April 2003 - Boost-users - lists.boost.org

RE: [Boost-Users] pool_allocator problems on VC7.1 (real release)
by Ben Hutchings 23 Apr '03

23 Apr '03

John Harris <john.harris(a)tradingtechnologies.com> wrote: > scleary(a)jerviswebb.com wrote: > > John - > > > > Sorry, Boost.Pool does not currently support MSVC, due to that compiler's > > extreme lack of template support. > > > > I also tried this on the real released VC7.1 (which has been on MSDN > subscriber downloads for a couple of weeks, now), and, while it > compiles, I get warnings that point me to some code that looks like > it's losing precision (size_type reduced to bool) in a calculation. VC++ has produced that warning for a while now, and it's totally bogus. Notice that it's a "performance warning" not an "are you sure this is that you want?" warning, and it's being generated here for *casts* not implicit conversions. <snip> > Another test I tried was a map<string,string>, actually declared like > this: > > typedef > std::basic_string<char,std::char_traits<char>,boost::pool_allocator<ch > ar> > t; > std::map<t, t, std::less<t>, boost::pool_allocator<std::pair<const t, > t> > > m; > > ...and got these errors: <snip> I compiled almost the exact same code: #include <boost/pool/pool_alloc.hpp> #include <map> #include <utility> typedef std::basic_string<char,std::char_traits<char>,boost::pool_allocator<char > > t; int main() { std::map<t, t, std::less<t>, boost::pool_allocator<std::pair<const t, t> > > m; } with VC++ 7.0 and Boost 1.29, and got no warnings or errors at all. The command line was: cl /D__WIN32__ /EHsc /I"c:\program files\boost" test.cpp I repeated this with Boost 1.30 and again got no warnings or errors. I don't have VC++ 7.1 to hand, but I would be surprised if it broke anything that worked in 7.0.

2 1

Signal/Slot copy semantics.
by Jesper Bojesen 23 Apr '03

23 Apr '03

I have a problem with the sematics of the the signal connect method. Consider this simple program: #include <iostream> #include <boost/signal.hpp> struct HelloWorld { void operator()() const { std::cout << "Hello, World!, the parallel world exist at " << (void *) this << std::endl; } }; int main () { // Connect a HelloWorld slot HelloWorld hello; std::cout << "Main world at " << (void *) &hello << std::endl; boost::signal<void ()> sig; sig.connect(hello); sig (); std::cout << "Thats all folks!\n"; return 0; } It produces this output: >Main world at 0xbffff2e0 >Hello, World!, the parallel world exist at 0x8056128 >Thats all folks! My problem is that the object signalled is not the same object that I subscribed to the signal. Is this really what was inteded ? Is the any rationale behind this behaviour ? -- Jesper Bojesen Medical Insight Email: jbb(a)medical-insight.com Phone mobile: (+45) 40 99 55 03 Phone direct: (+45) 46 55 04 42 Fax: (+45) 46 55 11 66

3 5

UBLAS and algorithms
by David Johnson 23 Apr '03

23 Apr '03

Hi, I'm looking to solve some matrix problems using conjugate gradient methods. CGS and GMRES to name a couple. I see where the matricies can be stored by the UBLAS classes, but I don't see any of the algorithms available in boost. Are they available somewhere? I've looked at packages like IML++ and see them there, but they appear to use different storage classes. Can anyone point me in the direction of where some boost compatible algorithms are? Thanks, Dave

1 0

RE: pool_allocator problems on VC7.1 (real release)
by scleary＠jerviswebb.com 23 Apr '03

