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Don't seed() mersenne_twister RNG with 0
by Benoît SIBAUD 23 Jul '04

23 Jul '04

Hi, a seed(0) with a mersenne_twister (like mt11213b or mt19937) aborts on some assertion (tested on boost 1.31). boost/random/linear_congruential.hpp:61: boost::random::linear_congruential<IntType, a, c, m, val>::linear_congruential(IntType) [with IntType = uint32_t, IntType a = 69069, IntType c = 0, IntType m = 0, IntType val = 0]: Assertion `c || x0' failed. mersenne_twister::seed(x) calls linear_congruential<uint32_t, 69069, 0, 0, /* unknown */ 0>(x), which asserts(0 || x). So x must be non-zero. I didn't see it in the doc, but I think it would be a good thing to have it written down, or to have mersenne_twister::seed() modified to avoid the assertion. Regards, -- Benoît Sibaud

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filesystem and existing files
by Russell Hind 23 Jul '04

23 Jul '04

With filesystem, you can do filesystem::path P(....); filesystem::ofstream S; if (!filesystem::exists(P)) { S.open(P); } But isn't there a race condition here which could lead to a file created by another process being wiped out, or added to? Is there a way to get ofstream::open to fail if the file already exists? It succeeds on VC7.1 but in some situations I don't want it to succeed. Cheers Russell

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Looking for some help with boost::thread::sleep()
by Kutch, Patrick G 23 Jul '04

23 Jul '04

I am used to putting in quick sleep() statements in my worker threads, usually a sleep(0) just to give up a timeslice, or maybe a sleep(1). Of course boost::thread::sleep takes an xtime object not a milliseconds value, so I wrote a small routine to simulate the sleep() statement using boost::thread::sleep: void inline UtilitySleep(long milliSeconds) { const int NANOSECONDS_PER_MILLISECOND = 1000000; if (0 == milliSeconds) { boost::thread::yield(); // just do a yield return; } boost::xtime time; int sec = 0; // if larger than 1 sec, do some voodoo for the boost::xtime struct if (milliSeconds >= 1000) { // convert ms > 1000 into secs + remaining ms int secs = milliSeconds /1000; milliSeconds = milliSeconds - secs*1000; sec += secs; } milliSeconds*=NANOSECONDS_PER_MILLISECOND; // normal boost time sleep stuff // get current time boost::xtime_get(&time,boost::TIME_UTC); // add # of desired secs and ms time.nsec+=milliSeconds; time.sec+= sec; // sleep until that time boost::thread::sleep(time); } It seems to always work fine unde Windows, however occasionally under Linux it appears that if I use a small value, such as sleep(2) that sometimes it takes longer to setup the values and call boost::thread:sleep() and I end up passing an xtime value that has already passed, basically blocking the thread forever. Anybody have any advice for me? Thanx! - Patrick

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Peculiar uBLAS compile error...
by Nicholas Andrews 23 Jul '04

23 Jul '04

Hi, I have the following c++ function: void multi_state_kf::correction(const vector<double>& obs, const matrix<double>& dev) { compute_gain(dev); vector<double> temp = (m*obs-newX*m); x=newX+prod(temp,K); matrix<double> T=identity_matrix<double>(3,3)-K*m; matrix<double> temp2=prod(T,newP); matrix<double> temp3=prod(K,dev); P=prod(temp2,trans(T))+prod(temp3,trans(K)); } The syntax is completely hacked together as this is my first attempt at using boost's uBLAS, but it got rid of most of my errors except this one: \boost\numeric\ublas\functional.hpp(190): error C2440: '=' : cannot convert from 'const boost::numeric::ublas::matrix_binary_scalar2<E1,E2,F>::value_type' to 'double' (...) The odd (for me) part is that even when I remove all boost function calls from the function the compile error still shows up and it points me to a line in the functional.hpp file. So 1. Does anyone know what could be causing this compile error? 2. What's a better way of writing this function? Thanks in advance, Nick

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test failure rate and usage
by JHAYNBERG＠cooperneff.com 22 Jul '04

