September 2002 - Boost-users - lists.preview.boost.org

RE: [Boost-Users] Slightly Off-Topic, Books
by Jim.Hyslop 20 Sep '02

20 Sep '02

Your post is not "slightly" off topic, it is entirely off topic. -- Jim Hyslop moderator, boost-users(a)yahoogroups.com

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RE: [Boost-Users] Re: [BGL] Best way to abort an algorithm from w ithi n a visitor?
by Mark Storer 20 Sep '02

20 Sep '02

Using exceptions in this way just bugs me. Religious reasons I guess. As the Esteemed Mr. Hylsop ;) mentioned earlier, exceptions are for "oops". This seems alot like the whole "do{}while(0)" with various 'break' statements sprinkled in to avoid multiple returns/nested ifs. Useful, but Just Not Right. Your code has cooties! Nobody's going to want to sit next to it during recess... >So there's no way to affect feedback to the algorithm's dispatcher >without actually making modifications to the algorithm code. So modify away. Seems like a "breath_first_until" sort of thing would be quite useful. Pass in some sort of predicate, and away you go. I'm sure the community at large would be grateful. --Mark Storer Software Engineer Cardiff Software #include <disclaimer> typedef std::disclaimer<Cardiff> Discard; -----Original Message----- From: Chris Russell [mailto:cdr@encapsule.com] Sent: Wednesday, September 18, 2002 1:27 PM To: boost-users(a)yahoogroups.com Subject: [Boost-Users] Re: [BGL] Best way to abort an algorithm from withi n a visitor? > Now if you've got more than a hundred or so entries left to go, exceptions > really are the greener grass. > The size of the graph is not known a-priori (not at coding time anyway) but is likely to be quite large. > What's wrong with 'return', perhaps along-side some sort of 'done' status > variable? I'm only vaguely familiar with the visitor pattern, but these > would seem to be the obvious choice. > See my earlier reply. In this case I'm deriving my visitor from a base and overriding "event" handlers that receive their marching orders via const references and return void. So there's no way to affect feedback to the algorithm's dispatcher without actually making modifications to the algorithm code. "Mark Storer" <mstorer(a)cardiff.com> wrote in message news:E840F0B7E6189547BDB91DA8BF2228AB016255F8@csmail.cardiff.com... > If efficiency is your goal, exceptions are not the answer. Just enabling > exceptions at compile time makes a noticable performance hit. Actually > throwing an exception can gobble up a 1000 cycles, give or take. That's per > throw. If you catch and throw again, you'll pay again. > > Now if you've got more than a hundred or so entries left to go, exceptions > really are the greener grass. > > What's wrong with 'return', perhaps along-side some sort of 'done' status > variable? I'm only vaguely familiar with the vistor pattern, but these > would seem to be the obvious choice. > > --Mark Storer > Software Engineer > Cardiff Software > > #include <disclaimer> > typedef std::disclaimer<Cardiff> Discard; > Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

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Slightly Off-Topic, Books
by James Zappia 20 Sep '02

20 Sep '02

Hello, I'm a long time C/Perl programming and would like to transition into C++. What are some books I should pick up? I have the C++ Complete Reference for all the syntax sugar. I'm more interested in books that teach how to program in the mindset of objects. Also, books that don't read like RFCs ;) I learn better with examples and such -- not just brain dumps. Thank you in advance. Regards, James

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boost::shared_ptr confusion...
by someuserat 20 Sep '02

