November 2011 - Boost-users

[serialization] unwinding "stack" of object during loading
by Igor R 15 Nov '11

15 Nov '11

Hello, Consider the following structure: struct outer { inner_type1 inner1_; inner_type2 inner2_; template<class Archive> void HostPort::load(Archive &ar, const unsigned int version) { ar >> BOOST_SERIALIZATION_NVP(inner1_); ar >> BOOST_SERIALIZATION_NVP(inner2_); } }; Assume that loading of inner1_ throws exception. Is there a way to "unwind" the "stack" of objects gracefully (i.e. to skip until some "end" marker of inner1_), and to proceed loading the next inner object normally? Thanks.

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Dijkstra Visitor examine_edge usage
by giridhar 15 Nov '11

15 Nov '11

Hello All, I have to use Dijkstra's visitor in my project to check a minimum condition on each edge in the shortest path. But I am not sure how to use it with bundled edge properties. Can anyone give me a good overview of how to implement examine_edge() in Dijkstra visitor concept. Below are the details. struct Edgep { int edge_index; int edge_w; std::string edge_name; int capacity; }; Graph as: typedef subgraph< adjacency_list<vecS, vecS, undirectedS, Vertexp, property< edge_index_t, unsigned int, Edgep > > > Graph; Shortest path is based on edge_w and I want to check for the minimum condition on this metric through visitor's examine_edge() function. If someone can give a simple example code for understanding the usage and implementing examine_edge() in Dijkstra visitor concept, then I can go further from there. I actually had a look at it in the documentation but I could not follow that example. Just a simple example would be of great help for me. -- Regards, Giridhar

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[graph] adjacency_list constructor fails, wrong usage?
by Christoph 15 Nov '11

15 Nov '11

Hi, I originally wanted to construct an undirected graph from a directed graph and vice versa. For this purpose i tried to use template <class EdgeIterator> adjacency_list(EdgeIterator first, EdgeIterator last, vertices_size_type n, edges_size_type m = 0, const GraphProperty& p = GraphProperty()) as shown in http://www.boost.org/doc/libs/1_47_0/libs/graph/doc/adjacency_list.html but i do not even manage to construct a graph from the same type with this constructor. What am i missing? Please have a look at the example below. If you uncomment the last two lines, the code will not compile. // begin code #include <iostream> #include <boost/graph/adjacency_list.hpp> #include <boost/graph/graph_utility.hpp> int main(int argc, char** argv) { typedef boost::adjacency_list < boost::listS, boost::vecS, boost::directedS> Dgraph; typedef boost::adjacency_list < boost::listS, boost::vecS, boost::undirectedS> Graph; Dgraph g(5); add_edge (0,1,g);add_edge (2,3,g);add_edge (4,5,g); print_graph (g, boost::get(boost::vertex_index, g)); boost::graph_traits<Dgraph>::edge_iterator i1 = (edges(g)).first; boost::graph_traits<Dgraph>::edge_iterator i2 = (edges(g)).second; // Dgraph g2 = Dgraph (i1, i2, num_vertices (g), num_edges (g)); // print_graph (g2, boost::get(boost::vertex_index, g2)); return 0; } // end code best regards Christoph

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Using an mpl sepquence as a template parameter
by paul Fultz 14 Nov '11

14 Nov '11

Hi, I have class that takes an mpl sequence as its parameter like this: X<mpl::vector<A, B, C> > And I would like to be able to have the class be used without explicitly declaring the mpl sequence like this: X<A, B, C> I know this could be accomplished using variadic template parameters, but I am using an older compiler. I was wondering if there was a macro in boost to do this, such as: template<BOOST_MPL_VARIADIC_PARAM_PACK(T)> class X { typedef mpl::vector<BOOST_MPL_VARIADIC_PARAM_UNPACK(T)> type; }; If a macro is not available, does anyone know how I could write a macro like this? Or what is the default type used for mpl sequences when a type is unspecified? Thanks, Paul

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Using an mpl sepquence as a template parameter
by paul Fultz 14 Nov '11

14 Nov '11

Hi, I have class that takes an mpl sequence as its parameter like this: X<mpl::vector<A, B, C> > And I would like to be able to have the class be used without explicitly declaring the mpl sequence like this: X<A, B, C> I know this could be accomplished using variadic template parameters, but I am using an older compiler. I was wondering if there was a macro in boost to do this, such as: template<BOOST_MPL_VARIADIC_PARAM_PACK(T)> class X { typedef mpl::vector<BOOST_MPL_VARIADIC_PARAM_UNPACK(T)> type; }; If a macro is not available, does anyone know how I could write a macro like this? Or what is the default type used for mpl sequences when a type is unspecified? Thanks,Paul