23 Apr '03

> -----Original Message----- > From: John Harris [mailto:john.harris@tradingtechnologies.com] > I also tried this on the real released VC7.1 (which has been on MSDN > subscriber downloads for a couple of weeks, now), and, while it > compiles, I get warnings that point me to some code that looks like > it's losing precision (size_type reduced to bool) in a calculation. > The pool code about which the following warnings complain: > > const size_type num_chunks = total_req_size / partition_size + > static_cast<bool>(total_req_size % partition_size); > The cast is intentional. The intent is to add one if the result of the modulus is non-zero. I don't know why the compiler is producing warnings, since I'm using an explicit cast. > Another test I tried was a map<string,string>, actually declared like > this: I'm having a hard time deciphering the compiler errors (I'm not used to MSVC errors), but it looks like it might be a problem in the STL. Have you tried this with STLPort? > If you have an example of a map<string,string> using pool_allocator > that compiles on VC7.1, I'd *love* to see it. That's all I'm really > after, here. Is MSVC available for download for non-MSDN subscribers? If so, I can download it and try to get it working. -Steve

2 1

Trouble grokking iterator adaptors
by Kris Braun 23 Apr '03

23 Apr '03

Hi there, I could really use the features provided by iterator adaptors part of the library, but I'm having a lot of trouble getting a nested set of adaptors to compile. In one case, I'd like to return an iterator into std::map< std::string, boost::shared_ptr< ApiOption > >, and have it return references to options in which option->isTemplate( ) is false. Conceptually, I'd like a filter_iterator->indirect_iterator- >projection_iterator chain. I've been using this typedef to project onto the second member of the pair: typedef boost::projection_iterator_pair_generator< select_second< std::string, boost::shared_ptr< ApiOption > >, OptionMap::iterator, OptionMap::const_iterator > OptionMapIterators; but I've been at a loss to add indirect_iterator and filter_iterator into the mix. Can anyone help me get unstuck? Thank you in advance, Kris

5 7

RE: [Boost-Users] simplest pool_alloc example does not work on VC 6
by scleary＠jerviswebb.com 23 Apr '03

23 Apr '03

John - Sorry, Boost.Pool does not currently support MSVC, due to that compiler's extreme lack of template support. -Steve > -----Original Message----- > From: John Harris [mailto:john.harris@tradingtechnologies.com] > > Using Boost 1.30.0. MSVC6 > Tow problems: (1) I have to #define __WIN32__, and (2) Doesn't compile

3 2

The unholy triumvirate of Boost, MacOS X & gcc
by Paul-Michael Agapow 23 Apr '03

23 Apr '03

Does any one have recent experience with compiling / installing Boost on a Mac using gcc? A brief vox-poll seems to say that most everyone on the Mac uses it with CodeWarrior, manually including it in their project. However I'm more interested in using gcc / ProjectBuilder, and distributing the source code to my programs. So, I need to know if my end-users are going to have any problems installing Boost? My attempts have been been discouraging. The first install of Spirit almost immediately consumed all the memory on my machine and thrashed. Installation of the full Boost failed with link errors reporting "unrecognised option shared". Editing this option out of the regex makefile, lead to the next problem, failures with the unittests. Suspecting I was missing something obvious, I handed the problem over to someone else who spend a few days following the same trail, eventually commenting out the unittests. Sure, I could include the boost source with every program I use it in, but this strikes me as untidy and means every time Boost updates, I have to update the x separate copies on my disk. Opinions or sympathies? p -- Dr Paul-Michael Agapow (p.agapow(a)ucl.ac.uk) Dept. Biology, University College London

3 2

Using for_each on a std::list<boost::function0<void> >
by Russell Hind 23 Apr '03

23 Apr '03

I have a std::list of boost::function0<void> I would like to call all items using a for_each statement. Is there a standard function object that I can pass into the for_each call that will call operator() on each element? Thanks Russell

