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[OT] Boost Programming forum
by Daniele Barzotti 30 Nov '13

30 Nov '13

Hi, I'm sorry for this off-topic but... I received an email which informs me that I was been registered into this forum: http://www.boostprogramming.com/forum/index.php So, since I'm not register myself, I would ask if this site has some relation with boost community. Regards, Daniele.

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[Multi-Index] Skip-Scan "virtual" ordered-non-unique index on top of composite ordered-unique index
by Dominique Devienne 29 Nov '13

29 Nov '13

We have BMIs of entries with complex composite "natural-keys". For example: typedef boost::multi_index_container< FooIdPtr, // FYI: boost::shared_ptr<FooId> bmi::indexed_by< EntityIndex<ByUid>::unique, // FYI: Surrogate/Primary Key EntityIndex<ByNKey>::of<FooId>::unique, // FYI: Natural Key // additional indexes by type, name and parent EntityIndex<ByType>::non_unique, EntityIndex<ByName>::non_unique, EntityIndex<ByParent>::non_unique > > Impl; The EntityIndex template utility simply factors the index definitions used in several BMIs. For example template <> struct EntityIndex<ByNKey> { template <typename T_IDENT> struct of { typedef hashed_unique< // natural key (logical primary key) tag<ByNKey>, identity< shared_ptr<T_IDENT> >, EntityIdHash<T_IDENT>, EntityIdPred<T_IDENT> > unique; }; }; template <> struct EntityIndex<ByParent> { typedef hashed_non_unique< tag<ByParent>, BOOST_MULTI_INDEX_CONST_MEM_FUN( EntityId, const Uid&, parent_uid // FYI: EntityId is the base class of FooId and co. ) > non_unique; }; After recently reading http://www.sqlite.org/draft/optoverview.html#skipscan and its Skip-Scan optimization, I wondered about changing my ByNKey unique index from hashed to ordered, and thought that in theory, I could perhaps avoid the maintenance and memory cost of the additional type+name+parent indexes, since all three are subsets of the ByNKey unique index, and using a similar skip-scan strategy, which might/would still provide reasonable performance, at least better than no index at all (i.e. a full scan). I know BMI does not provide this of course, but do you think Joaquin that it would be possible to one-day add such "virtual" ordered non-unique indexes on top of an existing ordered (possibly unique) composite index? Of course in this case, the composite'ness is hidden inside FooId, and not exposed to BMI (it used to be a true BMI composite index, but modeling the identity as an object made more sense and simplified things), so whether an index is a subset of another would need to be "configurable" in some way, to yield a "compatible key" with the right "prefix" keys to skip to the next "sub-range" to scan (hopefully that makes sense...). I think I would be able to write custom code on top of a ByNKey ordered-non-unique index to implement a subset of the functionality a true BMI ordered non-unique index provides, for my own needs (with some difficulty, but feasible nonetheless), but the kind of template meta-programming BMI uses to implements its indexes is beyond my current skill level, which is why I'm posting to see what the experts (i.e. Joaquin) thinks about this Skip-Scan virtual indexes idea. Thanks, --DD

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Serialization problem with cyclic references (pointers)
by krisdamato 29 Nov '13

29 Nov '13

Try steppin through this code where the deserialization takes place. On every machine I've tried this (and I've tried it with two different Boost builds as well) parent stays null every time. Can anyone point out the reason why? This is giving me a headache :( I suspect it's got something to do with there being cyclic references between parent and child... #include <boost\archive\binary_oarchive.hpp> #include <boost\archive\binary_iarchive.hpp> #include <boost\serialization\vector.hpp> #include <fstream> #include <memory> #include <vector> class A { public: A() { parent = nullptr; someInt = 0; } template <class Archive> void serialize(Archive& archive, const unsigned int version) { archive & someInt; archive & parent; archive & children; } int someInt; A* parent; std::vector<A*> children; }; int main() { A* newA = new A(); A* newPtr = new A(); newPtr->someInt = 5; newPtr->parent = newA; newA->children.push_back(newPtr); // Save. std::ofstream outputFile("test", std::fstream::out | std::fstream::binary); if (outputFile.is_open()) { boost::archive::binary_oarchive outputArchive(outputFile); // Serialize objects. outputArchive << newA; outputArchive << newPtr; outputFile.close(); } delete newA; delete newPtr; newA = nullptr; newPtr = nullptr; // Load.| std::ifstream inputFile("test", std::fstream::binary | std::fstream::in); if (inputFile && inputFile.good() && inputFile.is_open()) { boost::archive::binary_iarchive inputArchive(inputFile); // Load objects. inputArchive >> newA; inputArchive >> newPtr; inputFile.close(); } return 0; } -- View this message in context: http://boost.2283326.n4.nabble.com/Serialization-problem-with-cyclic-refere… Sent from the Boost - Users mailing list archive at Nabble.com.

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[Exception] How do I inherit custom exception hierarchy from std::runtime_error rather than from std::exception?
by Egor Tensin 29 Nov '13

29 Nov '13

Hi, The issue that's confusing me arose from my intention of inheriting my exception classes from std::runtime_error rather than from std::exception. It seemed logical to me, as my exceptions are really runtime errors; getting something meaningful via what() also seemed like a good idea. However, this doesn't compile: #include <iostream> #include <stdexcept> #include <boost/exception/all.hpp> typedef boost::error_info<struct tag_foo_info, unsigned long> foo_info; struct foo_error : virtual boost::exception, virtual std::runtime_error { explicit foo_error(const char *const what) : std::runtime_error(what) { } explicit foo_error(const std::string& what) : std::runtime_error(what) { } }; static void foo() { BOOST_THROW_EXCEPTION(foo_error("foo error") << foo_info(42)); } int main(int argc, char *argv[]) { try { foo(); } catch (const std::exception& e) { std::cerr << boost::diagnostic_information(e); return 1; } return 0; } It says that there's no default constructor available for std::runtime_error. How do I fix this or should I use the idiomatic approach? The interesting thing is that if I erase the "virtual" keyword, the program compiles flawlessly. I wonder what is the reason for that, e.g. why the original code doesn't work and why the new code does, what are the consequences of making boost::exception and std::runtime_error base (non-virtual) classes, etc. I'm confused as the docs clearly recommends I build exception classes hierarchy using virtual inheritance. Could somebody please give me an insight into the inner workings of the library & inheritance mechanisms? Thank you in advance, Egor.

