August 2008 - Boost-users - lists.boost.org

Decoding hex stream of bytes to binary form
by Mateusz Loskot 21 Aug '08

21 Aug '08

Hi, I've a small function (see below) to convert hex encoded stream of bytes to binary stream. My question is, could anyone suggest equivalent function but implemented with help of Boost libraries? I don't have any particular goal or requirement like better performance, simpler implementation, etc. I'm just curious what Boost components I can use to achieve this kind of tasks. I've scanned the archives but there seem to be not much on encoding/decoding hex string, just: http://lists.boost.org/boost-users/2007/11/32269.php // hex-to-bin function #include <sstream> #include <string> #include <vector> typedef std::vector<unsigned char> ewkb_t; // hexstr [in] - string with hex encoded bytes // bytes [out] - output in binary form void hex_to_bin(std::string const& hexstr, ewkb_t bytes) { bytes.clear(); for(std::string::size_type i = 0; i < hexstr.size() / 2; ++i) { std::istringstream iss(hexstr.substr(i * 2, 2)); unsigned int n; iss >> std::hex >> n; bytes.push_back(static_cast<unsigned char>(n)); } } Best regards, -- Mateusz Loskot, http://mateusz.loskot.net Charter Member of OSGeo, http://osgeo.org

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Wrapping a library
by Alan Baljeu 21 Aug '08

21 Aug '08

I have this library (one class with 700 methods) I want to wrap all the calls, so I can log the calls and do other stuff. Using emacs macros and stuff, I can create a proxy class which has the same signature, but each method calls a C macro which calls the original class method, and does other stuff. For example: void logfunc(char *func) const { OutputDebugStringA(func); } void logarg(int a) // overload for each type of parameter { CString x; x.Format(L"%d", a); OutputDebugString(x); } ULONG GetID(const CKSEntity &pEntity) const { return proxy1(GetID, pEntity); } // repeat for all 700 methods. // Repeat these macros for every count of arg between 0 and 24. #define proxy10(Func, Arg1,Arg2,Arg3,Arg4,Arg5,Arg6,Arg7,Arg8,Arg9,Arg10) \ ( log10(#Func, Arg1,Arg2,Arg3,Arg4,Arg5,Arg6,Arg7,Arg8,Arg9,Arg10), \ thePart.Func( Arg1,Arg2,Arg3,Arg4,Arg5,Arg6,Arg7,Arg8,Arg9,Arg10)) #define log10(Func, Arg1,Arg2,Arg3,Arg4,Arg5,Arg6,Arg7,Arg8,Arg9,Arg10) \ log9(Func, Arg1,Arg2,Arg3,Arg4,Arg5,Arg6,Arg7,Arg8,Arg9), logarg(Arg10) #define log0(Func ) \ logfunc(Func) I'm thinking there must be a better way. I'm thinking BOOST_PP library could abstract the above macros into something concise. However, the library is intimidating. There are lots of features, and I'm not clear on how I should get started. __________________________________________________________________ Looking for the perfect gift? Give the gift of Flickr! http://www.flickr.com/gift/

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[asio] wacky behavior in async_write/async_read
by n0vicd_c0der 21 Aug '08