22 Jul '04

I wanted to use the Boost smart_ptr classes on Solaris 8/Workshop 7 and RedHat E3/gcc 3.23. So, I downloaded the boost src (and jam and boost.build) and built the entire package. After seeing many test failures, I discovered on the regression test page that no compiler achieves 100% pass rate and some are about 30%. I have 2 questions. One, in general, how does one know when it is "safe" to use a boost library on a particular platform? For example, if a platform's failure rate is 15%, should boost be used? And, two, with just the boost source (without building any libraries), I was able to use the boost::shared_ptr in my Solaris application by merely including the right header. Apparently, I don't need to build boost to use shared_ptr which leads me to ask, in general, how do one know when a library is needed (or not needed)? Shouldn't the fact that boost is mainly templates mean there should be little or no implementation (i.e. code that needs to be compiled into a library)? For example, many template libraries are provided as header-only solutions. Thanks! Jay Haynberg Software Engineer This message and any attachments (the "message") is intended solely for the addressees and is confidential. If you receive this message in error, please delete it and immediately notify the sender. Any use not in accord with its purpose, any dissemination or disclosure, either whole or partial, is prohibited except formal approval. The internet can not guarantee the integrity of this message. BNP PARIBAS (and its subsidiaries) shall (will) not therefore be liable for the message if modified. --------------------------------------------- Ce message et toutes les pieces jointes (ci-apres le "message") sont etablis a l'intention exclusive de ses destinataires et sont confidentiels. Si vous recevez ce message par erreur, merci de le detruire et d'en avertir immediatement l'expediteur. Toute utilisation de ce message non conforme a sa destination, toute diffusion ou toute publication, totale ou partielle, est interdite, sauf autorisation expresse. L'internet ne permettant pas d'assurer l'integrite de ce message, BNP PARIBAS (et ses filiales) decline(nt) toute responsabilite au titre de ce message, dans l'hypothese ou il aurait ete modifie.

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Please help me understand boost:lambda
by TP Diffenbach 21 Jul '04

21 Jul '04

I'm having some difficulties figuring out how to use boost::bind and boost::lambda Here's what I've trying to do: use transform to transform the values in one container to another, looking up the new value as a function of the old. What I'm trying to do is conceptually simple: call std::transform with a predicate that takes the original value, does a std::find_if on that value in another "container" using a bound std::greater< int > predicate, converts the returned iterator to an integral distance, and inserts that integral distance in the container that is the destination of the transform. Doing this using a hand-coded functor is easy enough, but I'm not able to figure out how to do it using boost::lambda. If I understand lambda, this should make each element of c equal to four times the corresponding element of o, and indeed this compiles as works as expected. std::transform( o.begin(), o.end(), std::back_inserter( c ), _1 = _1 * 4 ) ; This bit of code will look up a value, the index of the first element in partition with a value greater than v (or 3 if v is greater than all values in partition: int partition[] = { 10, 20, 30 } ; offset = std::find_if( partition, partition + 3, boost::bind( std::greater< int >(), _1, v ) ) - partition ; This code wraps the lookup and the subtraction that turns the returned pointer into an offset: template< template< typename > class Pred, typename It, typename T > int find_region_offset( It b, It e, T val ) { return std::find_if( b, e, std::bind2nd( Pred< T >(), val ) ) - b ; } and this code uses the wrapper, along with the transform: std::transform( o.begin(), o.end(), std::back_inserter( c ), boost::bind( find_region_offset< std::greater, int*, int>, partition, partition + 3, _1 ) ) ; So far, so good. What I don't know how to do is to dispense with the wrapper. As close as I can come is to use this class: struct identityPred { int operator()( int i ) { return i ; } } ; to do this: std::transform( o.begin(), o.end(), std::back_inserter( c ), boost::bind( std::less< int* >(), // to subtract the returned pointer from partition boost::bind( std::find_if< int*, identityPred >, partition, partition + 3, identityPred() ), partition) ) ; This compiles, but I don't want identityPred, I want boost::bind( std::greater< int >(), _1, _1X ) where _1 is the value in the partition array and _1X is the value read from container o. Ideally I'd like to do this using boost::lambda, which I think would look something like: std::transform( o.begin(), o.end(), std::back_inserter( c ), _1 = find_if(partition, partition + 3, _1 > var( _1 )) - partition ) ; where the first and last "_1"s are transform's (containers o and c's) values, and middle one is partition's values. Again, what I'm trying to do is conceptually simple: call transform with a predicate that takes the original value, does a find_if on that value in another "container" using a bound std::greater< int > predicate, converts the returned iterator to an integral distance, and inserts that integral distance in the container that is the destination of the transform. So if someone could point out to me what I'm doing wrong, or point me to more examples of using boost::lambda than are contained in the boost::lambda documentation, or could just tell me that what I'm trying to do isn't possible (and why it's not possible) I'd very much appreciate it. Thanks. PS And a technical trouble: if I include both boost::bind and boost::lambda, and I am using namespace boost::lambda to save qualifying each _1, I get a type redefinition for _1, with one definition in boost::bind, when using gcc under cygwin: b.cpp:49: error: use of `_1' is ambiguous /usr/local/include/boost/lambda/core.hpp:74: error: first declared as `const boost::lambda::placeholder1_type&boost::lambda::<unnamed>::_1' here /usr/local/include/boost/bind/placeholders.hpp:55: error: also declared as ` boost::arg<1> <unnamed>::_1' here b.cpp:57: error: use of `_1' is ambiguous /usr/local/include/boost/lambda/core.hpp:74: error: first declared as `const boost::lambda::placeholder1_type&boost::lambda::<unnamed>::_1' here /usr/local/include/boost/bind/placeholders.hpp:55: error: also declared as ` boost::arg<1> <unnamed>::_1' here Should this be happening?

