May 2003 - Boost-users - lists.preview.boost.org

Inconsistent regexp matching when using quantifiers?
by Dean 13 May '03

13 May '03

Hi all, I'm using regexp from boost-1.28 and experience the following behavior. Consider the following (somewhat artificial) regexp pattern: a{1}b As I expected, that pattern is found in "ab" but not "aab". To my suprise however, the same pattern *is* found in "aaab", "aaaaab", and any other string consisting of an odd number of "a"s followed by a "b". It is not found in strings consisting of an even number of "a"s followed by a "b". This seems odd (no pun intended). I see the same sort of behavior with quantifiers other than "{1}" and where the quantified expression matches other single characters. (Oddly enough, the behavior changes when using a quantified expression that matches multiple characters. "(ab){1}c" is found in "abc", "ababc", "abababc", and any other string containing "abc".) FWIW, I first observed the behavior when trying to find social security numbers with the following pattern: \d{3}-\d{2}-\d{4} As expected, that pattern was found in "123-12-1234" but not in "1234- 12-1234". However it *was* found in "1234567-12-1234". Is this behavior by design or is it a bug? If it's a bug, has it been fixed in a subsequent boost release? Also what is the correct behavior? Should "a{1}b" be found in "aab" (albeit starting at the second character)? FWIW, it's easy enough for me to workaround the current behavior with a pattern like this: (^|[^a])a{1}b Thanks, --Dean

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find_if and calling a member function
by Russell Hind 13 May '03

13 May '03

I have an object that has a member get_name which returns a string. I have a collection of these objects and would like to find one with a particular name. I am currently using find_if, equal and bind find_if(objects.begin(), objects.end(), bind(equal_to<string>(), name, bind(&object::get_name, _1))); Given Lambda doesn't compile under BCB6, is there an easier way to do this rather than having to make up 2 bind statements? Thanks Russell

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RE: [Boost-Users] boost::thread IDs
by Ben Hutchings 13 May '03

13 May '03

Mark Sizer wrote: > I know there was a discussion about the need for these and why > they're not in the library. I can't find it, however. > > I'm having the same problem the original poster had: I'm using > the thread ID as an identifier in a data structure (std::map in > this case). You can do that with Windows thread IDs, because they are simple integers. Unfortunately the Posix thread ID type (pthread_t) is an abstract data type and the only relation defined on it is equality (pthread_equal()). Some implementations use a type that can safely and correctly be compared with std::less, but there's no guarantee of that, so Boost can't offer such a guarantee either. > Now that I'm converting to the Boost threads library, I have to > change that. I'm not sure what to do instead. > > Any help, either a pointer to the original discussion or direct > suggestions, will be much appreciated. How about using pointers to boost::thread objects as IDs (they must of course be the instances used to start the thread, rather than instances created with the default constructor). Store each thread's own pointer in TLS (or TSS as Boost.Threads calls it). (This is tricky, though - you can't pass a thread's own ID to its initial function, as threads start to run immediately. I suppose you could use placement new, but that's a bit gross.) What's the need for thread IDs, anyway? Are you using a thread pool?

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boost::thread IDs
by Mark Sizer 13 May '03

13 May '03

I know there was a discussion about the need for these and why they're not in the library. I can't find it, however. I'm having the same problem the original poster had: I'm using the thread ID as an identifier in a data structure (std::map in this case). Now that I'm converting to the Boost threads library, I have to change that. I'm not sure what to do instead. Any help, either a pointer to the original discussion or direct suggestions, will be much appreciated. Thanks, - Mark P.S. Other than this glitch, my ObjectSpace Toolkit removal has been painless. Great libraries!

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scope of locked variables
by Peter G 12 May '03

12 May '03

hi there... what is the scope of locked variables? assuming that i declare a mutex in say a class scope.. and then lock it in some inner scope - say in a function.. what variables get locked? is it all the variables which are in the scope of the declaration (ie all the variables which are declared in the class)? or is it only the ones which are being used in that particular function (so that perhaps another thread could use the rest at "the same time")? for example: class Class1 { public: Class1::Class1(); ~Class1::Class1(); void f(int new) { boost::mutex::scoped_lock scoped_lock(mutex_outer) ; var1 = new; } void g(int new) { boos::mutex mutex_inner; boost::mutex::scoped_lock scoped_lock(mutex_inner) ; var1 = new; } private: boost::mutex mutex_outer; Class2 some_member_object; int var1; int var2; }; what gets locked when f() is called? when should i use g()? how do I go about just locking say var1 but NOT var2? if i lock the mutex in this class scope, does that mean that all the variables in some_member_object are locked as well? also, should i set up locks anytime i am using an object which might be accesses by another thread (even if I am just reading it) or is it enough to only lock variables when i am changing them? i know that's a lot of questions, but any help would be greatly appreciated. cheers peter

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[uBLAS] binary operation of vector and matrix with different type
by Zhang Le 12 May '03

12 May '03

hi, the following code generates a compile error raising from a macro in /ublas/traits.hpp: BOOST_STATIC_ASSERT ((boost::is_same<T1, T2>::value)); Because I'm trying to prod on a vector of size_t and a matrix of unsigned char. Because I want to save memory (the matrix is really huge) and I know the value in m will never exceed 255. The expression is ok to me (of course the result value is size_t). But the ASSERT prevent me from doing this. Is there a workaround that permits me doing this kind of case without sacrificing the memory efficiency? Using size_t in the matrix will use three times more memory. ublas::vector<size_t> v1(5); matrix<unsigned char> m(5,5); prod(m,v1); the same problem arises when I do prod(m,v2); here v2 is a vector<double> -- Sincerely yours, Zhang Le

