September 2005 - Boost-users

Matrix of submatricies...
by Edward Grace 15 Sep '05

15 Sep '05

Dear all, [you may need a fixed with font] Consider the following 4x4 matrix which is a 2x2 matrix of submatricies. A B | 0 0 C D | 0 0 ----+---- 0 0 | a b 0 0 | c d Clearly matrix operations such as products do not need to involve the off diagonal (zero) sub matricies. Is there a matrix type that "knows" about this type of matrix so that when prod() is carried out it does not do unnecessary operations with the zero elements? -ed

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[Regex] Empty regular expression
by Marco Craveiro 15 Sep '05

15 Sep '05

Hello boosters, First, apologies if this has been discussed before - I did some googling and could not find it. I've bumped into an interesting issue while using Boost.Regex. The documentation states: http://www.boost.org/libs/regex/doc/basic_regex.html Effects: Constructs an object of class basic_regex. The postconditions of this function are indicated in the table: Element Value empty() true size() 0 str() basic_string<charT>() Using 1.33, I get empty() set to false with the default constructor. In addition, if you attempt to search using an empty regex, the program segfaults. The following example demonstrates the problem: code: ------ #include <iostream> #include <string> #include <boost/regex.hpp> int main() { std::string line("this is an example line"); boost::smatch what; boost::regex re; std::cout << "re.empty(): " << re.empty() << std::endl; bool result = boost::regex_search(line, what, re); } output: ------ re.empty(): 0 Segmentation fault This does not happen if I initialize the regex using an empty string (it throws empty expression). Which leads to the main question (and the reason why I discovered all of this): is it possible to make a regular expression that matches anything? For instance, when using AWK, if you define a rule without a pattern, i.e.: { print $0; } I thought an empty regex would do the trick. Regards, Marco -- in software development, the design document is a source code listing. -- jack reeves

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Error compiling boost/tuple/tuple.hpp with boost 1.33 on VC 7.1
by Rob Caldecott 15 Sep '05

15 Sep '05

I have just upgraded to boost 1.33 from 1.32 and boost/tuple/tuple.hpp no longer compiles. I am using MS Visual Studio 2003 (7.1). Errors include: "boost-1_33\boost\tuple\detail\tuple_basic.hpp(66) : error C2332: 'class' : missing tag name" when compiling: template <class HT, class TT> struct cons; As I am new to boost, I have no idea how to continue. I am not even using tuple directly - it is included by iterator/indirect_iterator.hpp. Anyone else come across this? Looks like I'll have to switch back to 1.32. Thanks in advance.

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boost libraries under VxWorks
by swoh 15 Sep '05

15 Sep '05

Hello all. I am failing to compile the serialization library (from version 1.0.32) for use with VxWorks 5.4.2 (Tornado 2.2.1). I am restricted to their version of the g++2.96 compiler and matching libraries. I will probably be interested in using other boost libraries in the future (shared pointer at the least). The errors I am getting all have to do with default template parameters, although there may be other problems lurking ahead. Has anyone succeeded in using boost with this combination? Any tips? Thank you ori

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Boost.Iostreams + error handling
by Martin Slater 14 Sep '05

14 Sep '05

Hi there, Are exceptions the only way to propogate an error out of and IOStreams.Device policy? We have a lot of code using this style std::istream is(file); if(is) { .... } and would like not to have to change it all over to use ios exceptions but I can't see a way to avoid it. Is it possible? thanks Martin

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Re: [Boost-users] [filesystem] function to determine available space
by Sohail Somani 14 Sep '05

14 Sep '05

> -----Original Message----- > From: boost-users-bounces(a)lists.boost.org > [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Delfin Rojas > Sent: Wednesday, September 14, 2005 11:55 AM > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] [filesystem] function to determine > available space > > > > > I think the word "status" in space_status is misleading since > > > available/total space is not really a status. > > > > What makes you say that? > > > > Ben. > > > > It is just my interpretation of the word "status": the status > of a patient (stable, critical, etc.), the status of an > electronic device (powered, running, connected, disconnected, etc.). > > If I see a function or structure that is called > filesystem_status I would think it represents one or more > states in which the files system can be, like empty/full or > online/offline. I guess each possible total_size / used_size > combination is a possible filesystem status but still it > doesn't sound good to me. > > At the end of the day it is up to whoever implements the > function to decide, I was just giving my suggestion because I > think it is important programming constructs have a name from > which their usage/meaning can be easily guessed or deduced. Design by committee rocks.