20 Sep '02

First, many thanks to Peter Dimov for answering my earlier questions. I've gotten hung up on something that may not be directly related to shared_ptr, but it's in the mix here. I suspect the real problem is my lack of experience using the STL algorithms, but I'm making an effort not to go back to writing my own loops with this project. Using my Widget theme, here's what I've got. A WidgetManager class contains a stl::list of shared_ptr<Widget> objects. It also contains a stl::vector of shared_ptr<WidgetMap> objects. WidgetMap objects contain a B+tree. (I know, I should probably change this to stl::map or multimap, I'll do that later) The index maps a data member of a Widget to a shared_ptr to the Widget for fast lookups. It is possible that new data members can be added or removed from the Widgets, and we have functions for handling that. Additional WidgetMap objects are added to the WidgetManager for Widget data members as needed. When adding a new WidgetMap, I need to loop through the existing set of Widgets and add them to the new WidgetMap. This is the simplest example I can think of as to what I'm trying to do, however obviously this does not work... void WidgetManager::addMap(const WidgetMapPtr i){ maps_.push_back(i); // have to write a function adapter here? for_each(widgetset_.begin(),widgetset_.end(),i->insert); } Along a similar line, when a Widget's data member collection is changed, I need to remove any WidgetMap objects fromm the WidgetManager that referenced the member being deleted. void WidgetManager::dropWidgetMember(const DataMemberPtr d){ // delete any maps using the target member // how to fix this bloody line? getIndexedMember returns a DataMemberPtr to the member it is keyed on. maps_.erase(remove_if(maps_.begin(),maps_.end(),(boost::mem_fn(&WidgetMap::getIndexedMember)).equals(d))); // get rid of the member itself members_.erase(remove_if(members_.begin(),members_.end(),boost::bind(&DataMember::equals,_1,d))); // rewrite the data file, we're all dirty anyway. this->compact(); } I feel like I understand what I want to do, but I cannot find a reference that explains how to do it the 'correct' way. At least not that I can grasp. Can someone point me in the right direction? Thanks, Mark

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Regex and Unicode
by Fr�d�ric Mayot 20 Sep '02

20 Sep '02

Hi, I'm trying to use Unicode with Regex in an MFC app. The preprocessor variable UNICODE is defined. But I obtain an error on the line : regex_search(sText, oResults, pRegExp); error C2665: none of the 4 overloads can convert parameter 1 from type 'class CString' sText is a CString which has a "const wchar_t*" operator. The problem is why doesn't the regex_search prototype require a "const wchar_t*" when UNICODE is defined ? Thanks. Fred (I read the documentation, but maybe I missed something...)

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BJam output directories on NT
by yg-boost-users＠m.gmane.org 20 Sep '02

20 Sep '02

Building my application using msvc-stlport. I've set ALL_LOCATE_TARGET=d:/src/pegdevbin/build. During processing, the paths get too deep for NT and eventually the mkdir fails and then of course the build stops. Anyway to shorten the deep paths that are automatically created or should I start chopping up allyourbase.jam? I won't be doing any build variants on a per platform basis so I don't need the deep paths that specify the various options in effect. Thanks for the help (and all the great work too...) Rob

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RE: [Boost-Users] Re: Borland C++ Builder 5.5 & scoped_ptr
by Mark Storer 19 Sep '02

19 Sep '02

>>Are you saying that if I switch from >> scoped_ptr to shared_ptr the destructor will get called? Is he saying that the destructor is NOT getting called with scoped_ptr? (!) --Mark Storer Software Engineer Cardiff Software #include <disclaimer> typedef std::disclaimer<Cardiff> Discard; -----Original Message----- From: Peter Dimov [mailto:pdimov@mmltd.net] Sent: Thursday, September 19, 2002 11:07 AM To: Boost-Users(a)yahoogroups.com Subject: Re: [Boost-Users] Re: Borland C++ Builder 5.5 & scoped_ptr From: "Brian" <bneal(a)zeus.ia.net> > --- In Boost-Users@y..., "Gennadiy E. Rozental" <rogeeff@m...> wrote: > > This was discussed during Boost.Test review. > > Peter some time ago made a changes in boost::shared_ptr that allows > > it to be used with Borland 5.5 namely in the situation you > described. > > > > Gennadiy. > > Hi...could you clarify this? All I noticed was that shared_ptr had > that compile time check for an incomplete type removed, whereas > scoped_ptr still has it. Are you saying that if I switch from > scoped_ptr to shared_ptr the destructor will get called? Yes, shared_ptr will call the destructor. It only requires a complete type at construction time. Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

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RE: [Boost-Users] Re: [BGL] Best way to abort an algorithm from w ithi n a visitor?
by Mark Storer 19 Sep '02