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[Bind & Function] c function pointers
by Matthijs Möhlmann 29 Nov '13

29 Nov '13

Hello all, It was pointed out to me that the subject line was not correct, so I resent this mail with a correct subject line. I'm not sure if this is possible at all, but let me explain: I have the following function signature: typedef int (*sasl_callback_ft)(void); That function in question gets called with unknown amount of parameters (usually 3 or 4) Now I want to assign a member function to it: class admin { public: int callback_fun(void *context, int id, const char **result, unsigned *len); } boost::function<int(void *, int, const char **, unsigned *)> callback = boost::bind(&admin::callback_fun, this, _1, _2, _3, _4); Obviously the compiler doesn't allow to assign callback to a sasl_callback_ft var sasl_callback_ft fun = callback; I get compiler errors like: matthijs@hammer:~/t2$ clang++ -o main -std=c++11 main.cpp main.cpp:22:19: error: no viable conversion from 'boost::function<int (void *, int, const char **, unsigned int *)>' to 'sasl_callback_ft' (aka 'int (*)()') sasl_callback_ft cbfun = cb; ^ ~~ /usr/include/boost/function/function_template.hpp:894:5: note: candidate function operator safe_bool () const ^ 1 error generated. Attached the testcase I made for this. Regards, Matthijs

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Re: [Boost-users] [Thread] Using thread accross libraries
by Sébastien Gallou 29 Nov '13

29 Nov '13

Antony, Thanks a lot for your answer. But I check the configuration of each project, and same runtime-library is used (/MDd) in both cases. So my problem doesn't come from here. If you have another idea... Thanks for your help, Sébastien

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[Multi-Index] performance difference between lower_bound() and upper_bound()
by Dominique Devienne 29 Nov '13

29 Nov '13

I have a multi-index BMI (Boost 1.44), with an ordered_non_unique index on a"name" string field, which is lexicographically ordered. I'm searching for the range of values of the form "$prefix $integer", i.e. "foo 1", "foo 99", etc... to obtain this "range", I initially used (pseudo-code): auto begin = by_name_index().lower_bound(prefix + " 0"); auto end = by_name_index().upper_bound(prefix + " 9"); and within the range I test the suffix for its number'ness and keep the largest number. But I was surprised to see it performed badly for large number of calls. I switched to using instead: auto begin = by_name_index().lower_bound(prefix + " 0"); auto end = by_name_index().lower_bound(prefix + " :"); And this performs much better (20x). The "corpus" of names of this particular test may be skewing the results, since entries are added to the BMI with monotonically increasing number suffixes, and all entries have the prefix I'm looking for, yet I'm very surprised of such a large performance difference between the lower/upper version, and the lower/lower version. Anyone has a clue what could be going on? Thanks, --DD PS: I'm assuming the two versions are equivalent. Let me know if I'm mistaken please. This is not yet thoroughly tested.

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Put the Library Name in the Subject Line (was: boost and c function pointers)
by Mateusz Loskot 29 Nov '13

29 Nov '13

On 29 November 2013 09:29, Matthijs Möhlmann <matthijs(a)cacholong.nl> wrote: > boost::function<int(void *, int, const char **, unsigned *)> callback = > boost::bind(&admin::callback_fun, this, _1, _2, _3, _4); Please, Put the Library Name in the Subject Line [1], it will save people's time. Name Boost refers to a *collection of libraries, hence Boost has nothing to do with C function pointers. [1] http://www.boost.org/community/policy.html#subject-line Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

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boost and c function pointers
by Matthijs Möhlmann 29 Nov '13

29 Nov '13

Hello all, I'm not sure if this is possible at all, but let me explain: I have the following function signature: typedef int (*sasl_callback_ft)(void); That function in question gets called with unknown amount of parameters (usually 3 or 4) Now I want to assign a member function to it: class admin { public: int callback_fun(void *context, int id, const char **result, unsigned *len); } boost::function<int(void *, int, const char **, unsigned *)> callback = boost::bind(&admin::callback_fun, this, _1, _2, _3, _4); Obviously the compiler doesn't allow to assign callback to a sasl_callback_ft var sasl_callback_ft fun = callback; I get compiler errors like: matthijs@hammer:~/t2$ clang++ -o main -std=c++11 main.cpp main.cpp:22:19: error: no viable conversion from 'boost::function<int (void *, int, const char **, unsigned int *)>' to 'sasl_callback_ft' (aka 'int (*)()') sasl_callback_ft cbfun = cb; ^ ~~ /usr/include/boost/function/function_template.hpp:894:5: note: candidate function operator safe_bool () const ^ 1 error generated. Attached the testcase I made for this. Regards, Matthijs

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[mpl][fusion] How to transform vector_c into std::vector?
by Mostafa 29 Nov '13

29 Nov '13

How does one transform an mpl:vector_c into a regular std::vector? Sample input: typedef mpl::vector<int, int_<10>, int_<11>, int_<12> > some_vector_c; Thanks, Mostafa

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