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[multiindex] hashed index, modify() and traversal
by Francesco Biscani 30 Oct '06

30 Oct '06

Hello, I'm modifying the elements of a multiindex container by accessing them through an hashed index (I suppose that this is faster than accessing them through the other index, which is ordered). I would like to know if I can keep going ++ on the hashed iterator as the elements of the container get changed, without modifying the same elements more than once or reaching the end() prematurely. In other words, does the re-hash change the relative positions of the elements or are they unaltered as the elements are modified? Thanks very much, Francesco

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filesystem::path noobish question
by Nick Dimiduk 30 Oct '06

30 Oct '06

As per the subject line, I have a rather noobish question about using the boost::filesystem tools, specifically the path object. The idea here is that I want to start my program by removing the "tmp" directory in the current process context if it exists to ensure a clean working environment for the remainder of the process. To the code: ... boost::filesystem::path tmp_dir ("tmp", boost::filesystem::native); // get a native handle for "./tmp" boost::filesystem::remove_all (tmp_dir); // clean out this tree in the fs ... This code acts as expected on linux. On windows, it causes a crash. The debugger shows the tmp_dir.m_path._Bx is a bad pointer, indicating to me that the constructor failed somewhere along the way. My questions are these: (1) Is there any error checking I can perform to verify that the path() constructor succeeds, such as a null pointer value or a boolean flag within the data type? (2) Is there something about my code which is linux/POSIX specific? (3) Am I missing something else entirely? I'm using boost 1.33.0 and have a mess of other functioning code which suggests that my configuration/installation is correct on both platforms. Thanks in advance! -Nick Dimiduk

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[graph] incremental_components
by Chris Weed 30 Oct '06

30 Oct '06

Hi, I am trying to use incremental connected components to find the connected components of an image as I randomly add pixels to the image. I calculate the number of components after each pixel is added. This crashes part way through. Any help would be greatly appreciated. Chris #include <boost/graph/graph_utility.hpp> #include <boost/graph/adjacency_list.hpp> #include <boost/pending/disjoint_sets.hpp> #include <boost/graph/incremental_components.hpp> #include <algorithm> #include <numeric> #include <boost/multi_array.hpp> int main() { // Image size size_t width = 100; size_t height = 100; // Create vector of randomized indices std::vector<size_t> indices(width*height,1); indices[0] = 0; std::partial_sum(indices.begin(),indices.end(),indices.begin()); std::random_shuffle(indices.begin(),indices.end()); // Create image which holds which pixels were stored by their linear index boost::multi_array<size_t,2> added_pixels(boost::extents[height][width]); for(size_t i=0;i<height;++i) for(size_t j=0;j<width;++j) added_pixels[i][j] = 0; using namespace boost; typedef adjacency_list<vecS,vecS,undirectedS> Graph; typedef graph_traits<Graph>::vertex_descriptor Vertex; typedef graph_traits<Graph>::vertices_size_type size_type; Graph G(indices.size()); std::vector<size_type> rank(num_vertices(G)); std::vector<Vertex> parent(num_vertices(G)); typedef size_type* Rank; typedef Vertex* Parent; disjoint_sets<Rank,Parent> ds(&rank[0],&parent[0]); initialize_incremental_components(G,ds); incremental_components(G,ds); // Loop over indices and add pixels to image, and edges to graph std::vector<size_t>::iterator b_iter = indices.begin(); for(;b_iter!=indices.end();++b_iter) { size_t r = (*b_iter)/width; size_t c = (*b_iter)%width; size_t j = *b_iter; added_pixels[r][c] = j; if(r>0 && added_pixels[r-1][c]) { add_edge(j,added_pixels[r-1][c],G); ds.union_set(j,added_pixels[r-1][c]); } if(r<(height-1) && added_pixels[r+1][c]) { add_edge(j,added_pixels[r+1][c],G); ds.union_set(j,added_pixels[r+1][c]); } if(c>0 && added_pixels[r][c-1]) { add_edge(j,added_pixels[r][c-1],G); ds.union_set(j,added_pixels[r][c-1]); } if(c<(width-1) && added_pixels[r][c+1]) { add_edge(j,added_pixels[r][c+1],G); ds.union_set(j,added_pixels[r][c+1]); } // After each pixel is added and connected, compute the number of cc's typedef component_index<unsigned int> Components; Components comp(parent.begin(),parent.end()); std::cout << comp.size() << std::endl; } return 0; }

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Re: [Boost-users] [Boost.Parameter] How to Use Named Parameters in a Class Hierarchy?
by Wu Yinghui, Freddie 30 Oct '06