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date-time
by Jonathan Oulds 21 Jul '04

21 Jul '04

Could anyone explain to me why there is not a default constructor for boost::gregorian::date_time and boost::posix_time::ptime. I implemented a simple constructor where both classes are created as 'not_a_date_time'. The only problem I have had is compiling my code on other peoples machines that do not have my modification to the date_time library. jonathan

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RE: [Boost-users] database lib
by Ajit Jadhav 21 Jul '04

21 Jul '04

Regarding DTL, see http://lists.boost.org/MailArchives/boost/msg13153.php. Not sure where it stands now. > -----Original Message----- > From: boost-users-bounces(a)lists.boost.org > [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Chris > Sent: Wednesday, July 21, 2004 11:13 AM > To: boost-users(a)lists.boost.org > Subject: [Boost-users] database lib > > > Hi all, > > I am wondering if there are any plans to include a database > library, for example for ODBC in the boost library. > > Please bear in mind that I am new to the boost libraries and > find them really cool. > > But like the socket library I found it because of an old > post, so that is why I am asking about the database library. > > Also I found this library really interesting and am using it > in a couple of small spike solutions: > http://dtemplatelib.sourceforge.net/index.htm > (Any comments > on the library are welcome) > > Thanks, > Chris > > > > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/bo> ost-users >

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Testing boost installation
by Tom Puverle 21 Jul '04

21 Jul '04

In our environment it is a requirement that all libraries that are about to be deployed are tested. I would like to know if there is a way in which I can run the regression tests against the installed version of the boost headers and libraries, so that I can check they have been built and installed correctly. Thanks. _________________________________________________________________ Want to block unwanted pop-ups? Download the free MSN Toolbar now! http://toolbar.msn.co.uk/

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boost equivalent to sgi hash_map?
by Stephen torri 21 Jul '04

21 Jul '04

Is there a boost equivalent to SGI hash_map? I am looking for a data structure that taking the key finds the data in one step O(1). Stephen

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FW: boost::filesystem on WIN32: Problem passing pointer of native to path
by Christian Hoffmann 21 Jul '04

21 Jul '04

Hello... We have problems here passing the boost::filesystem::native function as a checker on WIN32 platform, eg. like this ... boost::filesystem::path path ("d:\hello\hello", boost::filesystem::native); ... When we take the address of the function "boost::filesystem::native(...)" in dll A and the pass it to boost filesystem dll, the various comparisons with "native" inside path_posix_windows.cpp:m_path_append ( const std::string & src, name_check checker ) fail, and and the code throws an invalid name exception. (e.g. line 242: if ( (checker == no_check || checker == native) && src.size() >= 2 ) fails as checker != native) The microsoft compiler takes the address into an internal function table, instead of the adress of the "real" boost::filesystem::native () function, so the comparison can never be true. Anybody got an idea what to do? PS: Getting the address of the native function like this works: path ("d:\hello\hell", reinterpret_cast<boost::filesystem::path::name_check> (GetProcAddress (GetModuleHandle("boost_filesystem-vc71-mt-gd-1_31"), "?native@filesystem@boost@@YA_NABV?$basic_string@DU?$char_traits@D@std@@ V?$allocator@D@2@@std@@@Z"))); But is not really an option... -- Christian Hoffmann This message, including any attachments, is intended only for the person(s) to whom it is addressed. If you received it in error, please let us know and delete the message from your system. This message may be confidential and may fall under the duty of non-disclosure. Any use by others than the intended addressee is prohibited. Trema shall not be liable for any damage related to the electronic transmission of this message, such as failure or delay of its delivery, interception or manipulation by third parties, or transmission of viruses or other malicious code.