19 Sep '02

>Using the Boost library as it currently stands, >it appears the best way to abort the algorithm >is to throw an exception. Granted. I'd even go so far as to say "the only way" (based on my vast experience... I've actaully vistor's code once). >Whether or not throwing an exception is >acceptable from a general programming standpoint >is a topic more suited to a general C++ >discussion list Any recommendations? Preffereably something with an archive/FAQ so we don't drag up Holy War #42... --Mark Storer Software Engineer Cardiff Software #include <disclaimer> typedef std::disclaimer<Cardiff> Discard;

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RE: [Boost-Users] Re: [BGL] Best way to abort an algorithm from w ithi n a visitor?
by Jim.Hyslop 19 Sep '02

19 Sep '02

Mark Storer [mailto:mstorer@cardiff.com] wrote: > If Boost's source were a closed book, and the only option was > to throw an > exception, then so be it. But that is not the case. On that note, I'm going to bring this thread back to discussion of how to use the current Boost library. Using the Boost library as it currently stands, it appears the best way to abort the algorithm is to throw an exception. Whether or not throwing an exception is acceptable from a general programming standpoint is a topic more suited to a general C++ discussion list (if anyone decides to take it there, let me know - I'd like to follow it). Whether or not to add a return value to the BGL is a topic more suited to the main Boost mailing list. -- Jim

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RE: [Boost-Users] Re: [BGL] Best way to abort an algorithm from w ithi n a visitor?
by Mark Storer 19 Sep '02

19 Sep '02

In general, I agree that taking personal issue with the use of some language feature is a little silly. In specific, I'm going to disagree with you both for exceptions and the whole do{}while(0) thang. I'm sitting next to my copy of Stroustrup's "The C++ Programming language" (2nd edition). Chapter 9 covers exceptions. This chapter makes it clear that the purpose of exceptions is to handle errors: " The fundamental idea is that a function that finds a problem that it cannot cope with /throws/ an exception, hoping that its (direct or indirect) caller can handle the problem. " Same thing with the do{}while(0) construct. Using a loop as an error handler is quite similar. One could argue that a break is far more efficient than a throw. A counter-argument is that the throw carries a great deal more information about what went wrong. Once the excreta impacts the air-pusher-thingy, speed becomes a secondary concern (far more often than not). If you want to abort a function due to an error then throw an exception. If you want to return a value then do so. And while using a language feature for something other than its original intent is not criminal, there are usually 'proper' ways to do things already built into the language, ways that often work better than subjecting some poor unsuspecting feature to your vile, unnatural manipulations. <Dudly Do-Right>You fiend!</Dudly Do-Right> In the case that brought all this up (returning a value from a graph's visitor to avoid iterating through the whole graph) the proper way to handle it is to alter the algorithm to allow for early termination. If Boost's source were a closed book, and the only option was to throw an exception, then so be it. But that is not the case. So do it right... as Chris Russell (the original poster) has decided to do. --Mark Storer Software Engineer Cardiff Software #include <disclaimer> typedef std::disclaimer<Cardiff> Discard; -----Original Message----- From: Peter Dimov [mailto:pdimov@mmltd.net] Sent: Thursday, September 19, 2002 9:20 AM To: Boost-Users(a)yahoogroups.com Subject: Re: [Boost-Users] Re: [BGL] Best way to abort an algorithm from withi n a visitor? From: "Mark Storer" <mstorer(a)cardiff.com> > Using exceptions in this way just bugs me. Religious reasons I guess. As > the Esteemed Mr. Hylsop ;) mentioned earlier, exceptions are for "oops". > This seems alot like the whole "do{}while(0)" with various 'break' > statements sprinkled in to avoid multiple returns/nested ifs. Useful, but > Just Not Right. A common misconception. Many people try to project their own ideas/expectations on language features, rather than simply using them as tools where appropriate. There is nothing "oops"-y about exceptions. They are a control flow mechanism; one that has interesting properties, but a control flow mechanism nonetheless. If it works and leads to a better code, it's foolish to avoid it without a technical reason. A similar example is when people don't use "struct" for C++ classes because it "doesn't feel right", or when trying to choose between "typename" and "class" for template parameters. The language features simply do not carry this kind of religious/emotional payload. It's all in your mind. Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

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