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Rationale for intrusive_ptr?
by Brian Neal 01 Feb '05

01 Feb '05

Hi, I need some help understanding when and why you would want to use intrusive_ptr. Does someone have an example? I didn't get much out of the current documentation for it. Thank you. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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Two issues with lexical_cast
by Yuval Ronen 01 Feb '05

01 Feb '05

Hi. I'm probably just another one out of a million who make these remarks, but I found nothing in the documentation about them, so I'll mention them anyway. 1. lexical_cast(Source arg) takes the source argument by value. Why not by const& ? Calling lexical_cast(some_basic_string) now makes a copy of the source argument for no reason. 2. lexical_cast ignores trailing whitespaces, but not leading whitespaces. Meaning that int a = lexical_cast<int>("3 "); // three-space will work and return 3, but int a = lexical_cast<int>(" 3"); // space-three will throw. Why? There's no rationale here. Both cases should be treated in the same manner, and IMHO, that manner should be throwing. After a look at the code, it seems that the trailing-whitespace-ignore code ('stream >> std::ws' in line 151) was specifically added, so there was supposed to be a reason for this. But as I said, I believe this is wrong, at least as the default behaviour when converting a string to something else. Maybe some policies (IgnoreLeadingWhitespace, IgnoreTrailingWhitespace) can be added to control this? And again, I suppose I'm not the first to think of it... Thanks, Yuval

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RE: [Boost-users] Rationale for intrusive_ptr?
by Nat Goodspeed 01 Feb '05

01 Feb '05

> -----Original Message----- > From: boost-users-bounces(a)lists.boost.org [mailto:boost-users- > bounces(a)lists.boost.org] On Behalf Of Brian Neal > Sent: Monday, January 31, 2005 7:34 PM > To: boost-users(a)lists.boost.org > Subject: [Boost-users] Rationale for intrusive_ptr? > > Hi, I need some help understanding when and why you > would want to use intrusive_ptr. Does someone have an > example? I didn't get much out of the current > documentation for it. Thank you. [Nat] Consider: class MyClass; void some_func(const boost::shared_ptr<MyClass>& ptr); class MyClass { public: void process() { // BAD THINGS HAPPEN! some_func(boost::shared_ptr<MyClass>(this)); } }; In our current project, we've been bitten more than once :-( by situations that are analogous but less obvious. Inside a member function, you don't have a shared_ptr<MyClass>, you only have a dumb MyClass* 'this' pointer. But if MyClass is managed with smart pointers, you probably have processing functions that accept only a smart pointer to MyClass. A natural-looking data conversion is easy to code and makes the compiler happy. What happens, though, is that when you instantiate a new shared_ptr<MyClass> from your dumb 'this' pointer, it gets a whole new refcount object! In the example above, the temporary shared_ptr<> goes away as you're about to exit MyClass::process() -- which makes its spurious refcount go to 0 -- which deletes the MyClass instance in question, even though there are probably still existing shared_ptr<MyClass> references to the same instance lying around! (e.g. the one with which you called the process() method) We now use intrusive_ptr almost exclusively (vs. shared_ptr). We limit its intrusiveness by deriving all subject classes from an intrusive_base we wrote, which contains the refcount we use and a couple of methods. This practice has cut down considerably on bizarre crashes.

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implicitly_convertible<a,b>
by Benjamin Schmeling 31 Jan '05

31 Jan '05

Hi, I have exposed a bigint class which has no constructor for long_ . I added an additional constructor by defining .def("__init__", make_constructor(bigint_constructor)) This works fine. Now I want to use the implicitly_convertible function which expects from the class to have an constructor which takes the first argumen (in this case a long_) I used implicitly_convertible<boost::python::long_ ,bigint> but now the problem is that the original c++ class has no such constructor, but the wrapped class. How can I make him use my new constructor in implicitly_convertible? Benjamin

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Compile problems with multi_index on CW 9.3 (mac)?
by Marshall Clow 31 Jan '05

31 Jan '05

I'm trying to use boost::multi_index for the first time, and I'm getting odd compile errors. I have a class with two "keys", a text one and a numeric one, and I want to have two indices into the collection. So, I tried several things, and all of them get the same error: 'index_class' is not a member of class 'boost::multi_index::ordered_unique<boost::multi_index::identity<Foo>, boost::multi_index::detail::null_arg, boost::multi_index::detail::null_arg>' (and then an amazing cascade after that) Here's the basic idea: typedef boost::multi_index_container < Foo, boost::multi_index::indexed_by < boost::multi_index::ordered_unique < boost::multi_index::identity < Foo >, LessThanNumeric >, boost::multi_index::ordered_unique < boost::multi_index::identity < Foo >, LessThanText > > > Foo_; where LessThanNumeric (and LessThanText, too) looks like this: struct LessThanNumeric: std::binary_function< Foo, Foo, bool > { bool operator () ( const Foo& x, const Foo& y ) const { return x.NumericKey () < y.NumericKey (); } }; My source is at <http://www.idio.com/misc/mi-test.cpp> Anyone got any tips? Thanks! -- -- Marshall Marshall Clow Idio Software <mailto:marshall@idio.com> It is by caffeine alone I set my mind in motion. It is by the beans of Java that thoughts acquire speed, the hands acquire shaking, the shaking becomes a warning. It is by caffeine alone I set my mind in motion.

