March 2007 - Boost-users - lists.preview.boost.org

any boost iterator adapter to make it java style iterator ?
by abir basak 03 Mar '07

03 Mar '07

Hi, In some case I need a iterator which knows its position (index ) in the container, so that I can get the index back from iterator. The need is two fold. 1) This is needed for simultaneous traversal to different container. i.e i have vector<point> and vector<velocity> where each point corresponds to velocity at same position. Thus converting the iterator to the index helps. But even better if I have a multi iterator, which can club a set of iterators, and allow to return all of them (like (*it).point() returns point, (*it).velocity() returns velocity etc. Also it defines ++, -- etc the same way (i.e increments all these, or one in a logic , say next point is a jump in velocity by 2 etc), so that I can use boost::sub_range for these kind of iterator. 2) I need to convert iterator to index, as I need to store certain portion of a container (which changes its size) in a class. There I can only store index as iterator may get invalidated. It is something like, void mark_if_useful(point_sub_range r){///an portion of the container point_iterator it = r.begin(); for(; it != r.end() ; ++it){ if ((*it).x == 123 ) { ///ok certain criterion is fulfilled ///I need to mark (ans store tis position) ///I can't store *it as it is a pointer to a movable object ///However I can store (*it).index() may be it is 5th location in the vector, and (*it)>container() also the reference to the container ///may not be needed if the container is globally available. ///if some object also gets removed the the remove count from the container can be added to have a unique linear index (that can me done adding additional method to the container :) ) } } } -- Abir Basak, Member IEEE Software Engineer, Read Ink Technologies B. Tech, IIT Kharagpur email: abir(a)abirbasak.com homepage: www.abirbasak.com

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The future of boost::scope_guard
by Florin Trofin 03 Mar '07

03 Mar '07

Hi, I noticed that there is a scope_guard.hpp in the multi_index/detail folder. Are there any plans to make this very useful class part of the "official" library? Looking at the comments at the top there seem to be several TODOs. I also found this link: http://www.zete.org/people/jlehrer/scopeguard.html Florin.

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[filesystem] why no exceptions?
by n.torrey.pines 02 Mar '07

02 Mar '07

Wouldn't it make more sense for filesystem::ifstream in("invalid_file_name"); to throw an exception rather than treat the error in the old fashion?

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[Ann] Boost and Google Summer of Code 2007
by John Maddock 02 Mar '07

02 Mar '07

Dear Boosters, It is a pleasure to announce that Boost will be applying as a mentoring organization for the upcoming Google Summer of Code 2007. There is a lot of preparation work to be done and little time to do it. A page has been set up at the Boost Wiki: http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl?Google_Summe… which will hold a list of preliminary ideas for students to take up and use in their own applications to GSoC07. Please feel free to contribute by directly editing the Wiki page. Any questions, requests for feedback etc. can be conducted through the Boost lists. Remember that this initiative, as Boost itself, is the result of many individuals' contribution and ideas, which means we are looking forward to *your* feedback. Sincerely, John Maddock

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Boost on scratchbox
by Amy Sockanathan 02 Mar '07

02 Mar '07

I am trying to build bjam to install Boost and am getting the following error...... [COMPILE] bin.linuxx86.debug/yyacc "gcc" -o bin.linuxx86.debug/yyacc -DOPT_HEADER_CACHE_EXT -DOPT_GRAPH_DEBUG_EXT -DOPT_SEMAPHORE -DOPT_AT_FILES -DOPT_FIX_TARGET_VARIABLES_EXT -DOPT_IMPROVED_PATIENCE_EXT -DYYSTACKSIZE=5000 -pedantic -g -O0 -fno-inline -Wno-long-long yyacc.c ...failed [COMPILE] bin.linuxx86.debug/yyacc... [COMPILE] bin.linuxx86.debug/mkjambase "gcc" -o bin.linuxx86.debug/mkjambase -DOPT_HEADER_CACHE_EXT -DOPT_GRAPH_DEBUG_EXT -DOPT_SEMAPHORE -DOPT_AT_FILES -DOPT_FIX_TARGET_VARIABLES_EXT -DOPT_IMPROVED_PATIENCE_EXT -DYYSTACKSIZE=5000 -pedantic -g -O0 -fno-inline -Wno-long-long mkjambase.c ...failed [COMPILE] bin.linuxx86.debug/mkjambase... ...skipped jambase.c for lack of mkjambase... ...skipped bjam for lack of jambase.c... ...skipped jam for lack of bjam... ...failed updating 2 targets... ...skipped 3 targets. Any suggestion what I need to get this to complie. I am using scratchbox on an Ubuntu machine. Thanks - Amy

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[signals] per slot mutexes
by Frank Mori Hess 01 Mar '07

01 Mar '07

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I've got thread_safe_signals working with a single mutex per signal, which is only locked/unlocked once per signal invocation. However, it is causing problems with deletion_test.cpp. The deletion test checks if a slot is able to disconnect another slot which is ordered later in the same signal invocation. From the signals docs: "If a signal/slot connection is disconnected at any time during a signal's calling sequence, the calling sequence will still continue but will not invoke the disconnected slot." When the list of blocked slots is created at the beginning of signal invocation, before running any slots, then the signal invocation never notices that a later slot has been disconnected by an earlier slot. It seems to me the only solutions are to either keep per-slot locking, or to drop the requirement that the signal recognize changes to the connection status that happen while the invocation is in progress. I don't have a good feel for how important a feature this is. My inclination is to just keep per-slot locking. - -- Frank -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (GNU/Linux) iD8DBQFF5uiA5vihyNWuA4URAkWCAKCPm3xLEp6z1K8Nk5Vp8wHVNKkXqwCfZ7Il eL0Axnl/SD/4m6i3j54OnfA= =lSky -----END PGP SIGNATURE-----