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Re: (Spirit) Semantic Actions with member functions?
by Slava Akhmechet 12 May '03

12 May '03

I was able to get boost::bind working to bind the semantic action to the member function of MyGrammar. This seems like a superior solution. In any case, I am not sure how to pass custom data to a functor. When specifing a semantic action I have to pass the type of the functor, which implies that spirit creates a temporary object. Am I missing something? > Its time to switch your global function "myaction" into a functor. > Functors are classes that have a function call operator with the same > synopsis as your function. > The advantage is that one can pass custom data to it via a non-default > constructor. > > Functors should be and sometimes must be stateless, so care must be > employeed to use references in member data. > > Slava Akhmechet wrote: > > > I am playing around with Spirit and I seem to run into an architecture > > problem with semantic actions. Here's a small example. > > > > class MyGrammar : public grammar<MyGrammar> > > { > > public: > > template <typename ScannerT> > > struct definition > > { > > definition(MyGrammar const& self) > > { > > TestRule = str_p("test")[&my_action]; > > } > > > > rule<ScannerT> const& > > start() const { return TestRulet; }; > > > > private: > > rule<ScannerT> TestRule; > > }; > > }; > > > > My major problem is related to the fact that I cannot pass any custom > > data to my_action function. Since my_action is a global function, it > > has no knowledge of MyGrammar and must rely on global variables. > > Ideally, I would pass self to my_action to be able to hold state. What > > is a general way to get around this problem? The documention mentions > > a way to specify member functions as semantic action actors using > > boost's bind facilities but I was unable to get it to work. > > Thanks in advance. > > > > P.S. Sorry for a fairly newbie question, I was unable to find the > > answer online or in the docs. > > P.P.S. I might have accidently double posted this. Sorry about that. > > > > > > > > *Yahoo! Groups Sponsor* > > > > <http://rd.yahoo.com/M=247865.3269369.4566997.1261774/D=egroupweb/S=17050067…> > > > > > > > > Info: <http://www.boost.org> > > Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> > > Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> [mailto:boost-users-unsubscribe@yahoogroups.com>] > > > > > > Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service > > <http://docs.yahoo.com/info/terms/>. > > > > > Info: <http://www.boost.org> > Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> > Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> [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: Why isn't the "last access time" part of the filesystem library?
by Ben Hutchings 11 May '03

11 May '03

Beman Dawes wrote: > At 06:13 AM 5/8/2003, Peter Dimov wrote: <snip> > >This is a misunderstanding. Last access time (struct > >stat::st_atime) and creation time (st_ctime) aren't universal. Unix's ctime is actually change time, not creation time - it is the time when certain metadata were last changed. > >Modification time (st_mtime) is common, except on read-only > >filesystems, which typically only have ctime. > > > >Judging by your "last altered" remark, you mean mtime but call > >it "last access." > > > >I think that it would be entirely reasonable (and very useful - > >can avoid reading a file if it hasn't changed since last read) > >to provide mtime. On read-only filesystems, the creation time > >should be returned. You're mixing the concepts of filesystem API and the filesystem on disk. Normally the same filesystem API can be used for any file- system supported by the OS, and file times on an inherently read- only filesystem can appear as modification time and (if the OS supports the notion) as creation or change time. > Yes, I had a similar thought. > > What format should be used to report the mtime? I'd prefer to > keep the coupling to other Boost libraries low, so I guess that > would mean just using std::time_t. That also has the advantage > of not promising higher resolution than can actually be > delivered by most platforms. Seems reasonable to me. > What to do if the filesystem doesn't attach any time at all to > a file? Fail at compile time? Always return some date in the > past, like January 1, 1900, that is impossible as a real mdate > (since computers were not invented yet) and so can be relied > upon to indicate "no date available"? Use std::time_t(-1) to be consistent with std::time and std::mktime.

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MSVC 6.0 and BOOST_HAS_PARTIAL_STD_ALLOCATOR
by Joaquín Mª López Muñoz 10 May '03

10 May '03

Shouldn't BOOST_HAS_PARTIAL_STD_ALLOCATOR be defined for MSVC 6.0? Seems it is not. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

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(Spirit) Semantic Actions with member functions?
by Slava Akhmechet 09 May '03

09 May '03

I am playing around with Spirit and I seem to run into an architecture problem with semantic actions. Here's a small example. class MyGrammar : public grammar<MyGrammar> { public: template <typename ScannerT> struct definition { definition(MyGrammar const& self) { TestRule = str_p("test")[&my_action]; } rule<ScannerT> const& start() const { return TestRulet; }; private: rule<ScannerT> TestRule; }; }; My major problem is related to the fact that I cannot pass any custom data to my_action function. Since my_action is a global function, it has no knowledge of MyGrammar and must rely on global variables. Ideally, I would pass self to my_action to be able to hold state. What is a general way to get around this problem? The documention mentions a way to specify member functions as semantic action actors using boost's bind facilities but I was unable to get it to work. Thanks in advance. P.S. Sorry for a fairly newbie question, I was unable to find the answer online or in the docs. P.P.S. I might have accidently double posted this. Sorry about that.

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