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is_base_and_derived broken in 1.30.0?
by Jeff Muller 15 May '03

15 May '03

Originally posted this on 5/6, but it never showed up. Here goes again... Hi, The following code: const bool isWS = ::boost::is_base_and_derived<std::wstring,std::wstring>::value; sets isWS false with VS.NET 2003 (_MSC_VER=1310) in version 1.30.0 of the libraries. It is correct with version 1.27.0. Thanks, Jeff

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Using the Python interpreter
by dima_mouromtsev 15 May '03

15 May '03

Hello All! I've the problem with the next code: class MyWindow { ... MyWindow() {} ~MyWindow() {} MyOperation() { Py_Initialize(); handle<> main_module(borrowed(PyImport_AddModule("__main__"))); handle<> namespace(borrowed(PyModule_GetDict(main_module.get()))); try { handle<>(PyRun_String("hello = file('c:\\hello.txt', 'w')\n" "hello.write('Hello world!')\n" "hello.close()", Py_file_input, namespace.get(), namespace.get())); } catch(error_already_set) { ... } Py_Finalize(); } }; When I start this code, that's all right. If I move Py_Finalize() to destructor, the program work, but when I close the program an exeption rise (Py_FatalError("UNREF invalid object")). Next, I exclude Boost classes: ... MyOperation() { PyObject* dict = PyModule_GetDict(PyImport_AddModule("__main__")); PyRun_String("hello = file('c:\\hello.txt', 'w')\n" "hello.write('Hello world!')\n" "hello.close()", Py_file_input, dict, dict); } So the program work well and there is no exeptions at exit. What is my problem? How can I use Boost in right way? Please Help Thanks Dima

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shared_from_this from a destructor
by ostware 15 May '03

15 May '03

(This message is also posted on sourceforge. Please forgive the double posting, but I am still unfamiliar with the community...) version: boost 1.30.0 library: smart pointers I am using the boost::enable_shared_from_this base class from the smart pointer library to implement shared_from_this in my classes. I was amazed to find this class, after hours of thashing trying even to figure out the very problem it solves. So, first off, thanks to the boosters. My problem is that shared_from_this() throws boost::bad_weak_ptr if called from my class's destructor. Is this a design decision? a bug? am I misreading a class requirement? The problem (if it is one...) is that sp_counted_base::release() decrements use_count_ before calling dispose(). Then when my class calls shared_from_this from its destructor (via dispose()), sp_counted_base::add_ref fails (use_count == 0) and throws boost::bad_weak_ptr. I would suggest either setting use_count_ after dispose(), or clarifying in the docs that shared_from_this can't be called from a destructor. (... which would send me back to the drawing board to solve my problem) It would also be handy to have an exception less version of share_from_this which justs returns a null shared_ptr. Thanks for any help. ... Michael Ost Something like this (warning: uncompiled, untested!) ... class T : public enable_shared_from_this { public: T() {} ~T() { shared_ptr<T> ptr = shared_from_this(); // trouble: exception, can't get a shared_ptr } }; main() { shared_ptr<T> ptr = shared_ptr(new T()); ptr.reset(); }

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? Using std::max_element() on a multi_array
by Neil Mackie 15 May '03

15 May '03

I'm looking for advice on using std::max_element() with boost::multi_array. When passing a multi_array to max_element() I was expecting to get an iterator referring to the largest element in return. However my compiler tells me the iterator refers to a sub_array<class RAClass::RAPoint,1> instead, and I don't know why or what to do about it. Its clear that inexperience with multi_array and max_element() is the cause. Is anyone able to shed some light on the subject? Details: ―--- .h file ―--- namespace RAClass { typedef boost::multi_array<RAPoint,2> CELL_TABLE; CELL_TABLE* m_cells; ―--- .cpp file ―--- CELL_TABLE::iterator e = std::max_element(m_cells->begin(),m_cells->end(), RAPoint::lower); // RAPoint::lower() compares two RAPoints int height = e->getHeight(); ―--- compiler output ―--- getHeight' : is not a member of 'sub_array<class RAClass::RAPoint,1>' TIA Neil (J Mackie). By the end of this year the Radiocommunications Agency and all responsibility for regulating the radio spectrum and communications services will become part of Ofcom - the new converged regulator for the communications sector. See the Ofcom transitional website at www.Ofcom.org.uk for more details.

