December 2001 - Boost-users

Compose/mem_fun/confusion
by dmoore99atwork 18 Dec '01

18 Dec '01

Hello, I'm trying to explore the compose, bind, and mem_fn libraries. I used a "real" problem I'm having. Given a vector<Trade>, I want to gather a sum of the return values of Trade::volume(). I wound up writing "accumulate_with_op" thusly: template <class _InputIterator, class _Tp, class _UnaryOperation> _Tp accumulate_with_op(_InputIterator first, _InputIterator last, _Tp Init, _UnaryOperation unary_op) { for ( ; first != last; ++first) Init = Init + unary_op(*first); return Init; } And I can call it like this: vector<Trade> li; // ..... sum = accumulate_with_op(li.begin(),li.end(),0,mem_fun_ref (&Trade::volume)) This gives me my sum pretty nicely, so I'm sort of happy... BUT... I tried for a long time to use combinations of for_each, compose_f_gx, and mem_fn to be able to do the Sum (to lead to other things like mean, stddev) into a stateful function object. Something like this: /* broken code, trying to convery my intentions */ MeanValue m1; m1 = for_each(l.begin(), l.end(),compose_f_gx(MeanValue(),mem_fun_ref (&Trade::volume)); cout << m1.result(); I wanted my MeanValue::operator() to be called with the return value from my member function, and I wanted to be able to "capture" the result in a function object i could interrogate afterwards. 1. Am I barking up the wrong tree? accumulate_with_op was pretty easy to write, but my problem seemed straighforward enough to be solved with standard c++ or Boost building blocks. 2. Or I am just using the wrong compiler (MSVC6 SP5)? Thanks, Dave

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Compiler status: win32 question
by kelvinlao 18 Dec '01

18 Dec '01

Does a failure on the Compiler Status chart http://www.boost.org/status/cs-win32.html indicate that a certain compiler cannot use the boost libraries fully? Take for instance, the failure of Visual C++ reported against libs/concept_check/class_concept_fail_expected.cpp: What exactly does this failure mean to a user of the boost libraries? Does it render the boost library or some portion therein unusable by the VC++ programmer? Thanks! -k

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RE: [Boost-Users] Compose/mem_fun/confusion
by Moore, Dave 18 Dec '01

18 Dec '01

Thanks very much for the informative response. Dave > -----Original Message----- > From: Douglas Gregor [mailto:gregod@cs.rpi.edu] > Sent: Friday, December 14, 2001 4:50 PM > To: Boost-Users(a)yahoogroups.com > Subject: Re: [Boost-Users] Compose/mem_fun/confusion > > > On Friday 14 December 2001 03:06 pm, you wrote: > > Hello, > > > > I'm trying to explore the compose, bind, and mem_fn libraries. I > > used a "real" problem I'm having. Given a vector<Trade>, I want to > > gather a sum of the return values of Trade::volume(). > [...] > > vector<Trade> li; > > // ..... > > sum = accumulate_with_op(li.begin(),li.end(),0,mem_fun_ref > > (&Trade::volume)) > > > > This gives me my sum pretty nicely, so I'm sort of happy... BUT... > > Here are two ways to compute the sum without defining your > own functions or > classes. Both methods use std::accumulate (which, of course, > is what you're > trying to do), but the difference is in the way that > Trade::volume() is > called. > > The first code snippet uses Boost.Bind only. We essentially > create a function > object that takes two arguments, x and y, and then performs > the operation x + > y.Volume(). We get '+' by using the standard library's > plus<int>, and we use > the fact that bind is composable to call Volume on the second > argument. The > code is thus: > > std::accumulate(li.begin(), li.end(), 0, > boost::bind<int>( > std::plus<int>(), > _1, > boost::bind(&Trade::Volume, _2))); > > The other option is philosophically different. Instead of > transforming he > values as we add them, we instead transform the sequence we > are adding using > the Boost Iterator Adaptors library. The transform_iterator adapts an > iterator by applying a function object to each element as it > is dereferenced. > Therefore, the sequence that accumulate "sees" is the result > of calling > Trade::Volume on each member of the underlying sequence. > Here's the code: > > std::accumulate( > boost::make_transform_iterator(li.begin(), > > boost::mem_fn(&Trade::Volume)), > boost::make_transform_iterator(li.end(), > > boost::mem_fn(&Trade::Volume)), > 0); > > I consider this version better (philosphically) because the > accumulation is > over things we can actually accumulate - integers. The > transform_iterator > version is also more reusable code, because now you have the > ability to > transform a sequence of Trade objects (or Trade object > pointers - see the > documentation of mem_fn) into their corresponding trade > volumes, and other > operations become simpler. > > Code was tested under GCC 2.95.3, but I expect it will work for MSVC5. > > Doug > > ------------------------ Yahoo! Groups Sponsor > ---------------------~--> > Unlimited PC-PC calling at Crystal Voice! - Only $1/Mo. > Download your free 30 day trial. Click here. > http://us.click.yahoo.com/Gb1xVB/GxbDAA/ySSFAA/EbFolB/TM > -------------------------------------------------------------- > -------~-> > > Info: <http://www.boost.org> > Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> > Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> > > > Your use of Yahoo! Groups is subject to > http://docs.yahoo.com/info/terms/ > >