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How to install boost step by step approach
by sena 21 Jul '04

21 Jul '04

Hi Friends, I am trying to use Bayer++ classes for Kalman filter But before that I have to install boost c++ library. My fisrt effort was not successful. Can anyone tell me how to install it in Redhat Linux-8? I need step by step with best bug free versions Thanks a lot Sena Seneviratene Computer Engineering Lab Sydney University Australia

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Regex Problems
by Pietje Leugenaar 21 Jul '04

21 Jul '04

Hi, compiling "a{7}" or any repeat with curly brackets gives me an "invalid regex synyax"! Any clues or workarounds? Then boost::regex expression("GO:(\d+)",regex::bk_refs); string str=boost::regex_replace("GO:000015|GO:00016",expression,"$1") str equals "00001500015|00016" instead of the expected "000015|00016"!? I constructed a workaround for the latter problem with an explicit loop over regex_iterator and such but this not really handy... Thanx for any feedback!! Kenny _________________________________________________________________ Plannen om een nieuwe computer te kopen? Kijk eens hier.. http://www.msn.be/shopping/dell_bis/

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database lib
by Chris 21 Jul '04

21 Jul '04

Hi all, I am wondering if there are any plans to include a database library, for example for ODBC in the boost library. Please bear in mind that I am new to the boost libraries and find them really cool. But like the socket library I found it because of an old post, so that is why I am asking about the database library. Also I found this library really interesting and am using it in a couple of small spike solutions: http://dtemplatelib.sourceforge.net/index.htm (Any comments on the library are welcome) Thanks, Chris

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View the shortest paths
by Daniele Carlucci 20 Jul '04

20 Jul '04

Hi, Which is the command to visualize a path in a graph? For ie I want to visualize all the shortest path inside a graph, or all the path from a source to a dest. Thanks Daniele

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Info about a graph with structure instead node
by Daniele Carlucci 20 Jul '04

20 Jul '04

Hi all, I'm a newby in this library. I'm interested to make a graph of network. It's possible or is very hard to make? I want to have inside every node a struct. Thanks Daniele

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Problems with building filesystem under win32 using vc6 and stlport
by huangliang 20 Jul '04

20 Jul '04

Recently I begin to use stlport in my programs, and I build boost filesystem under win32 using bjam, vc6 and stlport 5.0. But when I linke to the libfilesystem.lib, the error said that that the libsystem.lib doesn't consist of interfaces that have parameters of _STL::string type. I guess I must have not correctly configure the bjam to build filesystem. But how can I make it to recognize _STL namespace?

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using DFS visitors
by Gustavo Sÿffffe1nchez 20 Jul '04

