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

[function] How to get boost::function parameters, return type.
by Mostafa 12 Apr '11

12 Apr '11

Hi, Is it possible to decompose boost::function into it's "constituent" parameters and return type, a la Boost.FunctionTypes? Thanks, Mostafa

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[boost-user][asio] is packet analysis feasible, and if so how to proceed (references for learning about it needed)
by Ted Byers 12 Apr '11

12 Apr '11

I am investigating the possibility of developing something like a web-shield using boost::asio. What I mean is this. One vulnerability for ecommerce sites is that a session may be hijacked once a user has been validated. Someone intent on fraud may then use that session for a variety of different kinds of fraud. I expect that the lowest level IP address has to be the actual machine making each request (otherwise the attacker would not be able to get the responses to requests he's made), and that one of the things a fraudster may be doing is falsifying the IP addresses in HTTP headers. I also expect some may be using proxy servers to hide their real identity or location. The first thing I need to learn about is whether there are classes or structs defined within asio that facilitate getting packets in a form that would support the sort of packet analysis that may be useful. I would suppose I would need to make a set of classes that collects HTTP headers, to ease examining them particularly for IP data. Ideally, I'd like to be able to examine each major OSI layer (in part, just to learn how they work in real life). And I' like to try to examine the route by which a given HTTP request as arrived at the server that is to handle it, if that is at all possible. And, I'd like to investigate what sorts of patterns ought to be considered with a view toward detecting any form of misbehaviour a fraudster may resort to. If any of this proves feasible, I'd like to create an intelligent 'shield' based on asio that receives incoming http traffic, examines it for misconduct, and if no such behaviour is found just forward the request on to the real server, and if there is evidence of misbehaviour, redirect the user to either static advertizing pages or whatever challenge-response system a merchant may want to try to use in order to reduce his vulnerability to online fraud. I have yet to see any ecommerce software that tries to protect both consumers and merchants from online fraud in this manner, and have spent much of my time writing code that tries to detect fraud, among other problems, after the fact. But it is such a costly process for some merchants, I would like to become more pro-active, to try to prevent it. Alas, although I have written plenty of quantitative code, I have no experience with network programming in C++, so I don't really know what is feasible (but being an R&D kind of guy, I have no qualms about trying to learn stuff that is new to me ;-) Any insights into what is available and what is possible (with URLs to useful resources) would be greatly appreciated. Thanks Ted

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[Boost.MPI] Scattering/Sending a complicated object
by Ryan Lewis 12 Apr '11

12 Apr '11

I have an object which has as a private type a boost::unordered_map<Object,Struct>, and an iterator, which iterates over the map elements. For a given <Object, Struct> map element, the value Struct has a member variable, which is an integer storing a value between 0,...,#NUM_PROCESSORS-1. I'd like to 'scatter' the object by creating new instances of this object on all the threads, where a given <key,value> pair is on processor i, if value has this integer set to be value i. I suppose I could perform a large number of Sends and Receives, i.e. iterate over the complex, and then send a <key,value> pair to the correct worker node every time I find it, but, this seems bad communication wise? Would there be a way to somehow buffer the sends happen at once? Or is there possibly an even better way of doing this? -rhl

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[Serialization] How to serialize a derived type but deserialize it as a base type pointer?
by Jerry 12 Apr '11

12 Apr '11

I know that we can serialize/deserialize a derived type through a base type pointer (using register_type()). But I cannot serialize a derived type and deserialize it through a base type pointer. It seems to me the data type in serialization and deserialization should be extactly the same one. What I want is, Base{...}; Derived : Base{...}; Derived d; boost::archive::binary_oarchive oa(...); oa << d; // serialize a derived object Base *b; boost::archive::binary_iarchive ia(...); ia.register_type(); ia >> b // Deseiralize to a base type pointer I have tried this but it does not work. Is there any way to make this work? Many thanks!!! -- View this message in context: http://boost.2283326.n4.nabble.com/Serialization-How-to-serialize-a-derived… Sent from the Boost - Users mailing list archive at Nabble.com.