21 Aug '08

Hi, I am trying to code a simple POP3S client. I am using the boost::asio sockets and SSL wrapper. Somehow, the output from the async_read_util is directed to the input of the async_write. Not sure if the issue is the memory or the order of calls. Any idea? The code snippet is below, but here is the output of my program first (I replaced the IP with x's) bash# ./main 209.85.199.111 995 foo.bar(a)gmail.com pass_in_plain_text Got RES (66) bytes +OK Gpop ready for requests from xxx.xxx.xxx.xxx c20pf1156691rvf.3 Sent REQ: APOP foo.bar(a)gmail.com pass_in_plain_text Got RES (36) bytes -ERR bad command c20pf1156691rvf.3 Sent REQ: STAT Read failed: End of file Exception: End of file and here is the code snippet #include <cstdio> #include <cstdlib> #include <unistd.h> #include <iostream> #include <boost/bind.hpp> #include <boost/asio.hpp> #include <boost/asio/ssl.hpp> #include <boost/asio/detail/throw_error.hpp> enum { max_length = 8192 }; class client { public: client(boost::asio::io_service& io_service, boost::asio::ssl::context& context, boost::asio::ip::tcp::endpoint& endpoint) : socket_(io_service, context) { //connect to the pop3 server socket_.lowest_layer().async_connect(endpoint, boost::bind(&client::handle_connect, this, boost::asio::placeholders::error)); } ~client() { socket_.lowest_layer().close(); } void handle_connect(const boost::system::error_code& error) { if (!error) { //do the SSL handshake socket_.async_handshake(boost::asio::ssl::stream_base::client, boost::bind(&client::handle_handshake, this, boost::asio::placeholders::error)); } else { std::cerr << "Connection failed: " << error << "\n"; boost::asio::detail::throw_error(error); } } void handle_handshake(const boost::system::error_code& error) { if (error) { std::cerr << "SSL Handshaking failed: " << error << "\n"; boost::asio::detail::throw_error(error); } } void write(std::string buffer) { str_req=buffer; boost::asio::async_write(socket_, boost::asio::buffer(str_req), boost::bind(&client::handle_write, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred)); } void handle_write(const boost::system::error_code& error, size_t bytes) { if (!error) { std::cout << "Sent REQ: " << str_req <<std::endl; try{ boost::asio::async_read_until(socket_, buff_, "\r\n", boost::bind(&client::handle_read_until, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred)); }catch(const boost::system::system_error &err){ std::cerr << " code: " << err.code().value() << " :" << err.code().message() << std::endl; } } else { std::cerr << "Write failed: " << error.message() << "\n"; boost::asio::detail::throw_error(error); } } void read() { try{ boost::asio::async_read_until(socket_, buff_, "\r\n", boost::bind(&client::handle_read_until, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred)); }catch(const boost::system::system_error &err){ std::cerr << " code: " << err.code().value() << " :" << err.code().message() << std::endl; } } void handle_read_until(const boost::system::error_code& error, size_t bytes_transferred) { if (!error) { std::cout << "Got RES (" << bytes_transferred<<") bytes\n"; std::cout << &buff_; std::cout << "\n"; } else { std::cout << "Read failed: " << error.message() << "\n"; boost::asio::detail::throw_error(error); } } private: boost::asio::ssl::stream<boost::asio::ip::tcp::socket> socket_; boost::asio::streambuf buff_; //for receiving std::string str_req; //for sending }; int main(int argc, char* argv[]) { try { if (argc != 5) { std::cerr << "Usage: " << argv[0] << " <host> <port> <user> <pass>\n"; return 1; } boost::asio::io_service io_service; boost::asio::ssl::context ctx(io_service, boost::asio::ssl::context::sslv23); ctx.set_verify_mode(boost::asio::ssl::context::verify_none); boost::asio::ip::tcp::endpoint endpoint( boost::asio::ip::address::from_string(argv[1]), atoi(argv[2])); client c(io_service, ctx, endpoint); io_service.run(); //should execute till handshake completes //read the pop3 greeting io_service.reset(); io_service.post(boost::bind(&client::read,&c)); io_service.run(); //send the authentication command std::string str_cmd="APOP " + std::string(argv[3]) + " " + std::string(argv[4]) +"\r\n"; io_service.reset(); io_service.post(boost::bind(&client::write,&c,str_cmd)); io_service.run(); //get how many messages are in the inbox str_cmd="STAT\r\n"; io_service.reset(); io_service.post(boost::bind(&client::write,&c,str_cmd)); io_service.run(); //quit the pop3 session str_cmd="QUIT\r\n"; io_service.reset(); io_service.post(boost::bind(&client::write,&c,str_cmd)); io_service.run(); } catch (std::exception& e) { std::cerr << "Exception: " << e.what() << "\n"; } return 0; } -- View this message in context: http://www.nabble.com/-asio--wacky-behavior-in-async_write-async_read-tp190… Sent from the Boost - Users mailing list archive at Nabble.com.

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[shared_ptr] Implicit cast shared_ptr<derived> to shared_ptr<base>
by Ruediger Berlich 21 Aug '08

21 Aug '08

Hi there, after making what I then thought was a bad mistake, I discovered that the code below actually works (gcc 4.3.1, OpenSUSE 11 64bit, Boost 1.36). I.e., there is an implicit cast from shared_ptr<derived> to shared_ptr<base> to make it fit the function argument, although both represent different types. Is this intended behaviour (i.e. portable) ? I did not find a corresponding description in the docu. Thanks and Best Regards, Ruediger /**************************************************************************/ #include <iostream> #include <boost/shared_ptr.hpp> class base{ public: virtual ~base(){} virtual void print() const { std::cout << "Hello world from base" << std::endl; } }; class derived :public base { public: void print() const { std::cout << "Hello world from derived" << std::endl; } }; void executeBasePrint(const boost::shared_ptr<base>& base_ptr){ base_ptr->print(); } main(){ boost::shared_ptr<derived> derived_ptr(new derived()); // Results in "Hello world from derived" executeBasePrint(derived_ptr); }

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[filesystem] Bugs in path::append ?
by Sachin Garg 21 Aug '08

