September 2008 - Boost-users - lists.preview.boost.org

[timer] eclapsed return zero
by gmail 05 Sep '08

05 Sep '08

3 2

Purpose of identity template
by Annamalai Gurusami 05 Sep '08

05 Sep '08

Hi All, I have been going through the documentation of the multi_index_container in the Boot.MultiIndex library. In the example code provided I saw the use of the identity<> template. The relevant portion of the example code is reproduced here for convenience. http://www.boost.org/doc/libs/1_36_0/libs/multi_index/doc/index.html typedef multi_index_container< employee, indexed_by< // sort by employee::operator< ordered_unique<identity<employee> >, // sort by less<string> on name ordered_non_unique<member<employee,std::string,&employee::name> > > > employee_set; I am trying to understand what is the use of the identity<> template class. I also noticed the following in the documentation, "The predefined identity predicate can be used here as a key extractor; identity returns as the key the same object passed as argument." Is there any reason why the word object (instead of type) is used in that sentence? Also if the identity<> template evaluates to the type given as its argument, is there any benefit out of it? I am quite new to template meta programming and am trying to understand things. Any explanation would be very helpful. Rgds, anna -- Abusive Language on Internet http://missingrainbow.blogspot.com/2008/08/abusive-language-on-internet.html

3 4

Re: [Boost-users] [boost.serialization How does boost.serialization do with BOM
by Tan, Tom (Shanghai) 05 Sep '08

05 Sep '08

Thanks for the quick response. BOM is Windows specific. In my opinion, BOM is not really related to how you encode the text(thus not related to uft_codecvt_facet), but how you mark what your encoding is; so that any text editor can get a prompt of how to handle the text. It's implemented by inserting a few bytes to the very beginning of the file, which are never used in the chosen encoding of the following code. In the case of UTF-8, "EF BB BF" are used -- in the encoding table of UTF-8, "EF BB BF" should correspond to no character(I did not check, just out of guess). As it's related to general text files, not specific to xml files. basic_text_iarchive might be a better place to address the issue. I am thinking just detecting " EF BB BF " and discarding them if they exist would solve the issue. But I am not sure which method need to be overriden, can you please advise? Thanks, tom >This is news to me. >the wide character text/xml archives use UTF-8. They do this >by creating a stream with the uft_codecvt_facet. I used >this factet, it worked great and I moved on. So you're way >ahead of me on this. >This would probably be easy to address in the xml_iarchive code >or perhaps the xml_grammar - but, as I said, I don't know >anything about it. >Robert Ramey Tan, Tom (Shanghai) wrote: >> what is BOM? > >> Probably "Byte Order Mark", see > http://en.wikipedia.org/wiki/Byte-order_mark > > Yes, That's what I meant. > > I was testing the demo_xml_load.cpp and demo_xml_save.cpp available > in the boost.serialization example. > By simply opening demo_save.xml produced by demo_xml_save.exe with XML > copy editor(http://xml-copy-editor.sourceforge.net/) and saving it > back, demo_xml_load.exe would crash. I compared the two files with > Winmerge. It said it's identical. > > by studying the hex view, I later found it's because the 3-byte UTF-8 > BOM was inserted to the beginning of file. It would not change the > data, and in many cases was ignored by the text editors. > > I thinking that Boost.serialization should also handle this for all > text files including XML. > > Tom ------------------------------ _______________________________________________ Boost-users mailing list Boost-users(a)lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users End of Boost-users Digest, Vol 1744, Issue 1 ********************************************

3 2

newbie: initializing a matrix
by Pete 05 Sep '08

05 Sep '08

The examples I've seen construct matrices using for loops, like: matrix<double> m (3, 3); for (unsigned i = 0; i < m.size1 (); ++ i) for (unsigned j = 0; j < m.size2 (); ++ j) m (i, j) = 3 * i + j; but that's inconvenient. I have a matrix in mind, say: double foo[3][3] = { { 1.0, 2.0, 3.0 }, { 2.0, 9.3, 8.1 }, { 3.0, 5.0, 2.3 } }; Is it possible to initialize a matrix<double> from a double[][]? How does one create a matrix without resorting to for loops or via n^2 assignments in the code? Thanks!

1 0

[program_options] Specific sections for options - lack of documentation
by Ken Johnson 05 Sep '08

05 Sep '08

I have absolutely loved the program_options library, and thank those who developed it so well and comprehensive. I love the config file parsing, but am confused on how to implement specific sections. The documentation speaks of parsing through sections of the config file on the following page. Library Overview --> Specific parsers --> Configuration file parser http://www.boost.org/doc/libs/1_36_0/doc/html/program_options/overview.html… However there is no discussion on how to setup some option that is part of a specific section. How can I do this and how will it affect the command line options? I noticed that boost_1_35_0/boost/program_options/detail/config_file.hpp talks about this functionality a little more. I appreciate any help with this, and would especially enjoy code snippets that illustrate creating options that belong to a section.