2 2

dijkstra_shortest_paths with undirectedS example
by jfw1000 23 Apr '03

23 Apr '03

Hello, I am new to BGL, I was trying to test dijkstra_shortest_paths() with undirectedS, the result is not what I wanted, anyone giving help? Thanks, source code like dijkstra-example.cpp in the graph/example. int main(int, char *[]) { typedef adjacency_list < listS, vecS, undirectedS, no_property, property < edge_weight_t, double > > graph_t; typedef graph_traits < graph_t >::vertex_descriptor vertex_descriptor; typedef graph_traits < graph_t >::edge_descriptor edge_descriptor; typedef std::pair<int, int> Edge; const int num_nodes = 3; Edge edge_array[] = { Edge(0, 1),Edge(1, 2), Edge(2, 0) }; double weights[] = {2.0, 1.0, 1.0}; int num_arcs = sizeof(edge_array) / sizeof(Edge);// #if defined(BOOST_MSVC) && BOOST_MSVC <= 1300 graph_t g(num_nodes); property_map<graph_t, edge_weight_t>::type weightmap = get (edge_weight, g); for (std::size_t j = 0; j < num_arcs; ++j) { edge_descriptor e; bool inserted; tie(e, inserted) = add_edge(edge_array[j].first, edge_array [j].second, g); weightmap[e] = weights[j]; } #else graph_t g(edge_array, edge_array + num_arcs, weights, num_nodes); property_map<graph_t, edge_weight_t>::type weightmap = get (edge_weight, g); #endif std::vector<vertex_descriptor> pred(num_vertices(g)); std::vector<double> d(num_vertices(g)); vertex_descriptor s = vertex(0, g); #if defined(BOOST_MSVC) && BOOST_MSVC <= 1300 // VC++ has trouble with the named parameters mechanism property_map<graph_t, vertex_index_t>::type indexmap = get (vertex_index, g); dijkstra_shortest_paths(g, s, &pred[0], &d[0], weightmap, indexmap, std::less<double>(), closed_plus<double>(), std::numeric_limits<double>::max(), 0, default_dijkstra_visitor()); #else dijkstra_shortest_paths(g, s, predecessor_map(&p[0]).distance_map(&d [0])); #endif std::cout << "distances and parents:" << std::endl; graph_traits < graph_t >::vertex_iterator vi, vend; for (tie(vi, vend) = vertices(g); vi != vend; ++vi) { std::cout << "distance(" << *vi << ") = " << d[*vi] << ", "; std::cout << "parent(" << *vi << ") = " << pred[*vi] << std::endl; } std::cout << "min paths tree" << std::endl; adjacency_list<> tree(num_nodes); for(tie(vi,vend) = vertices(g); vi != vend; ++vi) if (*vi != pred[*vi]) add_edge(pred[*vi], *vi, tree); print_graph(tree); std::cout << std::endl; return EXIT_SUCCESS; } The result is : distances and parents: distance(0) = 0, parent(0) = 0 distance(1) = 2, parent(1) = 0 distance(0) = 1, parent(2) = 0 min paths tree 0 -> 1 2 1 -> 2 -> I think the correct one should be: distances and parents: distance(0) = 0, parent(0) = 0 distance(1) = 2, parent(1) = 2 distance(2) = 1, parent(2) = 0 min paths tree 0 -> 1 1 -> 2 2 -> Any idea what is wrong? thanks!

3 3

RE: [Boost-Users] simplest pool_alloc example does not work on VC 6
by scleary＠jerviswebb.com 23 Apr '03

23 Apr '03

> -----Original Message----- > From: Ben Hutchings [mailto:ben.hutchings@businesswebsoftware.com] > > scleary(a)jerviswebb.com wrote: > > Sorry, Boost.Pool does not currently support MSVC, due to that > compiler's > > extreme lack of template support. > <snip> > > For VC++ 6, all that should be needed is a _Charalloc function (instead > of struct rebind) and a change to the type of deallocate's first > parameter (to void *, which actually makes more sense). The _Charalloc function requires each allocator to be able to allocate an arbitrary amount of memory. This goes against the entire design of Boost.Pool, and would be non-trivial (to say the least) to implement. > The VC++ 7 compiler is good enough to support standard allocators and > the library does use them. With the addition of a variable name and > semi-colon, the given example can be compiled with this version. Glad to hear it. Too bad it's not released yet. -Steve

