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undirected graph cycle
by magh＠lehigh.edu 27 Dec '03

27 Dec '03

Is there any easy way to use DFS visitors to return a cycle in an undirected graph? The examples show how to detect if a cycle exists. How do you actually extract it? For my instance, I am dealing with an undirected graph that is a 1-tree, i.e., I know there is exactly one cycle. Thanks, Matt ------------------------------------------------- This mail sent through IMP: http://horde.org/imp/

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date_time: number of days between dates
by Lars Schouw 25 Dec '03

25 Dec '03

I found a solution: long no_days(boost::gregorian::date d1, boost::gregorian::date d2) { using namespace boost::gregorian; using namespace boost::posix_time; date_period dp(d1, d2); return dp.length().days(); } --------------------------------- Do you Yahoo!? Yahoo! Photos - Get your photo on the big screen in Times Square

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date_time converting from date to number of days
by Lars Schouw 24 Dec '03

24 Dec '03

I want to find the number of days in-between two days. What is the easiest way to do this? I am using the date_time lib and want to find the number of days from the time_t started. ptime timet_start(date(1970,1,1)); ptime t(d); time_duration diff = t - timet_start; ptime t123(diff); // timeval tv; //drop off the fractional seconds... // tv.tv_sec = diff.ticks()/time_duration::rep_type::res_adjust(); return 0; // return difference.days; Lars Schouw --------------------------------- Do you Yahoo!? Yahoo! Photos - Get your photo on the big screen in Times Square

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lexical_cast and whitespace, part 2
by Miro Jurisic 18 Dec '03

18 Dec '03

I was trying to do the following: class MyString; std::istream oprator>>(std::istream&, MyString&); std::string s1 = "Hello, World"; MyString s2 = lexical_cast <MyString> (s); It doesn't work. The reason for it failing is: a. the semantics of operator>>(std::istream&, MyString&) are identical to the semantics of operator>>(std::istream&, std::string&) b. the semantics of operator>>(std::istream&, std::string&) are to read the stream up to the first whitespace (as per the stream locale) c. lexical_cast uses (via lexical_stream) operator>>(std::istream&, MyString&) to read the data into MyString The upshot of this is that lexical_cast writes "Hello, World" to the stream (via operator<<(std::ostream&, const std::string&)), reads off "Hello," to MyString (via operator>>(std::istream&, MyString&)), and then throws a bad lexical_cast after noticing there's data left on the stream. The natural question is why it is that this works when converting to a std::string; it seems that it should have the same problem. The answer is that boost::detail::lexical_stream has a lexical_stream::operator>>(std::string&) which ignores whitespace, thus working around the problem if (and only if) the target type of the cast is std::string. Attempting to use lexical_cast with any string type other than std::string fails when the source data contains (non-trailing) whitespace. This is suboptimal. I am going to try a workaround shortly, by partially specializing lexical_stream, but that's just a workaround. I don't see any way to do this without a. breaking the lexical_cast abstraction barrier (as I am about to do) or b. making the semantics of operator>>(istream&, MyString&) differ from those of operator>>(istream&, std::string&) I don't think either of those is the rigt answer. Is there one? Shouldn't there be one? Thanks, meeroh

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Problems with Multi Threaded Version
by Zeros and Ones 18 Dec '03

18 Dec '03

So far I was using the Single Threaded Run Time Library and had no trouble with Boost, however I switched to useing the Run Time Versions just now and found that nothing seemed to work and the error that I get is: "Boost_Regex_vc7_mdid.dll was not found. Re-installing the application may fix this problem" However, the instructions on the website state : "Finally when you use regex++ it is only necessary for you to add the <boost> root directory to your list of include directories for that project. It is not necessary for you to manually add a .lib file to the project; the headers will automatically select the correct .lib file for your build mode and tell the linker to include it. " Im using VC7, and I cant understand why I get this error, do I need to change some setting while linking to the multi threaded versions? For now, I copied the two dll's _boost_regex_vc7_mdid.dll and _boost_regex_vc7_mdi.dll to my working directory and I have a working application, but Im foxed and I would like to know what im doing wrong! Thanks. "Zeros Bits and Bytes"

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BGL and reversing / moving edges
by joshrose 17 Dec '03