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How to use boost::iostreams filter directly
by Allan Nielsen 14 Nov '11

14 Nov '11

Hi How can I use boost::iostreams::gzip_decompressor to decompress a sequence of boost::asio::streambuf's? Here is what I had in mind (non-working pseudo code): struct Foo { public: void sinkData(boost::asio::streambuf & buf) { z.write(boost::asio::buffer_cast<const char*>(buf.data()), buf.size()); while(write()); } void flush() { z.flush(); while(write()); } private: bool write() { char buf[1024]; size_t s = z.read(buf, 1024); std::cout << std::string(buf, s) << std::endl; return } gzip_decompressor z; } The sinkData and the flush functions can not be changed. sinkdata() is called a number of times, followed by a single call to flush(). Is boost::iostreams::gzip_decompressor the best library for this purpose, if so how to do it? Otherwise, what could else be suggested? Best regards Allan W. Nielsen

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[smart_ptr] Reinterpret_pointer_cast()?
by Robert Jones 14 Nov '11

14 Nov '11

Even as I ask this I suspect the answer is obvious and I can't see it, but is there any reason why there is no reinterpret_pointer_cast() function for shared_ptr's? Thx, - Rob.

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Using boost Barser to extract data from string
by Gaurav Shah 14 Nov '11

14 Nov '11

> > Hi, > I want to write parser for data I receive from a stock exchange server. > There is no delimeter that define different fields in buffer I receive. > However, it is provided in exchange spec's start and of each field. > How should I write parser for data I recveive? I am new to parser consept > and apprecite your suggestion. > I am putting following example data string just to insist my scenario > > Data my application recveive: > 1001TXPASSWORDSESSION1N > > I need to decode it(as per spec) as: > Messate type: 1001 > UserID: TX > password: PASSWORD > session: SESSION > data: N > > How should I be doing it? > > Thank You, > Gaurav >

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[fusion] more trouble with transform
by Gennadiy Rozental 13 Nov '11

13 Nov '11

Hi, Now I am trying to perform transform which mutates: ------ #include <boost/fusion/container/list/list.hpp> #include <boost/fusion/container/list/convert.hpp> #include <boost/fusion/container/generation/make_list.hpp> #include <boost/fusion/algorithm/transformation/transform.hpp> namespace fusion=boost::fusion; struct C {}; struct B { C make_c() { return C(); } }; struct make_c { template<typename Sig> struct result; template <typename T> struct result<make_c(T&)> { typedef C type; }; template <typename T> struct result<make_c(T)> { typedef C type; }; template <typename T> C operator()(T& t) const { return t.make_c(); } }; int main() { B b1, b2; auto z1 = fusion::make_list( b1, b2 ); auto z2 = fusion::as_list( fusion::transform( z1, make_c() ) ); return 0; } ---- Both gcc and msvc complain like this: test.cpp:29:46: error: passing ‘const B’ as ‘this’ argument of ‘C B::make_c()’ discards qualifiers. What am I missing now? Gennadiy

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Re: [Boost-users] [Spirit-general] Pattern matching with boost
by Alec Taylor 13 Nov '11

13 Nov '11

Thanks Seth, I would certainly like to have UNICODE support, so perhaps the AXE libraries would be a proper solution :) I just need to see if it will work with the MSVC10 compiler, then it will be the solution I am looking for :) The other option is to use something such as iswdigit with the unicode string library: ICU There's a lot more to consider, but it seems like the boost libraries aren't what I require for this project... so I will keep discussion off of these mailing-lists in future. Thanks all for your solutions, Alec Taylor On Sun, Nov 13, 2011 at 3:37 AM, Seth Heeren <bugs(a)sehe.nl> wrote: > On 11/12/2011 03:13 PM, Alec Taylor wrote: > > I am thinking to piece this together using just the stdlib > (std::isdigit &etc)... what do you think? > > By all means. My money is on the hybrid regex+stdlib approach. > > I haven't had the time to evaluate the Axe Library suggested on SO. On first > sight it looked like a regex+native hybrid but with nicer library support. > > But if you have a plan of attack, just go for it. Please, keep in mind that > this is the Boost Spirit general mailing list, and therefore not really > suited for continued discussion in other directions :) > > Cheers, > Seth >

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