21 Aug '08

I have following 3 lines of code, is this usage correct? fs::wpath input_path=somepath; fs::wpath output_path=anotherpath; output_path.append(input_path.begin()+7,input_path.end()); The 3rd line gives following error (using Visual Studio 9.0 and boost 1.35.0) C:\Program Files\boost\boost_1_35_0\boost/filesystem/path.hpp(1058) : error C2664: 'boost::filesystem::detail::is_separator' : cannot convert parameter 1 from 'const std::basic_string<_Elem,_Traits,_Ax>' to 'wchar_t' Looking at the code, it does looks like a problem with path.hpp as is_separator expects a wchar_t parameter but append gives it a wstring (unless there some conversion that should have happened but isn't happening. I temporarily changed *first at line 1058 to first->at(0) and this fixed the error.). And there are other errors too like path.hpp(1068) : error C2677: binary '&&' : no global operator found which takes type 'const std::basic_string<_Elem,_Traits,_Ax>' (or there is no acceptable conversion) This too seems valid as path.hpp:1068 'seems' to assume that *first would be same as first->empty() Is this a known issue fixed in 1.36.0? Seems like some presumed conversions are not happening in path.hpp. Or am I making some super dumb mistake in my usage of append()? Sachin Garg

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Sample code for boost::thread - Timed Lockable mutex ?
by Stéphane Vandenbogaerde 21 Aug '08

21 Aug '08

Hello, I want to use timed lockable mutex in boost::thread, but the usage is not so obvious for a beginner. Would there be anywhere a sample code with this kind og mutex ? I have a code which works with a boost::mutex in a consumer/producer queue (code below). The purpose is to have a maximum waiting delay for waitForNotEmpty(). Thanks. ------------------------------------------------------------------------- template <typename T> class MTBornedQueue { public: .... bool waitForNotEmpty() { if (!m_container.empty()) return true; boost::mutex::scoped_lock lock(m_accessMutex); m_notEmpty.wait(lock, boost::bind(&MTBornedQueue<value_type>::isNotEmpty, this)); return true; } ... private: bool isNotEmpty() const { return m_unread > 0; }; size_type m_unread; container_type m_container; boost::mutex m_accessMutex; boost::condition m_notEmpty; }

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boost::graph issues.
by Raindog 21 Aug '08

21 Aug '08

Hello, This will be the 2nd time I've tried to use boost::graph in a project, the first time I ended up scrapping the effort and using a different graph implementation because of performance reasons, but I was also considering scrapping it for the reasons I have listed here. My newest project will be using much smaller graphs. First, I *want* to use bgl, the problem I have is that it is by far the most complex and difficult to use library I have ever seen. I equate it to something harder than COM using only C. The majority of my difficulties with BGL are related to the extensive use of template magic that does two things for me: makes code impossible to follow and secondly, it makes debugging even more difficult. For example, someone tell me from looking at this, what *values* will actually be passed to astar_search: astar_search (g, s, h, choose_param(get_param(params, graph_visitor), make_astar_visitor(null_visitor())), choose_param(get_param(params, vertex_predecessor), p_map), cost, distance, weight, index_map, color, choose_param(get_param(params, distance_compare_t()), std::less<C>()), choose_param(get_param(params, distance_combine_t()), closed_plus<C>()), choose_param(get_param(params, distance_inf_t()), std::numeric_limits<C>::max BOOST_PREVENT_MACRO_SUBSTITUTION ()), choose_param(get_param(params, distance_zero_t()), C())); } I would be hard pressed to believe that anyone can answer that in a short amount of time even assuming you have memorized all of the template parameters of g and s and even h. On with more issues. One of the biggest issues I have is that the the property_map concept is exceptionally vague and exceedingly difficult to work with. For example, I have created a graph, it's concise typedef: typedef boost::adjacency_list < boost::vecS, boost::vecS, boost::directedS, boost::property<boost::vertex_name_t, Ogre::Vector3>, boost::property<boost::edge_weight3_t, edge_cost> > GraphT; Because of the use of free functions, it's hard to quickly distinguish "get" calls on a property_map from "get" calls on a graph. Additionally, the property_map installation and retrieval to and from a BGL graph is also hard to follow. One might see the following code in the examples directory of bgl: typename property_map<Graph, edge_mycapacity_t>::const_type capacity = get(edge_mycapacity, G); typename property_map<Graph, edge_myflow_t>::const_type flow = get(edge_myflow, G); Where "edge_mycapacity" is an enum; and how exactly enums of the same value can be used to look up different property_maps from the graph is a gaping hole left in the documentation and I still have no idea how it works. Another example is the following: get(vertex_color_t(), g, vertex(2,g)) Here we seem to be left to our imaginations as to how this works. "get" in this case is obviously operating on a graph in this call, but why are we no longer using an enum and instead constructing a temporary "vertex_color_t". Looking at the definition of "get", we see the following: template<typename OutEdgeListS, typename VertexListS, typename DirectedS, typename VertexProperty, typename EdgeProperty, typename GraphProperty, typename EdgeListS, typename T, typename Bundle, typename Key> inline T get(T Bundle::* p, adjacency_list<OutEdgeListS, VertexListS, DirectedS, VertexProperty, EdgeProperty, GraphProperty, EdgeListS> const & g, const Key& key) { return get(get(p, g), key); } Hmm, looks like we'll need to look further. I personally am not knowledgeable enough in template magic to make sense of the majority of the BGL source, for me there are way too many things to keep track of in order to be able to completely follow the code. I can't follow very well 100 character variable declarations. So, for some real questions and to end the rant. 1. What language mechanism is allowing property_maps to be stored and retrieved from an instance of a graph? How does "BOOST_DEF_PROPERTY(edge, index)" work exactly? 2. What *is* the required interface for a property_map? get,put, operator[] of course, but the BGL properties appear to function nothing like the example given in the documentation. 3. Why is using get(p,g) better than using myPropMap.get_from(myGraph) and myGraph.get_property_map(prop_map_type) and myGraph.get_edge(edge_descriptor). What benefit does the chosen method provide? 4. The edge property example contains the following: typedef property<edge_mycapacity_t, int> Cap; typedef property<edge_myflow_t, int, Cap> Flow; typedef adjacency_list<vecS, vecS, bidirectionalS, no_property, Flow> Graph; But accesses the Cap property_map as if it is directly associated with the graph, not a nested property of Flow: typename property_map<Graph, edge_mycapacity_t>::const_type capacity = get(edge_mycapacity, G); Can someone explain how that works in better detail? Thanks, Josh PS. This is the 4rd time i've attempted to send this message as I've not seen it yet appear on the list. The 1st 2 attempts were rejected as I had not yet completed subscription process.