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BGL - misc problems encountered
by Chuck Messenger 14 May '03

14 May '03

I've been testing out the BGL, and have found some small problems. Is this a good forum to post these? If not, please set me straight. I have in mind to post more of these -- in the interest of helping iron out the library. Maybe the developer list would be more appropriate? Or a BGL-specific list, if one exists...? Problem 1: In the documentation, under "Using adjacency_list", subsection "Custom Edge Properties", it shows a method for declaring a custom property tag: > struct flow_t { > typedef edge_property_tag kind; > }; > > struct capacity_t { > typedef edge_property_tag kind; > }; It goes on to say that an alternative method is this: > enum edge_myflow_t { edge_myflow }; > enum edge_mycapacity_t { edge_mycapacity }; > > namespace boost { > BOOST_INSTALL_PROPERTY(edge, myflow); > BOOST_INSTALL_PROPERTY(edge, mycapacity); > } In the rest of the code included in the documentation, it uses the first method. Finally, it says: > The file edge_property.cpp shows the complete source code for this example. However, the code in edge_property.cpp is completely different -- using the second method rather than the first. So, at a minimum, the final sentence is wrong. I suggest the alternative methods should both be shown in the sample code. I made the necessary changes to edge_property.cpp -- here's the diff (against Boost release 1.30.0): 78a79,88 > #define ALTERNATE // comment this out to see an alternate method > > #ifdef ALTERNATE > struct flow_t { > typedef edge_property_tag kind; > }; > struct capacity_t { > typedef edge_property_tag kind; > }; > #else 86c96 < --- > #endif 95c105,109 < property_map<Graph, edge_mycapacity_t>::const_type --- > #ifdef ALTERNATE > typename property_map<Graph, capacity_t>::const_type capacity = get(capacity_t(), G); > typename property_map<Graph, flow_t>::const_type flow = get(flow_t(), G); > #else > typename property_map<Graph, edge_mycapacity_t>::const_type 97c111 < property_map<Graph, edge_myflow_t>::const_type --- > typename property_map<Graph, edge_myflow_t>::const_type 98a113 > #endif 125a141,145 > #ifdef ALTERNATE > typedef property<capacity_t, int> Cap; > typedef property<flow_t, int, Cap> Flow; > typedef adjacency_list<vecS, vecS, bidirectionalS, no_property, Flow> Graph; > #else 129a150 > #endif 163a185,188 > #ifdef ALTERNATE > property_map<Graph, flow_t>::type > flow = get(flow_t(), G); > #else 165a191 > #endif Problem 2: edge_proprety.cpp, as included in Boost release 1.30.0, generates warnings under gcc 3.2.2, since it is missing a couple of typenames. Here's the needed patch: 95c95 < property_map<Graph, edge_mycapacity_t>::const_type --- > typename property_map<Graph, edge_mycapacity_t>::const_type 97c97 < property_map<Graph, edge_myflow_t>::const_type --- > typename property_map<Graph, edge_myflow_t>::const_type - Chuck

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RE: [Boost-Users] Re: find_if and calling a member function
by Tom Matelich 14 May '03

14 May '03

> From: Russell Hind [mailto:yg-boost-users@gmane.org] > > Tom Matelich wrote: > > > > 1) write your own algorithm find_if_equal, then you only > need one bind (~10 > > lines of code separate from your call) > > This is what I was looking for, and I was really wondering (although > didn't say it) if there were such a thing in boost already. > I haven't > found one, but there are quite a few bits of boost I'm not > familiar with > yet. > I don't think boost has any extra general algorithms laying around, unless they're hiding in the details directories. ----------------------------------------------------------------------- DISCLAIMER: Information contained in this message and/or attachment(s) may contain confidential information of Zetec, Inc. If you have received this transmission in error, please notify the sender by return email. -----------------------------------------------------------------------

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Question regarding boolalpha and lexical_cast for 1.30.0
by Paul Wendt 14 May '03

