- Boost-users - lists.boost.org

RE: [Boost-Users] shared_ptr in Borland C++ Builder
by scleary＠jerviswebb.com 12 Jun '02

12 Jun '02

> From: Craigus [mailto:yg-boost-users@m.gmane.org] > > Hi > > I'm new to using the Boost library. Welcome! :) > I have Codeguard turned on (detects memory leaks, accessing freed memory, > overwriting memory illegally and the like). When the shared_ptr object > count goes to zero operator() in checked_deleter eventually gets called. > Codeguard is reporting (in poor English): > > Method called on illegally casted object If you want to fix the problem: uncheck Project Options -> C++ -> Zero length empty class members. Then rebuild (not remake). The rest of this e-mail is just explaining what the error is and why this fixes it. Here's the problem: CodeGuard is complaining that the 'this' pointer for the checked_deleter object is invalid when its operator() is called. (The error is not reported if you uncheck the "Validate the 'this' pointer on member function entry" and rebuild). Many function objects contain no data or base classes, but operator() cannot be static, so for these function objects (including checked_deleter), a sort of unspoken convention has arisen: never use the 'this' pointer. But CodeGuard validates the 'this' pointer anyway... In common implementations of Standard C++, CG's validation would work: in the case where a function object is used as a most-derived class, it has non-zero size (according to the Standard), so 'this' would reference a "placeholder" memory location for that object. in the case where a function object is used as a base class, then the most-derived class has non-zero size, and 'this' would reference a member in some derived class. C++ Builder, however, has a non-Standard-conforming option that is on by default: Project Options -> C++ -> Zero length empty class members. This creates a "loophole" in the first case described above: in the case where a function object is used as a most-derived class *as a member of another class*, it has zero-size(!) -- and therefore if it is the last member of that class, 'this' would reference memory *after* the most-derived class. Unchecking this option allows CG's validations to work in the way described above, closing the "loophole". Happy coding! :) -Steve

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bit_iterator
by Jan Langer 12 Jun '02

12 Jun '02

hello, i do use iterator adaptor to build a bit_iterator, which return single bits of the elements of an underlying iterator. the base_type of my iterator_adaptor is std::pair <BaseIterator, unsigned int> representing the iterator and the bit position. now my iterator does not work if i adapt istreambuf_iterator because self operator++(int) { self tmp(*this); ++*this; return tmp; } of iterator_adaptor is not able to use the proxy returned by the postfix increment of the input iterator. now i searched the archive and found in: Subject: Re: [boost] (infinite) sequences using recurrence relations From: Corwin Joy < cjoy@xxxx > Date: Fri, 10 Aug 2001 01:21:28 -0500 the following sentence: >In table 72, p. 511 of the standard you will notice something weird about >the postfix increment operator: >Namely, it is specified as (void)r++. >In other words, unlike all other standard iterator types, an input iterator >is not required to return a copy of its old value! but this would mean that the expression *i++ is wrong in most cases. is there a trick to make iterator_adaptor also handle this case or shall i hope that nobody types *i++ with my bit_iterator based on such an input iterator, or did i understand something incorrectly? regards -- jan langer ... jan(a)langernetz.de "pi ist genau drei"

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shared_ptr in Borland C++ Builder
by Craigus 12 Jun '02

12 Jun '02

Hi I'm new to using the Boost library. I'm using the shared_ptr because I can't do what I want to do with the std::auto_ptr (which is to have them stored in other STL containers). I ran into the following problem in C++ Builder 5, patch 1- I have Codeguard turned on (detects memory leaks, accessing freed memory, overwriting memory illegally and the like). When the shared_ptr object count goes to zero operator() in checked_deleter eventually gets called. Codeguard is reporting (in poor English): Method called on illegally casted object It doesn't matter what type the shared_ptr holds. I even tried a console program that contains only the following line (apart from return 0; of course :-): boost::shared_ptr< int > tmp( new int ); As soon as that object goes out of scope it is destroyed and operator() is called as I indicated above and Codeguard reports the error. Has anyone else seen this behaviour ? I was originally using Boost 1.27, which gave me the same error when I used the reset method. I downloaded 1.28 and that went away so that now it's only happening when the actual shared_ptr object is destroyed. I don't have much idea of what's going on inside the shared_ptr, so I don't even know where to start looking. Any help will be much appreciated. Thanks Craigus

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Re: Re: How to use Iterator Adaptors?
by David Abrahams 12 Jun '02

12 Jun '02

"Duane Murphy" <duanemurphy(a)mac.com> wrote in message news:20020610181043.12388@mail.murphyslogic.com... > --- At Tue, 4 Jun 2002 13:02:08 +0100, Keith MacDonald wrote: > > >> So, what is the "normal" way of creating an iterator out of thin air as > >> it were? > > > >That was the question in my mind, which the first sentence of the Iterator > >Adaptors documentation led me to hope it would answer: "The Iterator Adaptor > >library allows you transform an arbitrary ``base'' type into a > >standard-conforming iterator". If the base type is a container, how do you > >do it? > > Keith, > Your email was delayed in my queue for some reason. Were you able to > figure out how to do an iterator from a container from the discussion > between Dave Abrahms and myself? Well, of course you have to think about what data the iterator will need in order to do the iteration. The Base type can't be just a container if you want the iterator to traverse the container's elements -- you need to store some indication of the position within the container -- e.g. a node pointer, and index, or an interator -- as (part of) the Base type. -Dave

