March 2009 - Boost - lists.preview.boost.org

[soc2009] Boost is in summer of code 2009: attention mentors
by troy d. straszheim 18 Mar '09

18 Mar '09

All, We've just been accepted as an organization in Google's Summer of Code 2009. Per this user's guide: http://socghop.appspot.com/document/show/program/google/gsoc2009/userguide those who have volunteered to mentor need to create a site-wide profile, and apply to mentor for Boost, then I'll click you in. Student applications start March 23rd. Until then: - Plan your application. - Brainstorm about project ideas on the mailing lists and IRC. - Familiarize yourself with existing work in the areas you are interested in by reading the mailing list archives and playing with existing Boost libraries. - Make proposals and get feedback. More as I get it. Thanks to Google and their Melange dev team. Looking forward to a good GSOC 2009. -t

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Boost::Format add-on
by Joel Falcou 18 Mar '09

18 Mar '09

Who is in charge of Format maintenance ? I would like to propose a simple patch to add an accessor to the number of arguments expected by the formating : int args() const { return num_args_; } Regards

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[array] change proposal for the c_array() function
by herve martin 18 Mar '09

18 Mar '09

Hi, I'm new in this mailing list .My interest are embedded software and code reuse. I would submit a simple change request in the boost::array library. The boost::c_array() function is expected to cast a boost::array<T,N> into a C-array but actually the returned type is a T* which is not exactly a reference on a C-array. to keep track of the static size and make sizeof( myarray.c_array() ) returning the real size of the C-array, I suggest to change: T* c_array() { return elems; } into T (&c_array())[N] { return *(T(*)[N]) elems; } by the way, I have developed a function helper array_cast<> whose purpose is to: * make a bit more friendly the syntax when casting to a C-array * check consistency between size of the input type and size of the target C-array for example, { long titi; char (&test)[4] = utils::array_cast<char>( titi ); test[0] = 0; } assuming that long is 32 bit long and char is 8 bit long, 'test[0]' is now a reference on the 1st byte of 'titi'. Moreover declaring test as a char(&)[5] would have failed in compiling since size of both types are not suitable (but the function provides some other way to force cast when sizes are not compatible) do you think that there could be any interest to include this function in boost library ? thanks, herve

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Why my subexpression doesn't work in Regex
by Qihong Wang 18 Mar '09

18 Mar '09

Hello, I'm a new boost and regex user. I tried a c++ regex sample as follows regex pattern("banan\\(an\\)*a"); string str = "bananana"; if(regex_match(str, pattern)) cout<<"---- pattern matched ----"<<endl; else cout<<"---- pattern unmatched ----"<<endl; To my surprise, the it printed out pattern unmatched. If I change str to "banan(an)a", the result is pattern matched. Feels like boost.Regex doesn't treat ( ) as subexpression. Any idea? Thanks, Qihong Wang

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[lexical_cast] Strange behaviour
by Robert Jones 18 Mar '09

18 Mar '09

Trying again 'cos I mucked up the code last time! This code #include <iostream> #include <boost/lexical_cast.hpp> int main() { using namespace std; try { unsigned int u=boost::lexical_cast<unsigned int>("-1"); cout << u << '\n'; } catch(const std::exception&) { cout << "Exception" << '\n'; } } produces 4294967295 on MSVC7 & 8 rather than an exception. Is it supposed to do this? Rob.