1 0

[lambda] Making my expression less complicated
by Peter Barker 05 Sep '08

05 Sep '08

Hello, In my test program below, I have a container of columns and want to output the column headers into a string separated by a tab. The lambda expression is looking fairly complicated so I wonder if it could be made simpler or if there's any other algorithm I should've used to put a separator between the elements? Regards, Pete #include <algorithm> #include <iostream> #include <string> #include <vector> #include <boost/lambda/bind.hpp> #include <boost/lambda/lambda.hpp> #include <boost/lambda/if.hpp> class Column { public: explicit Column(const std::string& str) : str_(str) {} const std::string& getColumnText() const {return str_;} private: std::string str_; }; int main() { using namespace boost::lambda; using boost::lambda::_1; std::vector<Column> cols; cols.push_back(Column("Fred")); cols.push_back(Column("Jim")); cols.push_back(Column("Harry")); const std::size_t numCols = static_cast<size_t>(cols.size()); const char fieldSeparator = '\t'; std::string outputText; std::size_t i = 1; var_type<std::size_t>::type iV(var(i)); std::for_each(cols.begin(),cols.end(), ( var(outputText) += bind(&Column::getColumnText,_1), if_then(iV < constant(numCols),var(outputText) += constant(fieldSeparator)), ++iV ) ); std::cout << '[' << outputText << ']'; }

2 2

graph all pair shortest path problem
by Nicolas Heine 05 Sep '08

05 Sep '08

Hi *, I have a question about the All Pair Shortest Path (Johnson) algorithm. Here is my code: #include <boost/config.hpp> #include <fstream> #include <iostream> #include <iomanip> #include <vector> #include <boost/property_map.hpp> #include <boost/graph/adjacency_list.hpp> #include <boost/graph/johnson_all_pairs_shortest.hpp> int main() { using namespace boost; typedef property<vertex_index_t, int, property<vertex_name_t, std::string> > VertexProperty; typedef property<edge_weight_t, int, property<edge_weight2_t, int> > EdgeProperty; typedef property<graph_name_t, std::string> GraphProperty; //adjacency_list<OutEdgeList, VertexList, Directed, // VertexProperties, EdgeProperties, // GraphProperties, EdgeList> typedef adjacency_list<listS, listS, undirectedS, VertexProperty, EdgeProperty, GraphProperty> Graph; boost::graph_traits<Graph>::vertex_descriptor u, v, w, first, second; int N = 10; Graph g; first = add_vertex(g); put(vertex_index, g, first, num_vertices(g)); second = add_vertex(g); put(vertex_index, g, second, num_vertices(g)); add_edge(first, second, g); u = first; v = second; for (int i = 2; i < N; i++) { w = add_vertex(g); put(vertex_index, g, w, i + 1); add_edge(u, w, g); add_edge(v, w, g); u = v; v = w; } add_edge(u, first, g); add_edge(v, second, g), add_edge(v, first, g); std::cout << "Finished to build Graph" << std::endl; //set weights to 1 typedef graph_traits<Graph>::edge_iterator EdgeIterator; EdgeIterator ei, edge_end; for ( boost::tie(ei, edge_end) = edges(g); ei != edge_end; ++ei){ put(edge_weight, g, *ei, 1); } std::vector<int> d(N, (std::numeric_limits<int>::max)()); int D[N][N]; johnson_all_pairs_shortest_paths(g, D, distance_map(&d[0])); std::cout << " "; for (int k = 0; k < N; ++k) std::cout << std::setw(5) << k; std::cout << std::endl; for (int i = 0; i < N; ++i) { std::cout << i << " -> "; for (int j = 0; j < N; ++j) { if (D[i][j] > 20 || D[i][j] < -20) std::cout << std::setw(5) << "inf"; else std::cout << std::setw(5) << D[i][j]; } std::cout << std::endl; } return 0; } When I compile I get the error: ../src/BGLTest.cpp: In function 'int main()': ../src/BGLTest.cpp:73: error: no matching function for call to 'johnson_all_pairs_shortest_paths(main()::Graph&, int [(((long unsigned int)(((int)N) - 1)) + 1u)][(((long unsigned int)(((int)N) - 1)) + 1u)], boost::bgl_named_params<int*, boost::vertex_distance_t, boost::no_property>)' What does that mean? I want to use the Johnson algorithm with a listS = Vertexlist and listS = Egelist. With listS, vecS as in your example it works fine. What can I do? Thanks in advance, Nico