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Simple iterator adaptor example
by Duane Murphy 17 Dec '01

17 Dec '01

I have taken a quick look at iterator adaptor and it seems quite powerful. It seems that iterator_adaptor has two uses. First to adapt one iterator to another. It also seems like it should be able to be used as an interface to other information that has container like qualities that needs an iterator. For example files in directory. Does anyone have an example of how to build one of the later? Not specifically an iterator over files, but the general ability to build an iterator from something that's not an iterator? Thanks for the pointers, ..Duane

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RE: [Boost-Users] MSVC6 and tuple
by Tom Matelich 17 Dec '01

17 Dec '01

Yeah, I also avoid any using in any header, but what are you going to do if you can't compile otherwise? > -----Original Message----- > From: Darin Adler [mailto:darin@bentspoon.com] > Sent: Monday, December 17, 2001 2:15 PM > To: Boost-Users(a)yahoogroups.com > Subject: Re: [Boost-Users] MSVC6 and tuple > > > On 12/17/01 12:36 PM, "Tom Matelich" <tmatelich(a)zetec.com> wrote: > > > Any suggestions? > > This may not be what you have in mind, but in my own code I prohibit: > > using namespace boost; > > But in code outside header files, I always use: > > using boost::tuple; > > And the like, except in cases where there are name conflicts. > So I have > includes at the top of my source files, followed by using statements, > followed by code. > > -- Darin > > > ------------------------ Yahoo! Groups Sponsor > ---------------------~--> > Need new boots for winter? Looking for a perfect gift for > your shoe loving friends? > Zappos.com is the perfect fit for all your shoe needs! > http://us.click.yahoo.com/ltdUpD/QrSDAA/ySSFAA/EbFolB/TM > -------------------------------------------------------------- > -------~-> > > Info: <http://www.boost.org> > Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> > Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> > > > Your use of Yahoo! Groups is subject to > http://docs.yahoo.com/info/terms/ > >

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MSVC6 and tuple
by Tom Matelich 17 Dec '01

17 Dec '01

I have a tuple as a member of one of my classes, and it appears, that MSVC 6 requires me to do a using boost::tuple, rather than declaring it with the boost namespace at the var. For this declaration in my header: boost::tuple<int, double> willis; I get the following error: file.h(161) : error C2059: syntax error : '<' file.h(161) : error C2238: unexpected token(s) preceding ';' If I add the using (which I would prefer not to do), the declaration: tuple<int, double> willis; works fine. Any suggestions?