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boost::filesystem -- "Aborted"
by matthias 31 Jan '05

31 Jan '05

Hi, I am currently writing a gtkmm component which acts as a file browser, much like a small filemanager which can be embedded in gtkmm applications as a scrolled window. I have just rewritten the component to use the boost::filesystem classes instead of the C functions for interacting with the filesystem. However I am getting a strange error when I start my app: When iterating through a directory I suddenly get the message: Aborted. void FileBrowser::rebuild_file_list() { namespace boostfs = boost::filesystem; boostfs::path cur_path( m_cur_dir ); FileContainer tail; // m_files will first only contain directories, // while tail will contain only files m_files.clear(); try { boostfs::directory_iterator end; for( boostfs::directory_iterator dir( cur_path ); dir != end; ++dir ) { std::cout << (*dir).string() << std::endl; if( boostfs::is_directory( *dir ) ) m_files.push_back( *dir ); else tail.push_back( *dir ); } } catch( std::runtime_error & e ) { std::cerr << e.what() << std::endl; } m_files.sort( SortedByName() ); tail.sort( SortedByName() ); drx::list_concat( m_files, tail ); } OUTPUT: [...] /home/mkay/.acrobat /home/mkay/.synce /home/mkay/.gimp-2.0 /home/mkay/.fonts /home/mkay/.designerrctb2 /home/mkay/.eclipse /home/mkay/.gftp /home/mkay/.ntrc_2 /home/mkay/.DCOPserver_anthrax__0 /home/mkay/.DCOPserver_anthrax_:0 /home/mkay/.kpackage /home/mkay/.fonts.conf /home/mkay/.xscreensaver /home/mkay/xdefaults_old /home/mkay/.reslisarc /home/mkay/.aMule /home/mkay/.gtkrc Aborted At this point the application exits. Any idea what is causing this? Thanks in advance, Matthias

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enabling boost::threads for HP-UX
by Oliver Kowalke 31 Jan '05

31 Jan '05

Hi, I want to use boost on HP-UX together with gcc-3.3.2. As I figured out that thread-support is disabled (BOOST_DISABLE_THREADS is defined in file boost/config/platform/hpux.hpp). Up gcc-3.3 posix-threads are supported on HP-UX-plattform (http://gcc.gnu.org/install/specific.html#hppa*-hp-hpux11) Is it then save to remove #define BOOST_DISABLE_THREADS in boost/config/platform/hpux.hpp? with best regards, Oliver -- "Der Spezialist ist ein Barbar, dessen Unwissenheit nicht allumfassend ist." Master's Voice, S.LEM

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Setting the path to use Boost
by Grek 31 Jan '05

31 Jan '05

Hi fellow Boost users! I am new to the Boost Graph Library (BGL) and I have a query about setting the path to access the library. My platform is Cygwin. I want to use the g++ command and incorporate the BGL in it. How do I go about it? Let's say that I want to use the dijkstra's algorithm. I set the path as follows: boost_1_32_0/libs/graph/example Then I typed the following. g++ -g dijkstra-example.cpp But it displays error messages and I do not know how to proceed. It would be of great help if anyone could tell me how one has to set the path to use the dijkstra's algorithm in a program. Thanks for taking the time to read through this! Cheers Grek --------------------------------- Do you Yahoo!? Yahoo! Search presents - Jib Jab's 'Second Term'

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atlanta statics...
by Jeffrey Holle 31 Jan '05

31 Jan '05

http://houseandhome.msn.com/pickaplace/comparecities.aspx?FromState=WA&From… Hope this link works for you. It takes 5 min. to load a page from website for me. Microsoft's MSN uses windows technology now I guess... The big thing that stands out for me is crime. Seattle is above the national average by about 2x, Atlanta appears to be between 7 and 8 times! I'll have to consider such a move with care....

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Thread stack size
by Thorsten Froehlich 30 Jan '05

30 Jan '05

Hi, Googling I found a thread "Boost.Threads. Anything happening?" (in July 2004) in comp.lang.c++.moderated that suggests there should be a development branch of the thread code that already supports this feature. Unfortunately I cannot find the right branch for it in the boost CVS (using the web CVS viewer). The thread_dev and thread_development branches I found do not appear to be the correct ones as they have not been changed for a very long time and the above mentioned thread suggests it would be a rather recently added feature. While I could add this feature myself for the platforms that I need, I would prefer to avoid duplicating work already done. Could someone point me where to find the branch referred to in the above mentioned comp.lang.c++.moderated thread? Regards, Thorsten Froehlich

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