14 May '03

Hello, I'm trying to get lexical_cast to convert a std::string to bool; I realize that this is done with normal IOStreams by using boolalpha. Is there a way to do this with lexical_cast? I saw some old posts in the archives and they were apparently with older code bases because I was unable to get their code snippets to work properly [either that or my compiler is messed up :)]. For reference, I use Visual Studio .NET 2002. Thank you very much for any assistance in advance. --Paul

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RE: [Boost-Users] indentation vs. braces
by Ben Hutchings 14 May '03

14 May '03

Ryan Barrett <rbarrett(a)stanford.edu> wrote: <snip> > incidentally - and this is *way* off-topic - python's control flow is > defined by indentation. iirc, it works just like you'd want. > > however, i should offer the disclaimer that that's pretty much all i > know about python, other than the fact that ESR likes it: <snip> Some people would consider the ESR association a flaw, but that's going way off-topic. However, I do know about Python and would recommend pretty much all programmers to have a look at it.

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RE: [Boost-Users] find_if and calling a member function
by Tom Matelich 14 May '03

14 May '03

Define easier :) Not to be picky, but how little do you expect to have to type? 1) write your own algorithm find_if_equal, then you only need one bind (~10 lines of code separate from your call) 2) write a functor, ObjectNameCompare (less than 15 lines of code separate from your call) > -----Original Message----- > From: Russell Hind [mailto:yg-boost-users@gmane.org] > Sent: Tuesday, May 13, 2003 9:31 AM > To: boost-users(a)yahoogroups.com > Subject: [Boost-Users] find_if and calling a member function > > > 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 > > > > ------------------------ Yahoo! Groups Sponsor > ---------------------~--> > Rent DVDs Online - Over 14,500 titles. > No Late Fees & Free Shipping. > Try Netflix for FREE! > http://us.click.yahoo.com/YoVfrB/XP.FAA/uetFAA/EbFolB/TM > -------------------------------------------------------------- > -------~-> > > 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/ > > ----------------------------------------------------------------------- DISCLAIMER: Information contained in this message and/or attachment(s) may contain confidential information of Zetec, Inc. If you have received this transmission in error, please notify the sender by return email. -----------------------------------------------------------------------

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Test message from moderator
by Jim.Hyslop 13 May '03

13 May '03

My apologies for the noise, I'm trying to resolve some problems experienced by some users of this list. -- Jim Hyslop Moderator, Boost-users(a)yahoogroups.com

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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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Help using Boost Graph Library with C++Builder 6
by asterixthegaul2003 09 May '03

09 May '03

Hi, Has anyone successfully used to Boost Graph Library (BGL) with C++Builder 6? I'm getting compilation errors. Here's what I've done: I downloaded the latest Boost (1.30.0) from boost.org and installed it. I then tried to compile the quick-tour.cpp file using the mingw compiler - no problem. I then tried to compile using the C++Builder IDE and I get the following compile errors: [C++ Error] tuple_basic.hpp(158): E2238 Multiple declaration for 'element<N,T>' [C++ Error] tuple_basic.hpp(143): E2344 Earlier declaration of 'element<N,T>' I also tried using the command line compiler (bcc32.exe - version 5.6), but get the same errors (and more). Can someone tell me what I'm doing wrong? Do I need to do something special to prepare the boost libraries for use with Borland (e.g., using the Boost Jam stuff)? Some of the documentation said I should only have to set the include path. This seemed to work with mingw. Thanks, Craig

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RE: [Boost-Users] Re: Why isn't the "last access time" part of the filesystem library?
by Ben Hutchings 09 May '03