20 Jul '04

hello all, we are trying to use a DFS visitor in a similar way as the BFS visitor which is used in the example "bfs.cpp" (boost 1.31.0), that is the code, but it complains about a lot of errors in the internal boost library files... #include <boost/config.hpp> #include <assert.h> #include <vector> #include <algorithm> #include <utility> #include <iostream> #include <boost/graph/adjacency_list.hpp> #include <boost/graph/depth_first_search.hpp> #include <boost/graph/visitors.hpp> #include <boost/property_map.hpp> #include <boost/graph/graph_utility.hpp> using namespace boost; using namespace std; // visitor que muestra el orden en que se encuentran los arcos template <class NewGraph, class Tag> struct muestra_orden : public boost::base_visitor<muestra_orden<NewGraph, Tag> > { typedef Tag event_filter; muestra_orden(NewGraph& graph) : new_g(graph) { } template <class Edge, class Graph> void operator()(Edge e, Graph& g) { cout << "arco: " << e << endl; } private: NewGraph& new_g; }; template <class NewGraph, class Tag> inline muestra_orden<NewGraph, Tag> MuestraOrden(NewGraph& g, Tag) { return muestra_orden<NewGraph, Tag>(g); } //**************************************************************************+ template <class NewGraph, class Tag> struct muestra_ordenV : public boost::base_visitor<muestra_ordenV<NewGraph, Tag> > { typedef Tag event_filter; muestra_ordenV(NewGraph& graph) : new_g(graph) { } template <class Vertex, class Graph> void operator()(Vertex v, Graph& g) { cout << "ARCO: " << v << endl; } private: NewGraph& new_g; }; template <class NewGraph, class Tag> inline muestra_ordenV<NewGraph, Tag> MuestraOrdenV(NewGraph& g, Tag) { return muestra_ordenV<NewGraph, Tag>(g); } /********************************************************/ int main(int , char* []) { using namespace boost; typedef boost::adjacency_list< boost::mapS, boost::vecS, boost::undirectedS, boost::property<boost::vertex_color_t, boost::default_color_type, boost::property<boost::vertex_degree_t, int, boost::property<boost::vertex_in_degree_t, int, boost::property<boost::vertex_out_degree_t, int> > > > > Graph; Graph G(11); boost::add_edge(5, 6, G); boost::add_edge(0, 1, G); // 0 es el + boost::add_edge(1, 2, G); boost::add_edge(1, 3, G); boost::add_edge(2, 4, G); boost::add_edge(3, 5, G); boost::add_edge(4, 6, G); boost::add_edge(5, 7, G); // 7 es el - boost::add_edge(5, 10, G); boost::add_edge(10, 11, G); boost::add_edge(11, 12, G); typedef graph_traits<Graph>::vertex_descriptor Vertex; typedef graph_traits<Graph>::vertices_size_type size_type; Graph G_copy(11); size_type d[11]; std::vector<Vertex> p(num_vertices(G)); std::fill_n(d,11,0); Vertex s=7; p[s]=s; boost::depth_first_search (G, visitor(boost::make_dfs_visitor( std::make_pair(boost::record_predecessors(&p[0],boost::on_tree_edge()), std::make_pair(MuestraOrdenV(G_copy,boost::on_finish_vertex()), MuestraOrden(G_copy, boost::on_tree_edge())))) ), s); // we can compile the visitor(...) clause alone, but not inside depth_first_search (...) clause. return 0; } thanks a lot Gus --------------------------------- [input] [input] [input]

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Dependency of Boost library on STD namespace
by anas munir 19 Jul '04

19 Jul '04

Dear users, I am trying to port Boost Library with Microtec Toolkit. Is it possible to build Boost Library without Standard C++ RTL placed in std namespace ? If yes, then please guide me to the mechanism to do so. Like in STLport, this thing is configurable. Regards, Anas

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Re: [Boost-users] serialization of a complex object
by Bo Peng 19 Jul '04

19 Jul '04

On Mon, Jul 19, 2004 at 05:08:02AM -0700, Jeff Garland wrote: > There are still some open issues with getting all the serialization tests > working. Thanks. I should have checked this before I used the library.... this cost me several hours of painful debugging. :-( Bo

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serialization of a complex object
by Bo Peng 19 Jul '04

19 Jul '04

Dear list, I have tried many ways but could not figure out how to boost::serialize the following object: Basically, to maintain a big chunk of small objects, I use a memory pool to allocate a big trunk of memory and return the pointers to small objects. struct small { int size; int * ptr; init(int s, int* p){ size = s; ptr = p; } } struct All { vector<int> data; vector<small> objs; All(int num_obj, int size_obj) { data.resize( num_obj * size_obj); for(int i=0; i<num_obj; i++) objs[i].init( size_obj, &data[i* size_obj]); } } It is easy to serialize All::data but how to deal with small::ptr is beyond me. I tried the following ways: 1. in small ar & size & ptr. --- template expansion error. 2. in small ar & size & reinterpret_cast<unsigned int>ptr --- core dump. What I am trying to do in 2 is that in load(....), I want to ar & objs; /// get the number of old pointer back. find the smallest number of objs[i].ptr relocate objs[i].ptr to &data[0] + objs[i].ptr - smallest point. However, I can not do this in the load(...) function. The template expansion does not allow changes to objs (this does not make sense to me though). 3. ignore ptr --- can compile, core dump. Can someone give me a bit of insights how I can make things work? Thanks.