2 1

RE: [Boost-Users] Boost::Filesystem: Directory iterator and dangling links
by Ben Hutchings 23 Apr '03

23 Apr '03

You wrote: <snip> > In the case of dangling links I obtain a not_found_error. > This seems to be a contradiction. First I find something (and obtain an > iterator) and without any interference from > outside is_directory() tells me it cannot find the object. > The problem is that directory_iterator refers to the link whereas > is_directory() and the following exception refer to the target (which is > missing). <snip> To make this consistent, then, maybe is_directory() and friends should be using lstat rather than stat on Unix. Is it desirable that links be resolved? I suppose it is if the iterator is being used to walk a whole tree - but not if it's being used to list a single directory. Perhaps there is a need to include explicit support for links in the API. Windows has supported them since 2000, so they aren't just a Unix thing now.

2 1

RE: [Boost-Users] simplest pool_alloc example does not work on VC 6
by Beman Dawes 22 Apr '03

22 Apr '03

At 01:40 PM 4/22/2003, scleary(a)jerviswebb.com wrote: >> -----Original Message----- >> From: Ben Hutchings [mailto:ben.hutchings@businesswebsoftware.com] >>... >> The VC++ 7 compiler is good enough to support standard allocators and >> the library does use them. With the addition of a variable name and >> semi-colon, the given example can be compiled with this version. > >Glad to hear it. Too bad it's not released yet. Ben is probably talking about 7.0, which has been released for a year or so. VC++ 7.1 will be released officially Thursday, the 24th, IIRC. Using the VC++ 7.1 final beta, test_pool_alloc is passing OK. --Beman

1 0

RE: [Boost-Users] simplest pool_alloc example does not work on VC6
by Ben Hutchings 22 Apr '03

22 Apr '03

scleary(a)jerviswebb.com wrote: > Ben Hutchings <ben.hutchings(a)businesswebsoftware.com> wrote: > > scleary(a)jerviswebb.com wrote: > > > Sorry, Boost.Pool does not currently support MSVC, due to that compiler's > > > extreme lack of template support. <snip> > > The VC++ 7 compiler is good enough to support standard allocators and > > the library does use them. With the addition of a variable name and > > semi-colon, the given example can be compiled with this version. > > Glad to hear it. Too bad it's not released yet. Where have you been for the last year?

1 0

Newbie boost help needed..
by Bryan Coon 22 Apr '03

22 Apr '03

Hi, I am totally new to boost and just wanted to ask a couple of simple questions... First, I compiled the boost libraries okay with msvc. I updated the include path in my vc++ 6.0, and can include boost files via #include <boost/xxx.hpp>. So far so good! I wanted to try some things out, like boost's mersenne twister random number generator. I first did this: #include <boost/random/mersenn_twister.hpp> And got no errors. Then I read there was a random.hpp for convenience so I changed this to: #include <boost/random.hpp> And received as a reward complaints: d:\dev\devproject\boost_1_30_0\boost\random\uniform_01.hpp(44) : error C2275: 'std::numeric_limits<`template-parameter258'>::is_integer' : illegal use of this type as an expression d:\dev\devproject\boost_1_30_0\boost\random\uniform_01.hpp(95) : see reference to class template instantiation 'boost::uniform_01<UniformRandomNumberGenerator,RealType>' being compiled There were 6 of these errors. What am I doing wrong? Also, is there a way to include the boost libs in vc++ where I get the autocompletion if I use boost:: ? It is very difficult to figure out how the libs are supposed to be used (for me) by looking at example code or the documentation. Autocompletion as if boost were part of my project would be very useful. Thanks, B

1 0

RE: [Boost-Users] simplest pool_alloc example does not work on VC6
by Ben Hutchings 22 Apr '03

22 Apr '03

scleary(a)jerviswebb.com wrote: > Sorry, Boost.Pool does not currently support MSVC, due to that compiler's > extreme lack of template support. <snip> For VC++ 6, all that should be needed is a _Charalloc function (instead of struct rebind) and a change to the type of deallocate's first parameter (to void *, which actually makes more sense). The VC++ 7 compiler is good enough to support standard allocators and the library does use them. With the addition of a variable name and semi-colon, the given example can be compiled with this version. Is there some other reason why VC++ cannot be supported?

