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RE: [Boost-Users] [BGL] Best way to abort an algorithm from withi n a visitor?
by Jim.Hyslop 18 Sep '02

18 Sep '02

Steve M. Robbins [mailto:steven.robbins@videotron.ca] wrote: > I use that technique to abort the Dijkstra shortest path > search when I find my > goal node. It works fine, as far as I can tell, but I'd be > interested to > learn if there is a better way. It seems anti-idiomatic to me. Exceptions are intended to signify exceptional circumstances that you would not normally expect to encounter (at least according to one school of thought). An exception tells me "Oops, something went wrong here" not "we succeeded, here's the answer". Many of the exceptions I catch are called "oops": try { /* ... */ } catch (std::exception &oops) { /* ... */ } One possible snag might be if your code interacts with someone else's code, which will catch the exception and not pass it on to you. In the context we're talking about, though, I don't see that as a significant problem. An exception is certainly an easy way to abort the search, and since I don't have an alternative to offer, I'll shut up now ;=) -- Jim

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Levenshtein Distance algorithm
by Philippe Lalande 18 Sep '02

18 Sep '02

Hi, I was wondering if anyone could tell me if Boost contains a function that could perform a 'Levenshtein distance' calculation on a sequence. The Levenshtein distance is a measure of the similarity between two strings calculated as the number of deletions, insertions, or substitutions required to transforms the source string to the target string. IMO, it is an interesting algorithm that could apply to any kind of sequence. I'd be happy to discuss interface and implementation on the dev list if such algorithm does not exist yet. Thank you Philippe

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RE: [Boost-Users] Re: Newbie needs help w/VC6 & filesystem (take 2)
by Jim.Hyslop 18 Sep '02

18 Sep '02

John B. Williston [mailto:yg-boost-users@gmane.org] wrote: > On Tue, 17 Sep 2002 12:40:53 -0400, Douglas Gregor <gregod(a)cs.rpi.edu> > wrote: > > >Could you copy 'n' paste some of the link errors you are > getting? It seems > >like you did the right thing (at least, I don't know of a > better way), but > >perhaps knowing what symbols are being redefined would help > isolate the > >problem. > > I sure can. The following is the compile output: > > --------------------Configuration: TestFs - Win32 > Debug-------------------- > Compiling... > Main.cpp > Linking... > LINK : warning LNK4075: ignoring /INCREMENTAL due to /FORCE > specification > msvcprtd.lib(MSVCP60D.dll) : warning LNK4006: "public: __thiscall > [...] already > defined in Main.obj; second definition ignored I've typically found these errors when you have mixed the run-time library usage, or MFC usage. One part of your project wants to link in the C run-time library as a DLL, but another part of your project wants to link it in as a static library. Make sure that all the projects, including the ones that build any libraries you're linking with, use the same "Use runtime library" option (Project | Settings, "C/C++" tab, "Code Generation" category), and also that all projects use the same "Microsoft Foundation Class" option (on the General tab). -- Jim

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checked_delete with pointer template parameter
by Craig Henderson 18 Sep '02

18 Sep '02

I need to free memory from a container with elements of pointers, where the container value_type is a pointer type. I cannot use the checked_delete template as it is, as the template parameter is defined without the '*' pointer. For example, the following fails (obviously): typedef std::vector<char *> X; X x; ... std::for_each(x.begin(), x.end(), boost::checked_delete<X::value_type>); I'm using VC7, so have no partial specialization available, so using the type traits library remove_pointer<> does not work: typedef boost::remove_pointer<typename X::value_type>::type type; std::for_each(x.begin(), x.end(), boost::checked_delete<type>); My existing solution uses a unary functor, as below, but this met with critism on the Boost Developers' list. What would be the 'boost' solution to this problem? template<typename T> class free_heap_ptr : public std::unary_function<T, void> { public: free_heap_ptr() { } ~free_heap_ptr() { } void operator() (T p) { delete p; } }; ... std::for_each(changes_.begin(), changes_.end(), free_heap_ptr<typename change_list::value_type>()); TIA -- Craig

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Is there a Type2Type in boost ?
by Baptiste Lepilleur 17 Sep '02

17 Sep '02

Hi everyone, I've looked around and failed to find the Type2Type template, detailed by Andrei Alexandrescu in a CUJ article (http://cuj.com/experts/1810/alexandr.htm?topic=experts) in boost. While the implementation is trivial: template<typename Type> struct Type2Type { typedef Type original_type; }; I'd rather have it in a well known library. Has it been replaced by something else ? Baptiste.

