered_non_unique stable?
by John M. Dlugosz 19 Jan '13

19 Jan '13

Will equivalent elements in a ordered_non_unique index be "stable" and maintain their relative ordering based on the order in which they were inserted? Or do I need to use a complex key, adding my own sequence number, to ensure the desired ordering? —John

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Re: [Boost-users] [serialization] Serializing derived
by Brown, Matt 18 Jan '13

18 Jan '13

Hi Daniel, You may have already considered this option, but what if you were to require a template argument for which the user could pass a serialization behavior class ... much like an allocator for STL containers. I.E. YOUR CODE: template <typename T, typename serialize_T> struct container { void serialize(unsigned version) {serialize_T::do(data, version);} virtual ~container() = default; T data; }; USER'S CODE: struct my_serialize { static void do(SOME_TYPE data, unsigned version) {<user does what's needed here>} }; typedef container<SOME_TYPE, my_serialize> my_container; Maybe of some help to you? -- Matt ________________________________ This e-mail contains privileged and confidential information intended for the use of the addressees named above. If you are not the intended recipient of this e-mail, you are hereby notified that you must not disseminate, copy or take any action in respect of any information contained in it. If you have received this e-mail in error, please notify the sender immediately by e-mail and immediately destroy this e-mail and its attachments.

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