09 May '03

richard_fanta <richard.fanta(a)morganstanley.com>: > --- In Boost-Users(a)yahoogroups.com, "Ben Hutchings" > <ben.hutchings@b...> wrote: > > richard_fanta <richard.fanta@m...> wrote: > > > Beman Dawes <bdawes@a...> wrote: > > > > At 01:02 AM 5/6/2003, richard_fanta wrote: > > > > >Looking at the filesystem library and the attributes work in > > > > >boost-sandbox, I don't immediately see "last access time" > > > > >being available for a file or directory. > > > > > > > > > >"Last access time" was included in Dietmar Kuehl's original > > > > >dir_it. > > > > > > > > > >Can someone kindly tell me why this was removed? It's highly > > > > >useful, and part of every filesystem that I've seen. <snip> > > > > Perhaps we should do more to support attribute query within the > > > > main library, but I don't really think we should include any > > > > that aren't reliably supported by at least POSIX, Windows, and > > > > ISO-9660 systems. > > > > > > Your point is well made. However, it does seem odd that a > > > feature that is useful for >95% of all typical usage shouldn't be > > > in the library. > > > > What does that figure refer to, if anything? > > Typical application usage. Yes, mileage can vary. > > Out of the last 50 apps you wrote that did file access, how many > involved CD-ROMS/DVDs that were ISO 9660 filesystems? I think most of them could quite happily have worked with files on CD-ROMs, but then I tend to write general-purpose code rather than very specific applications. A few of them needed to know file modification times. <snip> > > and updates to them may be disabled because the volume is read- > > only (whether or not the underlying medium is read-only) or > > purely to avoid the cost of updating them. > > Even if the volume is read-only from one machine, it might still > help to know when the file was last altered. > > > Note that Windows NT maintains > > access times at quite a low resolution, to reduce this cost. > > Low resolution or not, it's there. When the file changes, the > timestamp is updated. That's information that many applications > would find useful. <snip> What you're talking about is the modification time, not the access time. I agree that *that* is useful and widely supported, but it's not what you were originally asking for!

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combinations of boost::condition
by Joshua Napoli 09 May '03

09 May '03

Is there any way to wait for one of several condition objects to become ready? Is there some reason that this capability is omitted from the thread library? I would like to do something like this: mutex monitorA, monitorB; condition conditionA, conditionB; double_condition conditionAB(conditionA,conditionB); void executeNextEvent() { lock lkA(monitorA); lock lkB(monitorB); //Wait for either conditionA or conditionB to become ready. conditionAB.wait(lkA,predicateA,lkB,predicateB); if(predicateA()) { executeEventA(); } else { executeEventB(); } } [Non-text portions of this message have been removed]

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RE: [Boost-Users] Re: Why isn't the "last access time" part of the filesystem library?
by Ben Hutchings 09 May '03

09 May '03

richard_fanta <richard.fanta(a)morganstanley.com> wrote: > Beman Dawes <bdawes@a...> wrote: > > At 01:02 AM 5/6/2003, richard_fanta wrote: > > > > >Looking at the filesystem library and the attributes work in boost- > > >sandbox, I don't immediately see "last access time" being available > > >for a file or directory. > > > > > >"Last access time" was included in Dietmar Kuehl's original dir_it. > > > > > >Can someone kindly tell me why this was removed? It's highly useful, > > >and part of every filesystem that I've seen. > > > > ISO/IEC 9660:1999 filesystems don't supply a "last access" time stamp, > > perhaps because the original uses were on write-once media. > > Which filesystems adhere to this spec other than CD-ROMs? Many DVDs use this too, but for most purposes they're basically just higher-capacity CDs. > > Perhaps we should do more to support attribute query within the main > > library, but I don't really think we should include any that aren't > > reliably supported by at least POSIX, Windows, and ISO-9660 systems. > > Your point is well made. However, it does seem odd that a feature > that is useful for >95% of all typical usage shouldn't be in the > library. What does that figure refer to, if anything? > Other options: > -For ISO 9660 filesystems, use the time created as the "last > access" time stamp. > -Throw a "FeatureNotSupportedException" or somesuch. Then the feature won't be at all portable, and might as well not be supported at all. Access times are far from a universal OS feature, and updates to them may be disabled because the volume is read-only (whether or not the underlying medium is read-only) or purely to avoid the cost of updating them. Note that Windows NT maintains access times at quite a low resolution, to reduce this cost.

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RE: [Boost-Users] call_traits and MSVC 7.1
by Randy Bowen 08 May '03

08 May '03

Thanks for the info. This is illegal code. That it compiled in MSVC 7.0 was a bug. The template parameter '_Source' can not be deduced from the callsite of doSomething. 14.8.2.4 in the ISO/IEC 14882 lists the forms in which template parameters can be deduced, but a qualified name involving nested types is not one of them. I suspect it's because of something like this: [Non-text portions of this message have been removed]

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