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Newbie needs help with VC6 & filesystem library
by John B. Williston 17 Sep '02

17 Sep '02

Greetings, Though I'm an "old hand" at C++, I'm a complete newbie when it comes to Boost. The piece that really caught my eye, in light of my current project, is the directory iterator. To date, however, I haven't had any success getting it to compile and function under Win32 with MSVC6, so I thought I would post here. I first have a couple of general questions about using Boost, and then one specific question about the problems with my project at hand. (1) Is there a "right" way to include Boost stuff with VC6? Adding the Boost base directory to my list of include directories seems to work for the official stuff, but it clearly doesn't work for the filesystem stuff because Directory.h is not in the base\boost directory. I can put it there myself, of course, but I'm wondering if there is some intended way to use the beta libraries before they become a part of the whole. (2) Is there a "right" way to link Boost stuff with VC6? The filesystem stuff, like the regex stuff and some other pieces, requires actual compilation and cannot simply be included as header files. I have already built all the official libraries using the bjam utility, but I cannot help noticing they're each stored in hideously long paths beneath the boost base directory. Is there a "right" directory under the Boost hierarchy into which the resulting libs should be copied for ease of inclusion in VC6? Or should I copy them into my project directories as needed? Or should I simply come up with my own system? To get to the more specific question, let me explain how I've addressed (1) and (2) for the time being. Regarding (1), I've copied Directory.h and Boost.h into the base\boost directory so that they may be included without changing the existing source code. That was simple enough. Regarding (2), I've decided to add Directory.cpp to my project and compile it as a module, rather than try to get the linking to work externally. Having said that, consider the following code: #include <windows.h> #include "boost/directory.h" int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) { using namespace boost::filesystem; std::string strFilename; for (dir_it it("./"); it != dir_it(); ++it) if (!get<is_hidden>(it)) strFilename = *it; return 0; } This is an extremely minimal test case of integrating the filesystem stuff into a Win32 application. When compiling the application, I get the following lengthy and inscrutable (to me, at least) error message: WinMain.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: __thiscall boost::filesystem::get<struct boost::filesystem::is_hidden>::get<struct boost::filesystem::is_hidden>(class boost::filesystem::dir_it const &)" (__imp_ ??0?$get@Uis_hidden@filesystem@boost@@@filesystem@boost@@QAE@ABVdir_it@12@@Z) The error message seems to suggest that the filesystem stuff isn't available in my project. I find that confusing because the Directory.cpp module compiles without any errors, and I am thus inclined to think that, in fact, all of the filesystem stuff is in my project. Thus, I must also ask the third question: (3) Can anyone explain to me what I might be doing wrong and, more importantly, how I might correct it? Thanks much to all the Boost authors for an interesting set of tools. And thanks in advance to any who respond for all the help with my specific issue. John

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Newbie needs help w/VC6 & filesystem (take 2)
by John B. Williston 17 Sep '02

