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questions about recursing a directory tree
by Zsolt Ero 25 Nov '10

25 Nov '10

I am just learning C++ and for a first project I would like to write a program which goes recursively through a directory tree and returns the newest and the oldest file date. I have been following the documentation, but I couldn't really find a working example for a recursive algorithm. Shell I start by using this code from the v2 documentation? ---------------------------------- bool find_file( const path & dir_path, // in this directory, const std::string & file_name, // search for this name, path & path_found ) // placing path here if found { if ( !exists( dir_path ) ) return false; directory_iterator end_itr; // default construction yields past-the-end for ( directory_iterator itr( dir_path ); itr != end_itr; ++itr ) { if ( is_directory(itr->status()) ) { if ( find_file( itr->path(), file_name, path_found ) ) return true; } else if ( itr->path().filename() == file_name ) // see below { path_found = itr->path(); return true; } } return false; } ------------------------------- The other way I figured out is with recursive_directory_iterator: ------------------------------ #include "boost/filesystem.hpp" #include <iostream> namespace fs = boost::filesystem; fs::recursive_directory_iterator end; fs::recursive_directory_iterator dir("e:\\docs"); void main() { for ( ; dir != end; ++dir ) { std::cout << *dir << std::endl; } } ------------------------------- Is it safe to use recursive_directory_iterator on a really big directory tree? I mean is it going to copy the whole tree into memory? Does it walk through the whole directory tree the moment it's called, or it only accesses the disk on a ++ operation one-by-one? I still haven't looked into how to compare two files' date, but could you give a hint about which function shell I use? Is it possible to use just a simple < or > operation on file dates, or I need to write manually if year1 > year2 and if month1 > month2, etc? Thanks in advance, Zsolt

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asio UDP async receive question - how to do this properly?
by Ákos Maróy 25 Nov '10

25 Nov '10

Hi, I wonder what the proper pattern is to receive messages, store them, and process them in an async manner? What I'm trying to do, and which doesn't work: - receive the packets in an async call - copy the data over - start to receive again after copying - store the data using a producer - consumer pattern, using a mutex - process the data in another thread (which is the consumer in the pattern) but, this doesn't seem to work, as a lot of packets are lost. my assumption is that because the handler function blocks on the mutex, and returns 'late', packets received in the meantime are lost forever. but: how to do this properly? I have a small sample here: http://pastebin.com/NnbK1T7G , which is based on one of the asio examples. the sample code is quite simple: - it allows sync sending of messages (strings) - it allows async reception of such messages - it will put each received message into a vector, which is guarded by a mutex - another thread will process messages from this vector on a regular basis, which processing is also guarded by a mutex. if I compile & run the sample, I get: ./async_asio b sent 20000 messages a received 1981 messages which is a profound loss of packets. as seen in the sample, after the receive handler is called, the recieved message is copied over, and socket::async_receive_from() is called ASAP. I don't see what else would need to be done to have all messages received. If I remove the processing of messages in threa_func(), the results are markedly better: ./async_asio b sent 20000 messages a received 19963 messages increasing the sleeping time at the end does no good - it seems the messages were lost already. Akos

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A question about boost thread
by x57978 25 Nov '10

25 Nov '10

Hi, Does somebody know whether the boost thread can set the affinity like other thread? Thanks. Hongmiao

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[asio] strange behaviour on android
by Igor R 24 Nov '10

24 Nov '10

Hello, Recently I ported my application to Android, and after some testing I encountered the following strange behavior. Long story short: I send text to a peer and sometimes it gets "cut" in the beginning. like this: aaa\r\nbbb\r\nccc\r\nddd\r\n becomes \nccc\r\nddd\r\n I checked with sniffer, and ensured that the problem is really in my application. To send the text I use the following simple approach: * io_service::run is always invoked from one thread * the data comes from another thread and gets posted to the io_service thread: void connection::send(const std::string &str) { io_.post(boost::bind(&connection::doSend, shared_from_this(), str)); } * then it's streamed into asio::streambuf: void connection::doSend(const std::string &str) { std::ostream(&output_).write(str.c_str(), str.length()); } * and finally async_write is invoked, IF it's not in progress: if (!activeWrite_) { activeWrite_ = true; async_write(m_output, boost::bind(&connection::sent, shared_from_this(), asio::placeholders::error)); } (of course, in sent() handler async_write is re-activated, if needed). I understand that I add data to the streambuf, while async_write is in progress, but it's done in the same thread, and seems to be legitimate. The above approach works on Windows and on some other platforms, it was stress-tested, and never showed any problem. OTOH, on Android the above issue happens very frequently (~20% of events). The only difference here is that I compiled my project with BOOST_ASIO_DISABLE_FENCED_BLOCK, because otherwise the linker complains it doesn't see definitions of some gcc synchronization intrinsics. Is it possible that this's the problem? As far as I see, fenced_block is used when a completion handler is called, so I can't see how it can be connected to my problem... Anyway, I'd appreciate any idea. Thanks.

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cross platform high resolution timer
by Sean Farrow 24 Nov '10

24 Nov '10

Hi: Does boost contain a cross platform high resultion timm that allows a function to run every resolution. Something that is equivalent to the win32 multimedia timer. Any help appreciated. Sean.