17 Dec '03

G'day, I was hoping someone might be able to tell me if they've run into any situations using BGL where they needed to move (or reverse (i.e. flip the source and target)) an edge within a graph implemented as an adjacency_list. I'm working on an implementation of an algorithm for max. weight bipartite matching ("the assignment problem"), and one of the assumptions in the algorithm is that non-matched edges are directed from one subgraph, A, to the other subgraph, B, and matched edges are directed the other way. Over the course of growing the matching, a simple way to add and remove edges from the candidate set is just to reverse the edge, thus the need for some way to reverse the edge within BGL. I don't think I can just remove and then re-add the edge in the other direction, primarily because doing so will (I believe) invalidate any edge_descriptors referring to that edge. In particular, there are property maps keeping track of the weight of edges, the predecessors of certain nodes, etc. that use edge descriptors as keys. I've spent a fair bit of time reading the documentation and looking through the implementation of adjacency_lists (incl. edge_list_impl), and I'm not really sure of a way to either move an edge directly within a graph, or even to create a new edge from another s.t. they have the same edge_descriptor (in general a bad thing, probably). Anyone have any thoughts on this? Thanks, -Josh

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Re: [Boost-users] Newbie question: block read inputs to regex
by annirak＠shaw.ca 17 Dec '03

17 Dec '03

----- Original Message ----- From: John Maddock <john(a)johnmaddock.co.uk> Date: Saturday, December 13, 2003 4:06 am Subject: Re: [Boost-users] Newbie question: block read inputs to regex > > I'm using regex_grep() to search through file contents for > matches. I > want to read the file in blocks to keep memory use down for large > files.What I want to know is whether there is some way of adding > the next block of > memory to the grep where the last one left off. > > > > The best solution I can come up with is using some sort of > double-buffering scheme, but that would take an awful lot of > memory copies > and searching some text multiple times. Both things I would > prefer to > avoid. > > > > What can I do? > > Have you looked at the partial match examples - there is one that > searches a > file in chunks. > > John. Ah, thank you, somehow I had missed that. --Brendan

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Boost Software License: redistribute modified works?
by Steve M. Robbins 16 Dec '03

16 Dec '03

Hi, I've a question for the drafters of the Boost Software License - Version 1.0 - August 17th, 2003. Put yourself in the position of someone who wants to redistribute a modified version of Boost. For example, the linux distributors like Debian. The license begins with the permission grant: Permission is hereby granted, free of charge, to any person or organization obtaining a copy of the software and accompanying documentation covered by this license (the "Software") to use, reproduce, display, distribute, execute, and transmit the Software, and to prepare derivative works of the Software, and to permit third-parties to whom the Software is furnished to do so, all subject to the following: [... a restriction and a disclaimer paragraph ...] As I read this, "the Software" means "the unmodified tar or zip file obtained from boost.org". Is that correct? I'm permitted to "prepare derivative works of the Software", but the license doesn't specify what I may do with my derivative works. Clearly, I may distribute "the Software", but may I distribute the derivative work? Some licenses (e.g. the BSD and the GPL) make it clear that the terms apply to both the software and to derivative works. Shouldn't the boost license do likewise? -Steve

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building boost libraries on Solaris
by K. Herman Chen 16 Dec '03

16 Dec '03

Has anyone built Boost Libraries using Sun/Solaris CC? I first built bjam using gcc on Solaris. But in the next step, 'bjam "-sTOOLS=CC"' (ie Solaris CC), it failed miserably. Since CC is not in the Supported Toolsets, does it mean I cannot build Boost libraries using Sun/Solaris CC? Any pointers would be appreciated. Thanks. herman

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msvc-stlport creates name mangled functions with std:: not _STL::
by John Bustard 16 Dec '03

16 Dec '03

I can't seem to link with the filesystem lib when built with the following options: rem Get environment right for compiler -- comment out after first run rem "C:\Program Files\Microsoft Visual Studio\VC98\Bin\VCVARS32.BAT" rem Setup for Boost.Python rem Setup for Boost 'toolset' set STLPORT_PATH=C:\ set STLPORT_4.6_PATH=C:\STLport-4.6 set STLPORT_VERSION=4.6 bin.ntx86\bjam "-sTOOLS=msvc-stlport" "-sBUILD=<stlport-iostream>on" the name mangled function that is exported is ?leaf@path@filesystem@boost@@QBE?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@XZ but the function that msvc tries to link with is: ?leaf@path@filesystem@boost@@QBE?AV?$basic_string@DV?$char_traits@D@_STL@@V? $allocator@D@2@@_STL@@XZ Two things I've noticed that are a bit wierd are that the boost libs are put in stlport-4.5.3 directory even when built with the options directing it to 4.6. Also stlport has an option to put itself in the std namespace but merely #defines std as _STL so I would have expected the exported function from the boost library to be _STL not std. Any ideas, thanks John

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