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Boost Install fails?
by Dreamcat4 12 Apr '11

12 Apr '11

Hello, I am completely new to Boost framework. However like many others I am finding the initial stage(s) - namely that what is happening during the install seems particularly complicated. I guess most people here have been able to get going with Boost by glazing over the install and "it just works". Other people can run into a myriad of issues. So I guess my problem sits somewhere in-between those two extremes. One thing I cannot vouch for is not knowning (or wanting to know!) what boost is doing, and not seeing anywhere some firm list of requirements (eg system paths for libraries, etc) - I cannot be sure that my system has some misconfiguration somewhere that (is probably) causing this issue. However what is clear to me is that many other people can install boost on *their* systems with no apparent issue. So... whats the problem? In a nutshell, boost will only compile if i am UID=0 (root user / sudo superuser). As a normal, regular user boost install fails with the following error(s): janitors-Mac-mini:boost_1_46_1 id$ ./bootstrap.sh --show-libraries -n Building Boost.Jam with toolset darwin... Failed to build Boost.Jam Consult 'bootstrap.log' for more details bootstrap.log: https://gist.github.com/915620 It doesnt seem to matter the exact version of boost, or even the "CMake" version of boost. They all behave the same way. Whats unfortunate for me especially is that after successfully compiling jam (as root), and chown'ing down all the created files in the boost directory. The same error still seems to occur afterward. For example to compile such selected library. Has anyone seen anything like this? What could be the possible issue here? Is it really normal to compile everything as root?!!? Operating system - Mac OS-X Snow Leopard. Thanks in advance. dreamcat4 dreamcat4(a)gmail.com

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[optional] Comparing boost::optional<T> to NULL yield inconsistent results
by Martin B. 12 Apr '11

12 Apr '11

Hi. I have the following problem: One of our devs used (my_opt != NULL) to check an boost::optional for emptiness. This lead me to write the following test case: ... using namespace std; boost::optional<int> num_opt; boost::optional< std::string > obj_opt; if(obj_opt) { cout << "(3) Object: " << *obj_opt << endl; } // Compiles and does what the user intended - // BUT is this what the boost optional interface intends?? - // namely checking the optional for empty: if(obj_opt != NULL) { cout << "(4) Object: " << *obj_opt << endl; } if(num_opt) { cout << "(1) Integer: " << *num_opt << endl; } // Compiles and crashes, because the user actually // should have written if(num_opt) but, being used to pointers, // wrote the below, which compiles fine, but does not check for empty // but for equality with zero: if(num_opt != NULL) { cout << "(2) Integer: " << *num_opt << endl; } ... I find the behaviour of boost::optional<int> vs. opt<ClassType> highly un-intuitive. Wouldn't it be better if comparing an boost::optional always required to "dereference" it? I checked the headers (Boost 1.44) and sadly there doen't seem to be a preprocessor switch to disable the implicit comparison operators ... I would appreciate if other users could comment on my observations. Thanks! cheers, Martin

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[PBGL] add_edge return type
by Cosimo Calabrese 12 Apr '11