1 0

simplest pool_alloc example does not work on VC6
by John Harris 22 Apr '03

22 Apr '03

Using Boost 1.30.0. MSVC6 Tow problems: (1) I have to #define __WIN32__, and (2) Doesn't compile Am I doing something wrong, here? #include "afxwin.h" #include <map> #define __WIN32__ // why do I have to define this??? #include "boost/pool/pool_alloc.hpp" int main() { std::map<int,int,std::less<int>, boost::pool_allocator<int> > return 0; } :\Program Files\Microsoft Visual Studio\VC98\INCLUDE\xtree(587) : error C2664: 'deallocate' : cannot convert parameter 1 from 'struct std::_Tree<int,struct std::pair<int const ,int>,struct std::map<int,int,struct std::less<int>,class boost::pool_al locator<int,struct boost::default_user_allocator_new_delete,class boost::details::pool::win32_mutex,32> >::_Kfn,struct std::less<int>,class boost::pool_allocator<int,struct boost::default_user_allocator_new_delete,class boost::details::pool::win32_m utex,32> >::_Node *' to 'int *const ' Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\xtree (587) : while compiling class-template member function 'void __thiscall std::_Tree<int,struct std::pair<int const ,int>,struct std::map<int,int,struct std::less<int>,class boost::poo l_allocator<int,struct boost::default_user_allocator_new_delete,class boost::details::pool::win32_mutex,32> >::_Kfn,struct std::less<int>,class boost::pool_allocator<int,struct boost::default_user_allocator_new_delete,class boost::details::pool::win 32_mutex,32> >::_Freenode(struct std::_Tree<int,struct std::pair<int const ,int>,struct std::map<int,int,struct std::less<int>,class boost::pool_allocator<int,struct boost::default_user_allocator_new_delete,class boost::details::pool::win32_mutex,32 > >::_Kfn,struct std::less<int>,class boost::pool_allocator<int,struct boost::default_user_allocator_new_delete,class boost::details::pool::win32_mutex,32> >::_Node *)'

1 0

boost::thread warnings?
by olexander_shyrokov 21 Apr '03

21 Apr '03

I got some warnings when compiling my program (see below). I am using Visual Studio C++ 6 and STLport 4.5.3 I've seen some questions about this issue in the mailing list, but did not get the feeling that I understand what is going on and when I can safly ignore them? Thanks a lot. c:\src\boost\boost\thread\exceptions.hpp(29) : warning C4275: non dll-interface class '_STL::logic_error' used as base for dll-interface class 'boost::lock_error' c:\progra~1\micros~3\vc98\include\stlport\stdexcept(72) : see declaration of 'logic_error' c:\src\boost\boost\thread\exceptions.hpp(35) : warning C4275: non dll-interface class '_STL::runtime_error' used as base for dll-interface class 'boost::thread_resource_error' c:\progra~1\micros~3\vc98\include\stlport\stdexcept(80) : see declaration of 'runtime_error' c:\src\boost\boost\thread\mutex.hpp(37) : warning C4275: non dll-interface class 'boost::noncopyable' used as base for dll-interface class 'boost::mutex' c:\src\boost\boost\noncopyable.hpp(22) : see declaration of 'noncopyable' c:\src\boost\boost\thread\mutex.hpp(75) : warning C4275: non dll-interface class 'boost::noncopyable' used as base for dll-interface class 'boost::try_mutex' c:\src\boost\boost\noncopyable.hpp(22) : see declaration of 'noncopyable' c:\src\boost\boost\thread\mutex.hpp(115) : warning C4275: non dll-interface class 'boost::noncopyable' used as base for dll-interface class 'boost::timed_mutex' c:\src\boost\boost\noncopyable.hpp(22) : see declaration of 'noncopyable' c:\src\boost\boost\thread\thread.hpp(39) : warning C4275: non dll-interface class 'boost::noncopyable' used as base for dll-interface class 'boost::thread' c:\src\boost\boost\noncopyable.hpp(22) : see declaration of 'noncopyable' c:\src\boost\boost\thread\thread.hpp(68) : warning C4275: non dll-interface class 'boost::noncopyable' used as base for dll-interface class 'boost::thread_group' c:\src\boost\boost\noncopyable.hpp(22) : see declaration of 'noncopyable' c:\src\boost\boost\thread\thread.hpp(79) : warning C4251: 'm_threads' : class '_STL::list<class boost::thread *,class _STL::allocator<class boost::thread *> >' needs to have dll-interface to be used by clients of class 'boost::thread_group'