30 Oct '06

> On 10/26/06, *Wu Yinghui, Freddie* <yhwu(a)volumeinteractions.com > <mailto:yhwu@volumeinteractions.com>> wrote: > > > My situation is like this: > > I have a class hierarchy briefly shown as below (assuming virtual member > function template is allowed, just to demonstrate the idea): > ===== CODE ===== <snip> > ===== CODE ===== > > To use the class hierarchy, my program loads the DLL requested by user > using LoadLibrary() (We're using Windows, but it should be similar to > Linux, I suppose), and makes use of the Derived1/Derived2 classes via a > pointer to the Base class. > > Since I have no information about the derived classes when building my > main executable (only Base class is known then), I cannot make direct > use of Derived1/Derived2 types in my main program. -- Yet, I need a way > to provide some arbitrary set of arguments to the derived classes. > > Hope my explanation clears your doubts. Do you have any suggestion or > alternative design in mind? > > > Pass your params packaged in a adobe::dictionary_t (opensource.adobe.com > <http://opensource.adobe.com>) or something like that - not sure what > the boost equivalent is. > > Tony Thanks Tony. Due to our development policy, however, I cannot easily introduce the libraries from Adobe. :( But looking at the reference for adobe::dictionary_t, however, makes me believe that I can replace it with std::map<std::string, boost::any> to certain extent. In any case, I've been trying to build something that use Boost.Parameter naturally (as named parameters to a function). I'll consider if the alternative approach can satisfy all our requirements first. Cheers, Freddie -- Wu Yinghui, Freddie Research & Development Senior Software Engineer Volume Interactions Pte Ltd 1 Kim Seng Promenade, #12-01 Great World City East Tower Singapore 237994 Tel: +65 62226962 (Ext 216) Fax: +65 62226215 Email: yhwu(a)volumeinteractions.com URL: http://www.volumeinteractions.com Important: This message is intended for the recipient(s) addressed above. It contains privileged and confidential information. If you are not the intended recipient, please notify the sender immediately by replying to this message and then delete it from your system. You must not read, copy, use, or disseminate this communication in any form. Thank you.

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Is it a good style about boost::format( format-string ) % arg1 % arg2 % ... % argN
by William Xue 29 Oct '06

29 Oct '06

Hi, First, I am a new user of boost. I wonder of the style of 'boost::format( format-string ) % arg1 % arg2 % ... % argN'. I think it, format(...), as a function, but it seems not function in C or C++ style. % arg1 % ... seems like a group of parameters, if so, why not use '(' and ')' to wrap them? As it works, there must be something I don't know. Please feel free to point out what I am wrong. I'm very glade to know them. Thanks! -- Sincerely yours, William

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Boost.Regex hangs with large pattern
by Dave Druelinger 29 Oct '06

29 Oct '06

I'm using Boost.Regex to match a long, complicated pattern to between 30 and 50 long strings. I loop through and call regex_search until it doesn't find any more matches in the current string and then it moves on to the next string. The problem is that when it has looped through about 40 of the strings, Boost.Regex will hang on the regex_search() function, and it will just sit there processing forever. If I reduce the number of strings I match against there is no problem; 20-30 iterations works like a charm. It also seems to help if I reduce the size of the regex pattern. Frankly I have no clue what could be causing the problem, and any help would be greatly appreciated. Thanks

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Re: [Boost-users] [Boost.Parameter] How to Use Named Parameters in a Class Hierarchy?
by Wu Yinghui, Freddie 27 Oct '06