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AIX 5.3 xlC error on ptr_list.hpp
by Gary Fu 21 Aug '08

21 Aug '08

Hi, The simple test program a.cpp below has no problem to compile on linux g++, but failed on AIX xlC compiler. Does any one know if the problem is related to the xlC compiler or the ptr_list.hpp file ? Thanks, Gary 4:43pm 19 Ggfu@sds:~/tmp> xlC_r -I/home_dir/Ggfu/BOOST/boost_1_36_0 -c a.cpp "/home_dir/Ggfu/BOOST/boost_1_36_0/boost/ptr_container/ptr_list.hpp", line 44.9: 1540-0400 (S) "boost::ptr_list::release" has a conflicting declaration. "/home_dir/Ggfu/BOOST/boost_1_36_0/boost/ptr_container/ptr_list.hpp", line 44.9: 1540-0425 (I) "release" is defined on line 44 of "/home_dir/Ggfu/BOOST/boost_1_36_0/boost/ptr_container/ptr_list.hpp". ----------------- a.cpp #include <boost/ptr_container/ptr_list.hpp> boost::ptr_list< std::string > y; int main() { return 0; }

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How to find a sorting permutation
by Zeljko Vrba 21 Aug '08

21 Aug '08

I have a vector of element V that needs to be sorted. I want to also produce a permutation vector P which reflects the element's position in the original vector. P is initialized with identity permutation (P[i] == i). 1st possibility: code my own sorting algorithm, and swap elements of P along with swapping elements of V. This I want to avoid, if at all possible. 2nd possibility: copy elements of V into new vector V' holding pair<T, size_t> and sort that. (pair holds the original element as well as its starting position in the vector, i.e. .second is again initialized to identity permutation.) Drawback: extra space and time spent on copying to V'. 3rd possibility: sort elements of P with less_than doing lookups into V to do its comparison. Drawback: while P holds the correct result, V is left unsorted; I have to do another pass through V and swap elements according to the permutation recorded in P, which is not trivial to do in-place. 4th possibility: I'm not sure whether it'd work: have a separate compilation unit that will provide function sort_vector_of_T, which will take references to V, T and also provide a specialization of std::swap for T which will then also swap elements of P). (Separate compilation unit is needed because I don't want to *globally* redefine std::swap for T) Is there some non-obvious, efficient and elegant way of achieving what I want?

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Implementation question about boost::circular_buffer and allocator
by Peter Barker 21 Aug '08

21 Aug '08

Hello, I've been going through the Boost libraries and encountered boost::circular_buffer. My question is not with the operation of Boost.Circular Buffer as-such, but about how the instantiation of it works without specifying the allocator. The introductory example in the documentation(http://www.boost.org/doc/libs/1_35_0/libs/circular_buffer/doc… contains the following line: // Create a circular buffer with a capacity for 3 integers. boost::circular_buffer<int> cb(3); But looking at the header file base.hpp in the circular_buffer directory, we have the following: template <class T, class Alloc> class circular_buffer { ...... }; The Alloc template parameter is not a default one, so I can't understand how we can instantiate cb in the example? Apologies if this is not strictly boost-user related. Regards, Jim

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