1 0

Problems linking with Boost 1.29.0 thread lib, Linux/g++ 3.2.2 -r2
by subsample 21 Apr '03

21 Apr '03

Failing to link a program with libboost_thread, even though I supply the -lboost_thread directive in the makefile. I'm kind of new to makefiles, having only used Visual C++ in Windows untill recently. I 've tried changing things around a bit, doesn't help. A minimal test program I wrote links fine with boost_thread though. My makefile looks like this: CC=g++ CFLAGS=-g LDFLAGS=-L/home/sub/Libs/alsa/lib -lasound -lboost_thread -lpthread alsatest: alsatest.o $(CC) $(LDFLAGS) -o alsatest SmallObj.o alsatest.o alsatest.o: smallobj.o $(CC) $(CFLAGS) alsatest.cpp -c smallobj.o: $(CC) $(CFLAGS) /usr/include/loki/SmallObj.cpp -c clean: rm -f *.o alsatest g++ complains about the same missing references no matter if I include the -lboost_thread or not. If someone could point out what I'm doing wrong I'd be grateful : )

1 1

Typo in boost/config/compiler/visualc.hpp
by Vaclav Vesely 19 Apr '03

19 Apr '03

line 26: #if (_MSC_VER <= 1300) // 1200 == VC++ 7.0 The comment is inconsistent with the code. Regards, w

2 1

RE: [Boost-Users] lexical_cast regression
by Tom Matelich 18 Apr '03

18 Apr '03

> From: Terje Slettebø [mailto:tslettebo@chello.no] > > >From: "Tom Matelich" <tmatelich(a)zetec.com> > > > I haven't gone and looked at the boost ml archives to track > > the reason for > > this down, but the addition of stream.unsetf(std::ios::skipws) in > > lexical_cast caused some of our code to fail. I've commented it out > > locally, and was wondering why it was decided this is more > > appropriate default behavior. > > It was done to avoid the problems with throwing exceptions on > whitespace. > For example, without it, the following would throw a bad_lexical_cast: > > lexical_cast<std::string>(' '); // A space character > > What kind of code is the current version failing at? > We have some legacy files that are converted to xml through some process (I didn't write it) and it ends up with space-padded strings for ints. So the test case was dying converting " 86" to an int. I can see its purpose, except that example wouldn't happen because of the std::string overload, right? Tom ----------------------------------------------------------------------- DISCLAIMER: Information contained in this message and/or attachment(s) may contain confidential information of Zetec, Inc. If you have received this transmission in error, please notify the sender by return email. -----------------------------------------------------------------------

2 1

Re: [boost] lexical_cast problem
by Terje Slettebø 18 Apr '03

18 Apr '03

>From: "Terje Slettebø" <tslettebo(a)chello.no> > Hm, just now, I sent a reply to a similar problem report at Boost-Users > list, about why whitespace skipping is turned off in the new lexical_cast > version. It was to avoid having things like "lexical_cast<std::string>(' '); > // Space character" work, which used to throw an exception. I meant it was to avoid having it throw an exception, in other words, to _have_ it work. Terje