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RE: [Boost-users] Re: shared_ptr: LWM versus atomic_count?
by Ben Hutchings 19 Jul '04

19 Jul '04

Russell Hind <rhind(a)mac.com> wrote: > Ben Hutchings wrote: > > > > It isn't fundamentally necessary to have two counters, though; see > > <http://groups.google.com/groups?threadm=slrnbhbnpc.154.do-not-spam > > -benh%40tin.bwsint.com>. > > I'd seen this (I think you posted the same link recently). I don't > know if anything has been done to change the implementation of > shared_ptr to use this method, though (nothing to do with me). The difficulty is that it depends on a couple of unportable atomic functions that can't be implemented using the existing contents of Boost.Threads or pthreads (though they do translate neatly into Win32 functions). > If the speed increases mentioned are correct, then it certinaly > seems a good proposal. Well maybe I'll have a go at implementing it properly and then trying to get it into Boost. I suppose it can be selectively enabled for those platforms that support it.

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Re: Building boost under mingw: bjam invokes VC7?? (part IV: solu tion)
by Brewer, Christopher 19 Jul '04

19 Jul '04

I have found my way around the problem, though I don't understand why it works. Recap of the problem (for those joining late): attempting to build boost with bjam under msys/mingw resulted in very strange behavior. Within the msys shell, invoking the following line: bjam -sTOOL=mingw install ...resulted in bjam attempting to use the VC7 toolset. I checked the path within msys to make sure I was running the version of bjam.exe that I thought I was. Looking through the directories showed there was indeed only one copy. On a hunch, I moved it from it's present location at 'c:/msys/1.0/bin' to 'c:/msys/1.0/mingw/bin' and tried again. And suddenly bjam began using gcc. 8^0 Apparently where you run it from makes a big difference. I'm sure that an msys guru could take one look at the symptoms and say, "Of course! It's obvious to the meanest intellect!". Not being an msys guru I will just shrug my shoulders and move forward :) All is well now and Boost is building even as I type this message. Many thanks to those who replied! Best regards, Chris Brewer (Company-mandated disclaimer) This message originates from WMS Gaming Inc. It contains information which may be confidential or privileged and is intended only for the individual or entity named above. It is prohibited for anyone else to disclose, copy, distribute or use the contents of this message. All personal messages express views solely of the sender, which are not to be attributed to WMS Gaming Inc., and may not be copied or distributed without this disclaimer. If you received this message in error, please notify us immediately at (847) 785-3000.

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Re: [Boost-users] Installation of boost-sandbox
by Ross Boylan 18 Jul '04

18 Jul '04

On Sun, Jul 18, 2004 at 01:56:20AM -0400, Franz Mueller wrote: > Hi, > I've heared of the ublas-binding to lapack, which sounds very good. > Thus I tried to install it, but I didn't succeed. > I got boost-sandbox using cvs. Then I went to the boost-sandbox directory > and did a bjam. > I'd be interested in hearing the answer to this too, as I've been looking in the sandbox. My impression is that it is not meant to be built as a whole. As the name implies, it's a bunch of separate projects, so I think the intent is that you pull one or more of them out and stick them in a regular boost tree. That's just a guess, and I notice that this seems awkward to do since a single project may appear in several scattered directories.

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array_traits?
by Duane Murphy 18 Jul '04

18 Jul '04

Howdy fellow boosters, Several years ago I started using array_traits. I gathered from some later discussion that this library was never meant to be part of boost. However, I really like the library and find it more useful than the array<> implementation. Point in fact, array_traits and array<> overlap but probably weren't meant to solve the same problems [1]. Is array_traits around any more? I seem to recall something more general purpose. Maybe container_traits? Is this still being actively worked on? I am planning on (finally) upgrading our use of boost to a more recent version. I'm trying to work out what to do about our use of array_traits. Maybe I'll just keep using it. ...Duane [1] The primary difference between array_traits and array<> is the "construction" of the array. array_traits in fact has no construction. It can work with any arbitrary defined C-array of objects. array<> on the other hand requires construction. For my use,the major advantage that array_traits has over array<> is that I can refer to any ordinary C- array; in particular arrays that may not be under my control. Where as array<> requires that I change the type of the object.

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