12 Apr '11

Hi to all, I'm trying to use the PBGL lib on VS2010, WinXP, with OpenMPI support; I've compiled without any problem the "dijkstra_shortest_paths.cpp" that I've found in \boost\libs\graph_parallel\example. So I've tried to add a new edge to the graph, and to assign a property value to it. The "classical" mode that I always have used in sequential BGL is: boost::graph_traits<Graph>::edge_descriptor ed; bool inserted; boost::tie( ed, inserted ) = boost::add_edge( boost::vertex( 0, g ), boost::vertex( 0, g ), g ); But the compiler scream... it seems that I can't initialize a tie object in that manner (I've reported the compiler log below). Instead if I first add an edge (with no assignment to tie object), and retrive it with boost::edge function, all works: boost::property_map<Graph, boost::edge_weight_t>::type weightMap = boost::get( boost::edge_weight, g ); boost::graph_traits<Graph>::edge_descriptor ed; bool exists; boost::add_edge( boost::vertex( 0, g ), boost::vertex( 0, g ), g ); boost::tie( ed, exists ) = boost::edge( boost::vertex( 0, g ), boost::vertex( 0, g ), g ); weightMap[ ed ] = 10; What's wrong? Thanks, Cosimo Calabrese. 1>src\main.cpp(75): error C2679: '=' binario: non è stato trovato alcun operatore che accetti un operando destro di tipo 'boost::adjacency_list<OutEdgeListS,VertexListS,DirectedS,VertexProperty,EdgeProperty>::lazy_add_edge'. È anche possibile che non vi siano conversioni accettabili. 1> with 1> [ 1> OutEdgeListS=boost::vecS, 1> VertexListS=boost::distributedS<boost::graph::distributed::mpi_process_group,boost::vecS>, 1> DirectedS=boost::undirectedS, 1> VertexProperty=vertex_prop, 1> EdgeProperty=boost::property<boost::edge_weight_t,float> 1> ] 1> D:\dev\lib\boost\boost/tuple/detail/tuple_basic.hpp(588): potrebbe essere 'boost::tuples::tuple<T0,T1,T2,T3,T4,T5,T6,T7,T8,T9> &boost::tuples::tuple<T0,T1,T2,T3,T4,T5,T6,T7,T8,T9>::operator =(const boost::tuples::tuple<T0,T1,T2,T3,T4,T5,T6,T7,T8,T9> &)' 1> with 1> [ 1> T0=boost::detail::parallel::edge_descriptor<boost::detail::edge_desc_impl<boost::directed_tag,unsigned int>> &, 1> T1=bool &, 1> T2=boost::tuples::detail::tie_traits<void>::type, 1> T3=boost::tuples::detail::tie_traits<void>::type, 1> T4=boost::tuples::detail::tie_traits<void>::type, 1> T5=boost::tuples::detail::tie_traits<void>::type, 1> T6=boost::tuples::detail::tie_traits<void>::type, 1> T7=boost::tuples::detail::tie_traits<void>::type, 1> T8=boost::tuples::detail::tie_traits<void>::type, 1> T9=boost::tuples::detail::tie_traits<void>::type 1> ] 1> durante la ricerca di corrispondenza con l'elenco di argomenti '(boost::tuples::tuple<T0,T1,T2,T3,T4,T5,T6,T7,T8,T9>, boost::adjacency_list<OutEdgeListS,VertexListS,DirectedS,VertexProperty,EdgeProperty>::lazy_add_edge)' 1> with 1> [ 1> T0=boost::detail::parallel::edge_descriptor<boost::detail::edge_desc_impl<boost::directed_tag,unsigned int>> &, 1> T1=bool &, 1> T2=boost::tuples::detail::tie_traits<void>::type, 1> T3=boost::tuples::detail::tie_traits<void>::type, 1> T4=boost::tuples::detail::tie_traits<void>::type, 1> T5=boost::tuples::detail::tie_traits<void>::type, 1> T6=boost::tuples::detail::tie_traits<void>::type, 1> T7=boost::tuples::detail::tie_traits<void>::type, 1> T8=boost::tuples::detail::tie_traits<void>::type, 1> T9=boost::tuples::detail::tie_traits<void>::type 1> ] 1> and 1> [ 1> OutEdgeListS=boost::vecS, 1> VertexListS=boost::distributedS<boost::graph::distributed::mpi_process_group,boost::vecS>, 1> DirectedS=boost::undirectedS, 1> VertexProperty=vertex_prop, 1> EdgeProperty=boost::property<boost::edge_weight_t,float> 1> ]

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How to skip a sub-directory with filesystem3::recursive_directory_iterator in case of exception?
by Tan, Tom (Shanghai) 12 Apr '11

12 Apr '11

> >Again, I tried something like below. >for (recursive_directory_iterator itr(root, ec), itr_end; itr!=itr_end; >) >{ > ... ; > itr.increment(ec); > if(ec) itr.pop(); >} > This time itr.pop() assertion fails because "pop() on >recursive_directory_iterator with level < 1" > >Anybody got some advice? Thanks. For others facing the same problem, I've reported it as a bug and created Ticket #5403(https://svn.boost.org/trac/boost/ticket/5403). A fix was also attached

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[serialization] enable_if managed serialize function
by Noah Roberts 11 Apr '11

11 Apr '11

I want to do something like so: template < typename Archive, typename T > typename boost::enable_if<some_meta_check<T>>::type serialize(Archive & ar, T & rec, unsigned int const) { ar & boost::serialization::base_object<T::type>(rec); } Unfortunately I run into trouble with ambiguous function call referring to a different <Archive,T> version of serialize declared in the serialization library. Does anyone know of a workaround for this?

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[optional] Could (& should) optional be more space efficient?
by David Blaikie 11 Apr '11

11 Apr '11

>From my initial look through boost::optional's implementation, it seems as though it's doing nothing to optimize its space usage in some trivial cases. The first one I was surprised by was optional<T&> - still uses sizeof(struct { T& t; }) + sizeof(bool) space, rather than simply using a pointer to represent both the reference and the unspecified state (using null, since a reference doesn't use that state). Is there a reason for this (perhaps I'm missing something & a reference is smaller than a pointer in certain implementations). Similarly - would it be worth considering optimizing optional<bool> (though, as per the documentation, this is perhaps a little "tricky" at best, owing to the implicit bool of optional itself) to use one byte instead of two? [long term - I'm wondering if a generic "efficient optionality" could be implemented by arbitrary types - privately exposing an extra unused state from their representation for use by optional only. Then, potentially, making versions of (boost/std)::shared_ptr/unique_ptr that would be never-null (only constructible via make_shared like machinery) & optional<shared_non_null_ptr<T>> would then be an explicit representation of the optional situation, but without any overhead - shared_non_null_ptr<T> would simply expose its null state only to optional<shared_non_null_ptr<T>>]

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