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Raw sockets for Layer 2 communications
by Carlos Guimarães 31 Jan '12

31 Jan '12

Hi, I've been looking for any way to send L2 messages (with no transport protocol) using Boost. As long as I could find, Boost libraries support raw sockets, however it must have a transport protocol (like IP) associated. Is this right?There is any way to send a pure L2 packet? Best regards, Carlos Guimarães

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boost 1.49 beta tar problems
by Avi Bahra 31 Jan '12

31 Jan '12

I am trying boost 1.49 beta1 on the different platforms. This builds fine on linux variants However on AIX and HPUX I get. "directory checksum error" when untarring ? I can untar boost 1.48 and all previous boost version on these platforms, so guessing there been a change in the tar used ? Best regards, Ta, Avi

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Boost.Regex: regex_replace with named captures/groups
by norulez＠me.com 31 Jan '12

31 Jan '12

Hi @all, does boost's regex_replace not recognize named captures/groups or did I something wrong? std::string date = "2012/01/30"; std::string replace = "\5\g{separator}\4\g{separator}\1\2"; // should be => 30/01/2012 boost::regex rx("^(19|20)(\d\d)(?<separator>[/.])(0[1-9]|1[012])\g{separator}(0[1-9]|[12][0-9]|3[01])$"); std::string replaced = boost::regex_replace(date, rx, replace); The content in "replaced" is now "30\g{separator}01\g{separator}2012" Thanks in advance Best Regards NoRulez

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[Thread] code segfaults/hangs when being called from matlab, not when run standalone
by Dougal Sutherland 31 Jan '12

31 Jan '12

Hi all, I have some code using boost::thread that works fine when it's called directly from a main() function, but (almost) always segfaults and/or hangs forever when called from a Matlab mex interface. I don't know whether that's due to the Matlab interface breaking something about boost::thread or if the different environment is revealing a flaw with my code. Here's a simplified version of the code I'm using. (This same question is also posted on stackoverflow at http://stackoverflow.com/q/9011780/344821-- the code is prettier, and you can get some stackoverflow reputation out of me if you answer there.) #include <cstdlib> #include <queue> #include <vector> #include <boost/thread.hpp> #include <boost/utility.hpp> #ifndef NO_MEX #include "mex.h" #endif class Worker : boost::noncopyable { boost::mutex &jobs_mutex; std::queue<size_t> &jobs; boost::mutex &results_mutex; std::vector<double> &results; public: Worker(boost::mutex &jobs_mutex, std::queue<size_t> &jobs, boost::mutex &results_mutex, std::vector<double> &results) : jobs_mutex(jobs_mutex), jobs(jobs), results_mutex(results_mutex), results(results) {} void operator()() { size_t i; float r; while (true) { // get a job { boost::mutex::scoped_lock lk(jobs_mutex); if (jobs.size() == 0) return; i = jobs.front(); jobs.pop(); } // do some "work" r = rand() / 315.612; // write the results { boost::mutex::scoped_lock lk(results_mutex); results[i] = r; } } } }; std::vector<double> doWork(size_t n) { std::vector<double> results; results.resize(n); boost::mutex jobs_mutex, results_mutex; std::queue<size_t> jobs; for (size_t i = 0; i < n; i++) jobs.push(i); Worker w1(jobs_mutex, jobs, results_mutex, results); boost::thread t1(boost::ref(w1)); Worker w2(jobs_mutex, jobs, results_mutex, results); boost::thread t2(boost::ref(w2)); t1.join(); t2.join(); return results; } #ifdef NO_MEX int main() { #else void mexFunction(int nlhs, mxArray **plhs, int nrhs, const mxArray **prhs) { #endif std::vector<double> results = doWork(10); for (size_t i = 0; i < results.size(); i++) printf("%g ", results[i]); printf("\n"); } If I compile and run this directly (with gcc or clang and -DNO_MEX), it always completes successfully. If I run this through Matlab's mex interface and link to a release-variant boost (I've tried 1.48.0 on OSX and both 1.40 and 1.33.1 on CentOS), I get a segfault. On 1.48.0, this is trying to access a pointer that's near 0 inside boost::thread::start_thread from inside of t1's constructor; on 1.33.1 and 1.40, it's inside pthread_mutex_lock being called from t1.join(). If I instead link to a debug-variant boost (1.48 on OSX or 1.33.1 on CentOS -- the machine with 1.40 installed doesn't have a debug variant), it hangs forever inside t1.join(), though the threads have completed successfully, with results containing the expected elements that were calculated as rinside Worker. (On OSX, these are different numbers than are printed by the standalone version, but they're still consistent between threads.) Am I doing something stupid that's causing this, or is this somehow due to something on the matlab end? I'm pretty new to C++ and boost and so it might well be something dumb that I did, but I don't know what that could be. I also don't really have any ideas on how to proceed from here in terms of debugging, especially since the segfaults only occur when there are no debugging symbols in the boost libraries themselves around to help figure out what's going on. My only real idea is to try this without boost::thread and using pthreads directly, but even if that worked it's nonideal since I'd also like to support Windows. Thanks, Dougal