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Re: [Boost-users] [statechart] Can events carry data?
by BRIDGES Dick 14 Sep '05

14 Sep '05

Sorry about the delay - got sidetracked by work. ;) Your clarifications were a great help. Many thanks for the library *AND* the help! Regards, Dick > -----Original Message----- > From: boost-users-bounces(a)lists.boost.org > [mailto:boost-users-bounces@lists.boost.org] On Behalf Of > Andreas Huber > Sent: Wednesday, August 31, 2005 2:57 PM > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] [statechart] Can events carry data? > > > BRIDGES Dick wrote: > > I'm still not clear on the requirements surrounding such an > > instance. For example, the reference requires that > > <code>new E(*pCE)</code> be well-formed and make "a copy of > > pE". > > Maybe I should have described that differently. That row in the table > translates as follows: > 1. event<> subtypes must have a publicly accessible copy constructor > (compiler-generated or not) > 2. If overloaded, operator new must be publicly accessible > > Since the library only requires the quoted expressions be > well-formed, > it is up to you to define the semantics of the copying. What the > copy-ctor actually does is of no concern to the library. > > > Does the current implementation work ok with > > boost::shared_ptr? > > I assume you mean shared_ptr<> instances as members of > events? I don't > see any problems here. > > > How about auto_ptr? > > That should work if you define a copy-ctor that transfers > ownership to > the copy. > > > If a data member > > would normally require a deep copy, would I be better off > > managing it external to the event object > > I'm not sure I understand the question. I don't see how you > would manage > that data-member externally; you don't mean a global > variable, do you? > Also, are we talking about a single-threaded or an MT system? > > > - or avoiding that > > type of data altogether? How many copies are we talking > > about here? > > Events that the user allocates with new are never copied. > Stack-allocated events are copied exactly once only if they are > deferred. See Step 8 here: > > http://boost-sandbox.sourceforge.net/libs/statechart/doc/refer ence.html#process_event > Any cautions and/or advise regarding the use of data members > in events would be appreciated. The library does not introduce problems that wouldn't exist otherwise. In an ST system everything should "just work" without you spending any thought on copying, other than that a reaction might be working with the original *or* the copy of the event. In an MT system the usual precautions against race-conditions, deadlocks, etc. apply. If it is too costly to deep-copy everything in the event, you must ensure that multiple threads accessing the shared part are appropriately locking mutexes, etc. HTH, -- Andreas Huber When replying by private email, please remove the words spam and trap from the address shown in the header. _______________________________________________ Boost-users mailing list Boost-users(a)lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

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Re: [Boost-users] Scons users?
by Thore Karlsen 14 Sep '05

14 Sep '05

On Tue, 13 Sep 2005 18:46:08 +0500, Alex Besogonov <cyberax(a)elewise.com> wrote: > >> On the Boost.Build list we were just discussing the fact that some > >> people otherwise inclined towards Boost have chosen Scons over > >> Boost.Build. It would be useful for us to understand some of the > >> reasons why, if some of you wouldn't mind letting us know. No flames, > >> please! >Well, SCons supports distributed building and binary repositories - >that's a MAJOR selling point. And Python is much nicer than jamfiles. > >PS: there's also mxx_ru (http://eao197.narod.ru/mxx_ru/) it's a build >system based on Ruby - it has some interesting features worth attention. >Unfortunately, its documentation is only in Russian, but this should not >be a problem for Vladimir Prus :) Another Python-based build system I like a lot is A-A-P (http://www.a-a-p.org) I haven't played much with SCons, but judging from the SCons documentation, A-A-P is a lot more powerful. I've found A-A-P to be indispensable for my builds, as well as other things like web page publishing. -- Be seeing you.

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locate a vertex by the index
by Giulio Veronesi 14 Sep '05

14 Sep '05

Hi, Excuse me for the very trivial question, but I'm new with boost and I'm looking for help. How I can locate a vertex of a graph by the index of the vertex? Thanks a lot in advance, Giulio

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boost libs dlls
by ned stoyanov 14 Sep '05

14 Sep '05

I am trying to introduce boost to my current company. I was wandering whether using boost requires linking against any libraries or is it all used like the STL simply by including header files. I've used some parts of boost before, which didn't require to link against anything but I want to make sure so I can package it up properly for other ppl to use. Cheers, Ned

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