17 Sep '02

Greetings, I'm sorry for my earlier post. I didn't realize that the dir_it beta stuff was not what was being referred to as the "filesystem". I now know better, and I'm trying to make the filesystem stuff work instead. Unfortunately, I'm having no better luck. Consider the following code: #include "boost/filesystem/operations.hpp" // includes boost/filesystem/path.hpp #include "boost/filesystem/fstream.hpp" // ditto #include <iostream> // for cout int main(int iArgc, char** pArgv) { namespace fs = boost::filesystem; int iNumNodes = 0; fs::directory_iterator end_itr; // default construction yields past-the-end for (fs::directory_iterator itr("debug"); itr != end_itr; ++itr) { if (fs::is_directory(*itr)) std::cout << (*itr).file_path() << " (dir)" << std::endl; else std::cout << (*itr).file_path() << std::endl; iNumNodes++; } std::cout << iNumNodes << " total." << std::endl; return 0; } That's a relatively brain-dead use, I should think, to enumerate the contents of the debug folder to the console. Unfortunately, when I try compiling this, the linker complains horribly about all kinds of symbols already being defined in the filesystem object modules. To ditch the linker errors, I've temporarily used the /force switch, but that's hardly illuminating. First, can anyone tell me how to avoid getting a plethora of multiply-defined symbol errors? Or is /force my only real option? Second, if I use the /force switch, I get all kinds of unhandled exception errors when the directory iterator is constructing. Changing the string I pass to it at construction just changes which exception it emits. With the code above as written, the culprit is: template<typename Y> void reset(Y * p) // Y must be complete { BOOST_ASSERT(p == 0 || p != px); // catch self-reset errors this_type(p).swap(*this); } That's lines 181-185 of boost/shared_ptr.hpp, and I haven't a clue why it's freaking out. Tracing through all the code shows that the exception is occurring AFTER the swap seems to succeed. I'm stumped as to what the problem might be. But I sure would appreciate any advice y'all can offer. So far I have to say that I'm impressed with the Boost library features, but it seems a cast-iron bitch to make it actually compile and link in any real-world programs. John

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Advantage to STLport w VC7?
by dick.bridges＠tais.com 17 Sep '02

17 Sep '02

I'm preparing an upgrade from VC6 SP5 to VC7. I'm told the VC7 STL was improved but specifics are hard to come by. Can anyone tell me if there's still an advantage, <emphasis> with respect to the Boost libraries</emphasis>, to using STLport with VC7? TIA for any suggestions.

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regex 1.28.0 build (question - and problem report)
by acarsac 17 Sep '02

17 Sep '02

Hi, 2 things while upgrading from 1.25 to 1.28 : -I was trying to build the regex library (1.28.0) with msvc-stlport configuration. vc6.bat set STLPORT_PATH="c:\Mes Documents\STLport-4.5.3" nmake -fvc6-stlport.mak will fail. i had to erase some lines in vc6-stlport.mak because i guess it does not support space in path. i do the install by hand too. unless that, it work fine for me. -I was just wondering why the boost build system (jam) makes the regex library if i need to rebuild them with nmake whereas i specify the good target os for both ? Alex.

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question about edge_property_type
by wei guo 16 Sep '02

16 Sep '02

Hi, group: I have a problem of using edge_property_type. in the example file: undirected.cpp, I added several lines like: template < typename DirectedGraph > void directed_graph_demo() { const int V = 2; DirectedGraph digraph(V); typename graph_traits < DirectedGraph >::vertex_descriptor u, v; typedef typename DirectedGraph::edge_property_type Weight; typename property_map < DirectedGraph, edge_weight_t >::type weight = get(edge_weight, digraph); typename graph_traits < DirectedGraph >::edge_descriptor e1, e2; bool found; ......... Weight w1 = get(weight, e1); // <<----------- added line Weight w2 = get(weight, e2); // put( weight, e1, w1*w2/(w1+w2) ); // <<----------- added line std::cout << "weight[(u,v)] = " << get(weight, e1) << std::endl; std::cout << "weight[(v,u)] = " << get(weight, e2) << std::endl; } I got following compiling errors with KAI compiler: "undirected.cpp", line 83: error: no operator "*" matches these operands operand types are: Weight * Weight put( weight, e1, w1*w2/(w1+w2) ); ^ detected during instantiation of "void directed_graph_demo<DirectedGraph>() [with DirectedGraph=DirectedGraph]" "undirected.cpp", line 83: error: no operator "+" matches these operands operand types are: Weight + Weight put( weight, e1, w1*w2/(w1+w2) ); ^ detected during instantiation of "void directed_graph_demo<DirectedGraph>() [with DirectedGraph=DirectedGraph]" 2 errors detected in the compilation of "undirected.cpp". however, if I change the put statement in the example code to be: put( weight, e1, get(weight, e1)*get(weight, e2)/(get(weight, e1)+get(weight, e2)) ); it compiled successfully. So, what do I missing here, and what is the return type of get(weight, e2) ? and how it connected with DirectedGraph::edge_property_type ? thanks in advance! weiqing --------------------------------- Do you Yahoo!? Yahoo! News - Today's headlines [Non-text portions of this message have been removed]

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