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[Interprocess] Different outputs under bash and gdb
by Aditya Gadre 24 Nov '10

24 Nov '10

Dear all, I have a question about proper use of Boost.Interprocess for sharing custom C++ classes. I recently started using Boost.Interprocess and have been successful in sharing boost::array, std::vector<float>, std::vector< boost::array<float, 2> > etc using boost::interprocess::managed_shared_memory and boost::interprocess::allocator. Currently, I am trying to share a custom matrix class that is used to hold data in a tabular format. The Matrix class (attached header file Matrix.hpp) is a simple wrapper class that uses std::vector to store objects and provides functions to find items using linear and matrix indexing. I have modified a boost::interprocess example program to try out sharing the Matrix class (attached file test_matrix_shm.cpp). The parent process creates a managed memory segment along with a Matrix in the shared memory. The child process accesses the shared memory and successfully finds the Matrix object. However, when I run the program under bash, the output of the child process shows wrong data. However, if I run the same program under gdb, then every time the child process shows correct Matrix data as was set by the parent process (please find sample outputs below). I am really not sure what would cause this behavior. I would appreciate any input in this regard. * bash output * parent process Matrix size = 2 x 2 0 1 2 3 child process Matrix size = 2 x 2 -1.2522e-41 -1.25486e-41 -1.2571e-41 -1.25949e-41 child returning parent returning * gdb output * GNU gdb (GDB) SUSE (7.1-3.12) (gdb) run Starting program: test_matrix_shm parent process Matrix size = 2 x 2 0 1 2 3 Detaching after fork from child process 2548. child process Matrix size = 2 x 2 0 1 2 3 child returning parent returning Program exited normally. Thanks - Aditya

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[boost::asio] link errors using boost 1.44.0 on 32-bit
by Samir Kharchi 24 Nov '10

24 Nov '10

Hi, I am mainly using boost::asio and I get a link error when I try to build my project on 32-bit release VC8.0 saying (The according 32-Bit libs are correctly included): error LNK2019: Verweis auf nicht aufgelöstes externes Symbol ""class boost::system::error_category const & __cdecl boost::system::system_category(void)" (?system_category@system@boost@@YAABVerror_category@12@XZ)" in Funktion ""class boost::system::error_category const & __cdecl boost::system::get_system_category(void)" (?get_system_category@system@boost@@YAABVerror_category@12@XZ)". error LNK2001: Nicht aufgelöstes externes Symbol ""class boost::system::error_category const & __cdecl boost::system::system_category(void)" (?system_category@system@boost@@YAABVerror_category@12@XZ)". However, compiling my project in 64-Bit release works just fine (according 64-bi libs included) and I don´t get these errors. Anybody knows what´s going on here? :-/ I searched the boost list for previous problems but none of the topics I found helped. Thank you in advance Samir

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undefined references '__sync_fetch_and_add_4 ' for Boost_1_39_0 on Alpha platform
by Yan Wu 24 Nov '10

24 Nov '10

Hi, I got an error when building OpenOffice.org on Alpha EV6 platform, the error log is as following: Compiling: comphelper/unxlngaxp.pro/misc/comphelp4gcc3_version.c Making: comphelper.lib Making: libcomphelp4gcc3.so ../unxlngaxp.pro/slo/enumberablemap.o: In function 'comphelper::EnumerableMap::initialize(com::sun::star::uno::Sequence<com::sun::star::uno::Any> const&)': '__sync_fetch_and_add_4' undefined reference ./unxlngaxp.pro/slo/enumberablemap.o: In function 'comphelper::EnumerableMap::initialize(com::sun::star::uno::Sequence<com::sun::star::uno::Any> const&)': '__sync_fetch_and_add_4'undefined reference ../unxlngaxp.pro/slo/enumberablemap.o: In function 'comphelper::EnumerableMap::initialize(com::sun::star::uno::Sequence<com::sun::star::uno::Any> const&)': '__sync_fetch_and_add_4'undefined reference ../unxlngaxp.pro/slo/enumberablemap.o: In function 'comphelper::EnumerableMap::initialize(com::sun::star::uno::Sequence<com::sun::star::uno::Any> const&)': '__sync_fetch_and_add_4'undefined reference ../unxlngaxp.pro/slo/enumberablemap.o: In function 'comphelper::EnumerableMap::initialize(com::sun::star::uno::Sequence<com::sun::star::uno::Any> const&)': '__sync_fetch_and_add_4'undefined reference ../unxlngaxp.pro/slo/enumberablemap.o: more undefined references to '__sync_fetch_and_add_4' follow collect2: ld returned 1 exit status dmake: Error code 1: while making '../unxlngaxp.pro/lib/libcomphelp4gcc3.so' The <boost/shared_ptr.hpp> of Boost_1_39_0 is used here. Is this a bug on Boost_1_39_0 ? and is there already a fix for it? Best Regards, Yan

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boost thread query
by Sean Farrow 24 Nov '10

24 Nov '10

Hi: I have two threads that are started by a class created by the applications main thread. Can the thread function be a private member of that class or does it need to be public? When the application exits I need the threads to be notified and exit. What is the best way of handling this? I need this to be cross platform but in windows I would have used a waitforSingleObject and signalled the event when the main thread wants to exit. Could I use a condition for this, and do a do while loop waiting on the condition to be notified, if I do this do I need a mutex just for the condition? Any help appreciated. Cheers Sean.

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[boost.test] Floating point comparisons
by Anders Wang Kristensen 24 Nov '10

24 Nov '10

Hi, I'm using boost.test and BOOST_CHECK_CLOSE to verify that some matrices I compute are equal to some reference matices. This works fine as long as no entries are zero in either matrix (reference or computed). However, when an entry is zero, BOOST_CHECK_CLOSE always fails, which makes sense, since relative error is undefined in such cases. If either entry is zero, I can use BOOST_CHECK_SMALL instead with an absolute error: if (ref==0.0 || val==0.0) BOOST_CHECK_SMALL(ref - val, absolute_error); else BOOST_CHECK_CLOSE(ref, val, relative_error); But is this really the best way to do this? And if this is the standard way of doing this, shouldn't there be function in boost.test for automating this, like: BOOST_CHECK_NEAR(ref, value, relative_error, absolute_error); kinds regards, Anders (sorry if this post appears twice)

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