27 Oct '06

-----BEGIN PGP SIGNED MESSAGE----- Hash: RIPEMD160 > Wu Yinghui, Freddie wrote: > > [snip] > >> >> The situation is like this: In the pseudo-code you provided, DoWork() >> function is declared in the Base class, and is overridden by Derived1 >> and Derived2, with a fixed number of arguments. My problems is that, >> my base class cannot predict the exact number of parameters that a >> derived class may have. (A derived class may have 10 parameters, >> while another may have none.) So it looks a little bit out-of-shape >> in terms of the OO programming style I'm familiar with if I'm going >> to provide overloads of DoWork() for all the possible parameters used >> by all derived classes (not to mention the undesirable dependency >> introduced). > > In order to know which parameters to send through the interface, you'll > have to know the exact subclass? Sorry, that doesn't make sense. > > What's the real problem you are trying to solve - could Boost.Variant + > static_visitor (or some other variant on the Visitor pattern) help? > > / Johan My situation is like this: I have a class hierarchy briefly shown as below (assuming virtual member function template is allowed, just to demonstrate the idea): ===== CODE ===== class Base { //... // This is the function that makes use of Boost.Parameter template <typename ArgumentPack> virtual void Configure(ArgumentPack const &arguments) = 0; }; // This class resides in Derived1.dll class Derived1 : public Base { template <typename ArgumentPack> void Configure(ArgumentPack const &arguments) { //... } }; // This class resides in Derived2.dll class Derived2 : public Base { template <typename ArgumentPack> void Configure(ArgumentPack const &arguments) { //... } }; ===== CODE ===== To use the class hierarchy, my program loads the DLL requested by user using LoadLibrary() (We're using Windows, but it should be similar to Linux, I suppose), and makes use of the Derived1/Derived2 classes via a pointer to the Base class. Since I have no information about the derived classes when building my main executable (only Base class is known then), I cannot make direct use of Derived1/Derived2 types in my main program. -- Yet, I need a way to provide some arbitrary set of arguments to the derived classes. Hope my explanation clears your doubts. Do you have any suggestion or alternative design in mind? Cheers, Freddie - -- Wu Yinghui, Freddie Research & Development Senior Software Engineer Volume Interactions Pte Ltd 1 Kim Seng Promenade, #12-01 Great World City East Tower Singapore 237994 Tel: +65 62226962 (Ext 216) Fax: +65 62226215 Email: yhwu(a)volumeinteractions.com URL: http://www.volumeinteractions.com Important: This message is intended for the recipient(s) addressed above. It contains privileged and confidential information. If you are not the intended recipient, please notify the sender immediately by replying to this message and then delete it from your system. You must not read, copy, use, or disseminate this communication in any form. Thank you. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (MingW32) iD8DBQFFQMFlIgDxhB4QTtMRA5JAAJ0fxjjw9IOlBOr+m2ccXD5d0Sh1EwCeKSJs /NhscTXToOeUpTgwsNBNkr8= =Kb9r -----END PGP SIGNATURE-----

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Re: [Boost-users] Support for VS 2005 C++/CLI
by John Dunn 27 Oct '06

27 Oct '06

Pedro Lamarão said : > > I've suffered much with this in the past. > In my experiente if you try to fool the CLR and actually > compile your DLL withouth /NOENTRY random things may happen > from time to time. I'm not using any DLLs - I'm statically linking to libboost_threads. I'm confident of this since if I define BOOST_THREAD_USE_DLL it will complain about not being able to find the DLL instead of just crashing. Interestingly enough, if I define BOOST_THREAD_USE_DLL it works perfectly fine. So the issue is with linking to the static lib, not the dynamic one. Are you aware of any issues with static libs / initialization and the CLR? That seems to be the case here. John

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Re: [Boost-users] Support for VS 2005 C++/CLI
by John Dunn 27 Oct '06

27 Oct '06

> I'm out of ideas. :-) There isn't anything actively > CLI-hostile in the thread library as far as I know. You could > try stepping into the program with the debugger and see what > causes the error, but if it's the .NET loader not liking it > for some reason, this might not help. You best bet is > probably to report the problem to Microsoft somehow, since it > seems like a legitimate regression. Unfortunately the debugger doesn't help - the error isn't caught by the debugger as far as I can tell. I know I've seen problems with my code when using static objects in non-managed code. I think it might be related to the order in which initialization code is run. Anyone know of a good way to contact MS about compiler issues? I've tried in the past and it's never really been obvious that anyones even read my bug reports. I guess I'll start my posting in the MS newsgroups. Thanks- John

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Regex assign raising exceptions
by Joshua Stewart 27 Oct '06

27 Oct '06

Hi everyone, I am having some issues with the boost::regex assign method. I have been following an example on the boost site for a search and replace. However I seem to be getting an Empty Expression exception when assigning my expression to my boost:regex object. boost::regex exp; const char* expression_string = "([[:space:]](|-)[[:digit:]]+)f;"; exp.assign(expression_string); Any ideas? I have tried a few different syntax option types at the end without success. Thanks Josh Ps. I posted this in comp.lang.c++ before realising that this is probably the better place to ask boost questions :-) This message contains confidential information and is intended only for the individual(s) named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail. Please immediately delete it and all copies of it from your system, destroy any hard copies of it, and notify the sender. E-mail transmission cannot be guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. To the maximum extent permitted by law, Immersive Technologies Pty. Ltd. does not accept liability for any errors or omissions in the contents of this message which arise as a result of e-mail transmission.

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