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[lexical_cast][variant] Compile failed when included boost.variant.
by Tianjiao Yin 31 Jan '12

31 Jan '12

Hello, all: I met a strange compile error, this code will reproduce the problem:: #include <boost/lexical_cast.hpp> #include <boost/variant.hpp> #include <iostream> namespace foo { struct bar {}; } std::ostream& operator << (std::ostream& out, foo::bar) { return out << "BAR"; } int main() { boost::lexical_cast<std::string>(foo::bar()); } However, if I just remove that unused include boost.variant, it works:: #include <boost/lexical_cast.hpp> //#include <boost/variant.hpp> #include <iostream> namespace foo { struct bar {}; } std::ostream& operator << (std::ostream& out, foo::bar) { return out << "BAR"; } int main() { boost::lexical_cast<std::string>(foo::bar()); } Another solution is put that "operator<<" in namespace foo:: #include <boost/lexical_cast.hpp> #include <boost/variant.hpp> #include <iostream> namespace foo { struct bar {}; std::ostream& operator << (std::ostream& out, foo::bar) { return out << "BAR"; } } // namespace foo int main() { boost::lexical_cast<std::string>(foo::bar()); } Anyway, what is boost.variant's business here? Won't that fail to compile, or am I missing something? BTW, I'm using boost 1.48.0 and gcc 4.6.2 in Linux 3.2.2. Regards, Tianjiao

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I need a sample Asio asynchronous client to read&write into sockets and stdin&stdout.
by vincegata 30 Jan '12

30 Jan '12

Hello, I am writing a client application that reads and writes data into a remote server. Currently the communication is done using synchronous (blocking) sockets. I am running Ubuntu and using C++. I need to re-write this app so it will asynchronously read & write into sockets and stdin/stdout, I also need to send a heartbeat signal if there wasn't any communication with the server for 60 seconds. I am new to Asio, I went through tutorial and looked at the examples such as asynchronous timer and client chat but they are not all that I need. Could someone point me to a sample Asio application that does what I need. Thank you!

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Conversion from numeric type to const char*
by Claude 30 Jan '12

30 Jan '12

What is the better way for convert a numeric type into a const char *? I use: (boost::lexical_cast<std::string>(myNumericVar)).c_str() It is a good idea? -- View this message in context: http://boost.2283326.n4.nabble.com/Conversion-from-numeric-type-to-const-ch… Sent from the Boost - Users mailing list archive at Nabble.com.

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[Property_tree] using find to find a key
by Sean Farrow 30 Jan '12

30 Jan '12

Hi: I am declaring a property_tree, pulating this with an ini file. I then need to find out whether a section (key) is present, so I'm doing: boost::property_tree::ptree::assoc_iterator it =IniTree.find(key); if (it !=boost::property_tree::ptree::not_found) using visual c++ 2010 I get an error c2678, telling me that no operand is able to use these two values. Can someone please tell me what I'm doing wrong, as I can normally do this for std::vectors etc! Cheers Sean.

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multi_array: How to get the extends?
by Helmut Zeisel 30 Jan '12

30 Jan '12

How can I get the extends of a multi_array? E.g. I have boost::multi_array<double, 3> a(boost::extents[n0][n1][n2]); Are there functions like a.extend(0) returning n0, a.extend(1) returning n1, and a.extend(2) returning n2 (or similar)? Helmut -- "Feel free" - 10 GB Mailbox, 100 FreeSMS/Monat ... Jetzt GMX TopMail testen: http://www.gmx.net/de/go/topmail

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copy a range to ostream
by Neal Becker 29 Jan '12

29 Jan '12

With all the nice boost libraries, is there a modern idiom to copy a range to an ostream? I was thinking range/algorithm/copy could be useful. What I'd really like to do is: std::vector<some type> x; range::copy (x, std::cout); Of course there would also need to be a way to specify formatting, at least insertion of whitespace.

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