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(no subject)
by gzahl＠arcor.de 01 Mar '07

01 Mar '07

Hi, > Hello Manuel, >> Hi, >> >> Im defining a class with a multi_index_container as base. >> When i construct a instance of this class, and the >> multi_index_container is called, the program crashes. It even >> crashes, when i dont use it as a base class. > [...] >> This compiles just fine, but if i run the code i get the >> following backtrace after a Sigmentation Abort. It happens, >> when the queue::queue() is called. Someone a idee whats it >> about? Im new to boost::multi_index, so maybe i misunderstud >> something? Thank you > > Well, what you're doing is AFAICS correct, so you shouldn't > be getting this crash. You haven't provided a complete > test program showing producing the crash, so I wrote one > myself after what you've shown and tried it locally, no > problems here. Could you please try the attached jung.cpp > file? Does it crash also? If it doesn't then there's more > to your program than you have described, maybe you can > send compilable program showing the issue. If jung.cpp > crashes, then could you please provide the following info? The Testprogramm jung.cpp does not crash on my machines (im testing on a ubuntu 6.10 and a debian 3.1 system, both working with g++ 4.0.2) I will try to get a example which reproduces my error, but in the meantime i was thinking about the libc stuff. Maybe this is the real problem thing? i changed to 4.0.2 from a 3.x version just some weeks ago, so maybe here is the problem, because some lib im using is not compiled with 4.0.2? is there a way i can get the compiler version a library was compiled with? > > 1. What system are you running this on? > 2. The stacktrace mentions a failed assertion in libc.so. Can > you see the source code that's causing the assertion? Maybe > it sheds some light. Im not sure about, where to see this sourcecode? scoped_lock(lightweight_mutex & m): m_(m.m_) { pthread_mutex_lock(&m_); } these are the lines alst mentioned in the backtrace "/usr/local/include/boost/detail/lwm_pthreads.hpp:72" from #5. But this is not what you meant, right? > 3. Can you try the attached lock.cpp file? Crash/no crash? > I didnt tried, because example worked fine. > Looking forward to your response, Thanks for help so far. I hope we can fix it soon. Ill go on, cut some working code out, which reproduces the error. > Joaquín M López Muñoz > Telefónica, Investigación y Desarrollo Manuel Jung Viel oder wenig? Schnell oder langsam? Unbegrenzt surfen + telefonieren ohne Zeit- und Volumenbegrenzung? DAS TOP ANGEBOT JETZT bei Arcor: günstig und schnell mit DSL - das All-Inclusive-Paket für clevere Doppel-Sparer, nur 44,85 inkl. DSL- und ISDN-Grundgebühr! http://www.arcor.de/rd/emf-dsl-2

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[signals] dropping ThreadingModel template parameter
by Frank Mori Hess 01 Mar '07

01 Mar '07

It seems that now that we drop locks before running slots, we can get by with using boost/detail/lightweight_mutex.hpp for our mutex. Since it is header-only, and apparently compiles to a null mutex if the compiler is in single-threaded mode, I don't see much need for a ThreadingModel template parameter on the signal class any more. I'm dropping it from thread_safe_signals. -- Frank

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[signals] scoped_blocker for connections?
by Frank Mori Hess 01 Mar '07

01 Mar '07

I wonder if it might be convenient to provide a scoped_blocker object that lets a connection be blocked/unblocked in an exception-safe way, similar to how a scoped_lock locks a mutex, or a scoped_ptr owns allocated memory. A fancier scheme would be to provide a shared_blocker, where when you request a shared_block from the connection it does reference counting so the connection remains blocked until the last shared_blocker (requested by any connection handle object referring to the same connection body) goes out of scope. This could be implemented with a shared_ptr that has a custom deleter, and a weak_ptr kept in the connection body to allow different connection handles to get copies of the same shared_ptr. -- Frank

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boost::variant question
by Digvijoy Chatterjee 01 Mar '07

01 Mar '07

Hi, i have a boost::variant holding some C++ types which have to be inserted into the database : boost::variant<int, std::string, double > dbColumnValueVar; before i insert the value_type into the database I need to call a processing function which is overloaded for every datatype used in the variant ie. each of these functions are defined process ( int ); process ( std::string ); process ( double); template <class T> process(T); ..... what i do not understand is how do i use apply_visitor or some other tactic to automatically dispatch the call to the right process function as in : boost::variant<int, std::string, double > dbColumnVar; dbColumnVar = "hello world"; process ( dbColumnVar ); // should call process std::string ....but is always calling the generic template version ?? dbColumnVar = 1.3434; process ( dbColumnVar ); //again calls generic template not specialization cout << dbColumnVar is somehow able to get the correct overloaded << operator for the hidden datatype irrespective of datatype ?? Any help will be appreciated Thanks Digz

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