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transitive_closure_test.cpp
by Janos Murvai 17 Dec '01

17 Dec '01

Hi, I compiled this program: transitive_closure_test.cpp with: g++ -ftemplate-depth-30 -I /net/cooler/vol/export/proteome/murvai/CC/BOOST/boost_1_26_0/ transitive_closure_test.cpp then I run: Created graph with 13 vertices. transitive_closure Segmentation fault (core dumped) Exit 139 What can I do in this case? Thank you, Janos

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Why not "if (px != rpx) " ?
by Louis Lavery 17 Dec '01

17 Dec '01

Hello, The following is use by the boost shared_ptr assignment operators (see boost\smart_ptr.hpp)... void share(T* rpx, long* rpn) { if (pn != rpn) { // Q: why not px != rpx? A: fails when both == 0 ++*rpn; // done before dispose() in case rpn transitively // dependent on *this (bug reported by Ken Johnson) dispose(); px = rpx; pn = rpn; } } // share ...I curious to know what it means by "fails when both == 0". I mean, I can't see as the sky would fall in if the test was "if (px != rpx)". Am I missing something? Thanks, Louis.

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preprocessor/min and MSVC
by Rodney.Schuler＠ing-dm.com 14 Dec '01

14 Dec '01

I saw the boost preprocessor library and I thought that BOOST_PREPROCESSOR_MIN might help solve a problem in some code that I am maintaining. This code has the naive implementation of MIN and MAX: #define MIN(a,b) ((a)<(b)?(a):(b)) This code also has many (tens of thousands!) of places where a function calls are used as arguments to MIN and MAX like this: foo=MIN(func(args1),func(args2)) The function called is a very long running function. The performance hit taken by three evaluations of the function is a problem I am working to fix. I know the best solution is to add some local variables, and store the results of the functions in them, then use MIN on the local vars. But I'd like to get some Idea of how much performance increase I am likely to get by crawling through the code and fixing all the occurrences of MIN(func(args1),func(args2)) Wondering if BOOST_PREPROCESSOR_MIN had a way to make only two evaluations of func I wrote: #include <iostream> #include <boost/preprocessor/min.hpp> using std::cout; using std::endl; int func(int i) { cout << " func called " << i << endl; return i; } int main () { cout << "result " << BOOST_PREPROCESSOR_MIN(func(1),func(2)) << "\n" << endl; cout << "result " << BOOST_PREPROCESSOR_MIN(func(4),func(3)) << "\n" << endl; return 0; } And my compilers (MSVC 5 sp3 and MSVC 6 sp5) responded thusly: C:\temp\boostminvc5\main.cpp(15) : error C2065: 'BOOST_PREPROCESSOR_IF_BOOLBOOST_PREPROCESSOR_BOOLBOOST_PREPROCESSOR_IF_BOOLBOOST_PREPROCESSOR_BOOLBOOST_PREPROCESSOR_NOR_BOOLBOOST_PREPROCESSOR_BOOLBOOST_PREPROCESSOR_ADDBOOST_PREPROCESSOR_SUBfunc' : undeclared identifier C:\temp\boostminvc5\main.cpp(15) : error C2065: 'BOOST_PREPROCESSOR_SUBfunc' : undeclared identifier C:\temp\boostminvc5\main.cpp(15) : error C2146: syntax error : missing ';' before identifier 'BOOST_PREPROCESSOR_BOOLBOOST_PREPROCESSOR_ADDBOOST_PREPROCESSOR_SUBfunc' C:\temp\boostminvc5\main.cpp(15) : error C2065: 'BOOST_PREPROCESSOR_BOOLBOOST_PREPROCESSOR_ADDBOOST_PREPROCESSOR_SUBfunc' : undeclared identifier C:\temp\boostminvc5\main.cpp(15) : error C2065: 'BOOST_PREPROCESSOR_NOR_BOOLBOOST_PREPROCESSOR_BOOLBOOST_PREPROCESSOR_SUBfunc' : undeclared identifier C:\temp\boostminvc5\main.cpp(15) : error C2146: syntax error : missing ')' before identifier 'BOOST_PREPROCESSOR_BOOLBOOST_PREPROCESSOR_SUBfunc' C:\temp\boostminvc5\main.cpp(16) : error C2146: syntax error : missing ';' before identifier 'BOOST_PREPROCESSOR_BOOLBOOST_PREPROCESSOR_ADDBOOST_PREPROCESSOR_SUBfunc' C:\temp\boostminvc5\main.cpp(16) : error C2146: syntax error : missing ')' before identifier 'BOOST_PREPROCESSOR_BOOLBOOST_PREPROCESSOR_SUBfunc' First, this is a bug report. Second, can anybody answer my question does BOOST_PREPROCESSOR_MIN get around the unnecessary evaluations problem? Thanks -Rodney Rodney.Schuler(a)ing-dm.com