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[utility] new auto_buffer class --- RFC
by Thorsten Ottosen 18 Mar '09

18 Mar '09

Dear all, For a long time I have been missing this utility in my own work, and in boost related stuff too. I think there are a number of libraries in boost that can benefit from this utility. Libs like boost.format can be quite a bit more effective. So can logging libraries. etc. Basically boost::auto_buffer<T,N> is a C++ version of variable lenght array (from C99). It's based on Matthew Wilson's stlsoft::auto_buffer, which can be found described in his book "Imperfect C++". I have changed a few things though: // - no swap() and resize() provided // - works with allocators from Boost.Interprocess // - do not store T[N] on the stack, as this is bad when the // type has a non-trivial default constructor. // - handless non-pod types in an exception-safe manner // - has a fixed capacity, but a non-fixed size // - provides a non-growing (thus inlineable) push_back() Comments are most welcome. best regards -Thorsten

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reference to ‘_1’ is ambiguous
by Sandeep Gupta 18 Mar '09

18 Mar '09

Hi, This problem has appeared before on the list but in a different context. The following code std::vector<int> myvec; for_each(myvec, std::cout<<_1<<' '); gives the error: Serializer.h:78: error: reference to ‘_1’ is ambiguous /home/sandeep/Computing/boost_1_38_0/boost/lambda/core.hpp:69: error: candidates are: const boost::lambda::placeholder1_type& boost::lambda::<unnamed>::_1 /home/sandeep/Computing/boost_1_38_0/boost/bind/placeholders.hpp:54: error: boost::arg<1> <unnamed>::_1 Serializer.h:78: error: reference to ‘_1’ is ambiguous I believe boost/bind is getting included indirectly via some other library. I have tried several modification but none seem to work as I was quite reluctant to post a third mail on the list. Thanks, sandep

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pointer to member function of multi_index
by Sandeep Gupta 18 Mar '09

18 Mar '09

Hi, I am sure this is due to some trivial mistake; the statement to create a pointer member function insert of multi_index container fails in the following code: typedef multi_index_container< std::pair<int,int>, indexed_by< ordered_unique<member<pair<int,int>, int, &pair<int, int>::first> > > > mic; std::pair<mic_index::iterator, bool> (mic_index::*fn)(pair<int,int>) = &mic_index::insert; //compile error The error is due to mismatch in signature as given in the error: std::pair<boost::multi_index::detail::bidir_node_iterator<boost::multi_index::detail::ordered_index_node<boost::multi_index::detail::index_node_base<std::pair<int, int>, ... std::pair<boost::multi_index::detail::bidir_node_iterator<boost::multi_index::detail::ordered_index_node<typename SuperMeta::type::node_type> >, bool>... If need be I can post full error message. Appreciate any suggestions. Thanks sandeep

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correct usage of bind (pls ignore last email)
by Sandeep Gupta 17 Mar '09

17 Mar '09

Hi, The code below tries to chain function ft1 (argument is a pair) with function buildPair (returns a pair). template<typename X, typename Y> std::pair<X, Y> buildPair(X x, Y y) { std::pair<X,Y> apair(x,y); return apair; } int main() { typedef boost::function<void (std::pair<int,int>)> FuncType1_t; std::vector<std::pair<int,int> > myvec; FuncType1_t ft1 = bind(&std::vector<std::pair<int,int> > ::push_back, &myvec, _1); typedef boost::function<void(std::pair<int,int>)> FuncType2_t; FuncType2_t ft2 = bind(ft1, bind(buildPair<int,int>,_1,_2)); //compile fails return 0; } This fails. The problem however vanished if I replace the declaration "FuncType3 ft2..." with bind(ft1, bind(buildPair<int,int>,_1,_2))(3,5); So my question is what is correct type of bind(ft1, bind(buildPair<int,int>,_1,_2)); Thanks sandeep

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correct usage of bind
by Sandeep Gupta 17 Mar '09

17 Mar '09

Hi, Both the statements below bind function buildPair. While the first works the other fails. What could be a possible fix. Thanks in advance. //---- Function to be used by bind ------------------------- template<typename X, typename Y> std::pair<X, Y> buildPair(X x, Y y) { std::pair<X,Y> apair(x,y); return apair; } (std::cout<<buildPair(_1,_2).first<<' ')(1,2); ///--compiles fine--------- (bind(buildPair,_1,_2))(3,5); ///-fails------------ Thanks sandeep

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