2 1

Closures emulation made easy
by Alexander Gutenev 05 Sep '08

05 Sep '08

Hi. Here's a trick. Use the idea of Boost.ScopeExit. But don't implement capturing of variables like in Boost.ScopeExit - use Boost.Bind which does it. Have easy to write and debug closure body - don't spend too much time on making Boost.Lamda work. And a compact implementation with very small proprocessor overhead, compared to Boost.ScopeExit. // Implementation #define CONCATENATE_DIRECT(s1, s2) s1##s2 #define CONCATENATE(s1, s2) CONCATENATE_DIRECT(s1, s2) #define ANONYMOUS_VARIABLE(str) CONCATENATE(str, __LINE__) #define LOCAL(R, P) \ typedef struct ANONYMOUS_VARIABLE(xg1) { \ typedef R(*F) P; static R body P { #define LOCAL_END(name) \ } } ANONYMOUS_VARIABLE(xg2); \ const ANONYMOUS_VARIABLE(xg2)::F name \ = ANONYMOUS_VARIABLE(xg2)::body; // Example #include <algorithm> int main() { LOCAL(bool, (int i, int j, bool reverse)) return reverse ? (j < i) : (i < j); LOCAL_END(myFcn) int a[] = { 2, 5, 1, 6 }; std::sort( a, a + sizeof(a)/sizeof(a[0]), boost::bind(myFcn, _1, _2, true)); }

2 2

Cannot statically link to Boost.Filesystem
by Graham Bull 05 Sep '08

05 Sep '08

Hi all, I've got this really simple C++ program that's using the Boost.Filesystem library: #include <iostream> #include <boost/filesystem.hpp> int main() { boost::filesystem::path pathname = "/usr/local/bin"; std::cout << pathname.string() << std::endl; return 0; } It compiles fine, and I can get it to link to use the shared object: g++ -I/usr/local/include/boost-1_35 -o test test.cpp -lboost_filesystem-gcc42-mt-1_35 But I want to statically link instead. I've tried this and other similar combinations: g++ -I/usr/local/include/boost-1_35 -o test test.cpp -lboost_filesystem-gcc42-mt-s-1_35 -static -static-libgcc and I'm always getting these linker errors: /tmp/ccoiFv2v.o: In function `__static_initialization_and_destruction_0(int, int)': test.cpp:(.text+0x1dc): undefined reference to `boost::system::get_system_category()' test.cpp:(.text+0x1e6): undefined reference to `boost::system::get_posix_category()' test.cpp:(.text+0x1f0): undefined reference to `boost::system::get_posix_category()' test.cpp:(.text+0x1fa): undefined reference to `boost::system::get_system_category()' collect2: ld returned 1 exit status I've built Boost in full and have got these Boost.Filesystem libraries in /usr/local/lib: libboost_filesystem-gcc42-1_35.a libboost_filesystem-gcc42-1_35.so libboost_filesystem-gcc42-1_35.so.1.35.0 libboost_filesystem-gcc42.a libboost_filesystem-gcc42-d-1_35.a libboost_filesystem-gcc42-d-1_35.so libboost_filesystem-gcc42-d-1_35.so.1.35.0 libboost_filesystem-gcc42-d.a libboost_filesystem-gcc42-d.so libboost_filesystem-gcc42-mt-1_35.a libboost_filesystem-gcc42-mt-1_35.so libboost_filesystem-gcc42-mt-1_35.so.1.35.0 libboost_filesystem-gcc42-mt.a libboost_filesystem-gcc42-mt-d-1_35.a libboost_filesystem-gcc42-mt-d-1_35.so libboost_filesystem-gcc42-mt-d-1_35.so.1.35.0 libboost_filesystem-gcc42-mt-d.a libboost_filesystem-gcc42-mt-d.so libboost_filesystem-gcc42-mt-s-1_35.a libboost_filesystem-gcc42-mt-s.a libboost_filesystem-gcc42-mt-sd-1_35.a libboost_filesystem-gcc42-mt-sd.a libboost_filesystem-gcc42-mt.so libboost_filesystem-gcc42-s-1_35.a libboost_filesystem-gcc42-s.a libboost_filesystem-gcc42-sd-1_35.a libboost_filesystem-gcc42-sd.a libboost_filesystem-gcc42.so I hope someone can help me because I just can't see what I'm doing wrong! Graham

4 9

[review] FSM Library review result
by Martin Vuille 05 Sep '08

05 Sep '08

This is a brief report of the results of the review of Andrey Semashev's Finite State Machines (FSM) library. I want to do justice to the discussions that took place, and will follow-up with a complete summary next week. In spite of a good amount of discussion and an extension of the review period, the number of reviews was smaller than I had hoped for. Nonetheless, I believe that the library received an adequate review and, based on the review comments and other discussions, the FSM library cannot be accepted into Boost at this time. A total of four reviews were submitted, as follows: Andrea Carbone: YES Phil Endecott: NO Jeff Flinn: NO Chris Knight: NO Darryl Green also submitted a mini-review, which did not include an explicit yes or no vote, but expressed doubt about whether the library should be accepted. On the positive side, several people noted that the goals of the library (simplicity and greater performance than Boost.StateCharts) were valid and that such a library was needed in some applications. I personally support this view. I would like to thank Andrey for his efforts in developing the library. I would like to encourage him to pursue the discussions that were begun during this review and perhaps try again with an updated submission. MV

1 0