1 0

Re: [boost] lexical_cast problem
by Terje Slettebø 18 Apr '03

18 Apr '03

>From: "Vladimir Prus" <ghost(a)cs.msu.su> >Subject: [boost] lexical_cast problem Not again. :) > I've just updated my project to use boost 1.30 and also gcc 3.2 and see > exception which reads: > > bad lexical cast: source type value could not be interpreted as target, > Target=i, Source=Ss Ah, yes, good ol' g++ with its wonderfully descriptive type_info names... ;) > The simple reproduction recipe is: > > #include <boost/lexical_cast.hpp> > #include <string> > > int main() > { > boost::lexical_cast<int>(std::string(" 0")); > } "Houston, we have a problem..." Hm, just now, I sent a reply to a similar problem report at Boost-Users list, about why whitespace skipping is turned off in the new lexical_cast version. It was to avoid having things like "lexical_cast<std::string>(' '); // Space character" work, which used to throw an exception. However, it seems this change has had undesired side-effects, in that code like the above now fails to work. Frankly, I don't know what to do with this... > Note the space in string. The exception does not occur with gcc 2.95, but only > with 3.2. I wonder if this should/can be fixed? Personally, I'd expect this > code to work. > > And a related note: the exception's what() above is not quite helpfull. The current version in the CVS has got a changed exception handling, where bad_lexical_cast now looks like this: class bad_lexical_cast : public std::bad_cast { public: // ... const std::type_info &source_type() const const std::type_info &target_type() const virtual const char *what() const throw() { return "bad lexical cast: " "source type value could not be interpreted as target"; } }; In other words, what() now returns the original text, and the type_info objects for the types used is now returned by member functions. > Is it > possible to output the stringstream content (if source -> stringstream > conversion was successfull?) Yes, that's possible. I guess I'll leave it to Kevlin to comment on this. Thanks for the report, to both you and Tom Matelich at Boost-Users list. Regards, Terje

1 0

lexical_cast regression
by Tom Matelich 18 Apr '03

18 Apr '03

I haven't gone and looked at the boost ml archives to track the reason for this down, but the addition of stream.unsetf(std::ios::skipws) in lexical_cast caused some of our code to fail. I've commented it out locally, and was wondering why it was decided this is more appropriate default behavior. Thanks, Tom ----------------------------------------------------------------------- DISCLAIMER: Information contained in this message and/or attachment(s) may contain confidential information of Zetec, Inc. If you have received this transmission in error, please notify the sender by return email. -----------------------------------------------------------------------

2 1

kinda, sorta, like an iterator for dynamic_bitset, but not really.
by Andy Klapper 18 Apr '03

18 Apr '03

I'm currently writing some code for a client where I make extensive use of dynamic_bitsets to determine very quickly which options are appropriate based on a number of criteria. I set up before hand dynamic_bitset for each person, place, and thing which are then bitwise AND'd together to determine where the points of intersection are. What I need is something with an iterator syntax that returns the indexes whose values are set. I could of course just loop through looking for set values, but that seems silly when you think that entire blocks of bits can be skipped if the block has a value of zero. So my questions is, before I set out to write some code, has somebody already done this? It seems like a logical use of dynamic_bit set so it does not seem implausible. If not, any suggestions or warnings? Thanks, Andy

2 1

Understanding MPL
by Edward Diener 18 Apr '03

18 Apr '03

I am trying to understand how the MPL library works. I first read "The Boost C++ Metaprogramming Library" by Aleksey Gurtovoy and David Abrahams. When I get to Basic Usage I see this: template< typename Condition , typename T1 , typename T2 > struct if_ { typedef /*unspecified*/ type; }; I am really having trouble understanding the next to last line. How can "typedef type;" be a valid C++ construct and, if it is, what does it mean ? I always though that a typedef must specify an actual type but I don't see any in the expression above.

7 27