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run test programs...
by Janos Murvai 13 Dec '01

13 Dec '01

Hi, I'm one new user. I tried to run test programs in the : ..../boost_1_26_0/libs/graph/test When I try to compile: g++ -I /net/cooler/vol/export/proteome/murvai/CC/BOOST/boost_1_26_0/ adj_matrix_cc.cpp I got many error message (some example from the error messages): What can I do in this case? /net/cooler/vol/export/proteome/murvai/CC/BOOST/boost_1_26_0/boost/iterator_adaptors.hpp:817: instantiated from `boost::iterator_adaptor<boost::iterator_adaptor<char *,boost::detail::dir_adj_matrix_out_edge_iter_policies<unsigned int,char *,unsigned int>,boost::detail::matrix_edge_desc_impl<boost::directed_tag,unsigned int>,boost::detail::matrix_edge_desc_impl<boost::directed_tag,unsigned int>,boost::detail::matrix_edge_desc_impl<boost::directed_tag,unsigned int> *,boost::multi_pass_input_iterator_tag,int>,boost::filter_iterator_policies<boost::detail::does_edge_exist,boost::iterator_adaptor<char *,boost::detail::dir_adj_matrix_out_edge_iter_policies<unsigned int,char *,unsigned int>,boost::detail::matrix_edge_desc_impl<boost::directed_tag,unsigned int>,boost::detail::matrix_edge_desc_impl<boost::directed_tag,unsigned int>,boost::detail::matrix_edge_desc_impl<boost::directed_tag,unsigned int> *,boost::multi_pass_input_iterator_tag,int> >,boost::detail::matrix_edge_desc_impl<boost::directed_tag,unsigned int>,boost::detail::matrix_edge_desc_impl<boost::directed_tag,unsigned int>,boost::detail::matrix_edge_desc_impl<boost::directed_tag,unsigned int> *,boost::multi_pass_input_iterator_tag,int>' /net/cooler/vol/export/proteome/murvai/CC/BOOST/boost_1_26_0/boost/graph/adjacency_matrix.hpp:326: instantiated from `boost::adjacency_matrix<boost::directedS,boost::no_property,boost::no_property,boost::no_property,allocator<bool> >' /net/cooler/vol/export/proteome/murvai/CC/BOOST/boost_1_26_0/boost/graph/graph_traits.hpp:38: instantiated from `boost::graph_traits<boost::adjacency_matrix<boost::directedS,boost::no_property,boost::no_property,boost::no_property,allocator<bool> > >' /net/cooler/vol/export/proteome/murvai/CC/BOOST/boost_1_26_0/boost/graph/graph_concepts.hpp:177: instantiated from `boost::VertexListGraphConcept<boost::adjacency_matrix<boost::directedS,boost::no_property,boost::no_property,boost::no_property,allocator<bool> > >' /net/cooler/vol/export/proteome/murvai/CC/BOOST/boost_1_26_0/boost/concept_check.hpp:41: instantiated from `boost::function_requires<boost::VertexListGraphConcept<boost::adjacency_matrix<boost::directedS,boost::no_property,boost::no_property,boost::no_property,allocator<bool> > > >()' adj_matrix_cc.cpp:35: instantiated from here /net/cooler/vol/export/proteome/murvai/CC/BOOST/boost_1_26_0/boost/type_traits/composite_traits.hpp:204: incomplete type `boost::is_member_pointer<char *>' does not have member `value' Thank you, Janos

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