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[BGL]
by Angelique Michaut 12 Jun '02

12 Jun '02

Hello, I use the BGL to read a graphviz file and I do a depth_first_search on the graph. I would like to determine the fontname (times-roman for example) the fontcolor (black for example) and the position of each node when the depth_first_search is done. Could you help me? Thinks

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How to use Iterator Adaptors?
by keithmac66 11 Jun '02

11 Jun '02

Hi, I'm struggling to understand how to use Iterator Adaptors, due to a lack of simple examples. This is disappointing, given that supposedly "Using iterator_adaptor, you can easily implement an iterator class" (www.boost.org/libs/utility/iterator_adaptors.htm) Can anyone help, by explaining how to implement a random access iterator for a custom collection class? e.g.: template <class T> class DumbCollection { public: DumbCollection(T data[10]) { for (int i = 0; i < 10; i++) m_data[i] = data[i]; } iterator begin(); iterator end(); private: T m_data[10]; }; Thanks, Keith

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how to compile the boost/regex without comand line
by Aza Lsaja 11 Jun '02

11 Jun '02

Hi, I'm new on this list as well as on C++ world. I try to install boost library but failed. This is what I did: [Win98, MSVC 6.0 without service pack] 1. Download and extract the zip file to root directory. I have C:\boost_1_27_0 now. (success) 2. Download Boost.Build for windows from sourceforge, unpack and installing, reboot (success) 3. go to c:\boost_1_27_0 directory, then execute this in command prompt: jam -sBOOST_ROOT=. -sTOOLS="msvc" (fail) the dos prompt yield many lines but I cant read it. It's too fast. I think it's error messages. Or maybe I missing some procedure? please let me know. I guess my compiler is broken and I need MSVC service pack. But, I can't download it at this time. Acctually, I just want to use the boost's regex library. Can I compile the regex manually (by the IDE) so I can use it with include ( #include <boost/regex.hpp> ) in my codes? If yes, how? Sorry for my english, I hope you understand me. Thanks. Aza ------------------- Kemudahan Hosting PlasaCom ---------------------------------- Hosting menjadi lebih mudah dan murah dengan keringanan 50% biaya registrasi mail hosting dan webhosting selama bulan Juni 2002. Klik http://idc.plasa.com untuk pendaftaran ---------------------------------------------------------------------------------

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[BGL] How can my visitors visit?
by �ڱ�� 11 Jun '02

11 Jun '02

Compiling below, It's OK. but executing, visitors do nothing. What's the problem? Is this slicing problem? why? thank you in advance. ---------------------- below ------------------------ // bfs visitor 1. just printing every vertex in breath first order. struct graph_printer1 : public default_bfs_visitor { template<typename Vertex, typename Graph> void discover_vertex(Vertex u, Graph& g) { cout << " graph printer 1" << u <<"\n"; } }; // bfs visitor 2. same as visitor 1 except message. struct graph_printer2 : public default_bfs_visitor { template<typename Vertex, typename Graph> void discover_vertex(Vertex u, Graph& g) { cout << " graph printer 2" << u <<"\n"; } }; // graph wrapper class graph_wrapper { protected: adjacency_list<vecS, vecS, bidirectionalS, VertexProperty, EdgeProperty> m_graph; public: // HERE. this Visit function does nothing.!! void Visit(default_bfs_visitor* vis, int vertexID ) { breadth_first_search(m_graph, vertex(vertexID, m_graph), visitor(*vis)); } }; int main() { graph_wrapper holder; graph_printer1 vis1; graph_printer2 vis2; holder.Visit(&vis1); holder.Visit(&vis2); return 0; } ---------------------------------------- Ki-Soo, Park e-mail: park(a)erhouse.co.kr wfms123(a)hotmail.com

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Hi!
by rajanik3 11 Jun '02

11 Jun '02

Hi! Could some body tell me how to use boost libraries in Unix. I am using tcsh shell. After downloading, what should I change in order for the compiler to locate the boost library headers. Thanks, Raj.

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thread::join() usage
by rgalek2002 10 Jun '02

10 Jun '02

Hi, I have an application which starts a number of threads, and I want the application to wait for the threads to finish before exiting. Standard stuff, I know, but never having used threads before I am wondering what the stadard way is to accomplish this. I have (psuedo code) for (each record in database) { thread thrd(func(), data); } I could imagine storing all my thread objects in a list, and then calling join() on each one. For example something like list <thread> threads; for (each rec in db) { thread thrd(func(), data); threads.insert(threads.begin(),thrd); } list<thread>::iterator i; for (i=threads.begin(); i!=threads.end(); i++) { thread t = *i; t.join(); } Does this seem reasonable? Is there a better/standard way? One thing I don't like here is that each join will block, when what I would like to do is something more like join_all(); Thanks, Rich

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