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[Iterators] How to implement proxy iterators?
by Oswin Krause 26 Feb '12

26 Feb '12

Hi Everybody, I'm trying to implement a proxy_iterator for ublas::matrix which should behave as an iterator over the matrix rows. My "obvious" solution does not seem to work: typedef boost::numeric::ublas::matrix<double> Matrix; typedef boost::numeric::ublas::matrix_row<Matrix> MatrixRow; typedef boost::numeric::ublas::vector<double> Vector; struct MatrixIterator: public boost::iterator_facade< MatrixIterator, Vector,//the semantic value type is a Vector boost::random_access_traversal_tag, MatrixRow//reference is a row of a matrix >{ //snip constructors private: friend class boost::iterator_core_access; //snip iterating stuff //fun part MatrixRow dereference() const { return row(*m_matrix,m_element); } std::size_t m_element; Matrix* m_matrix; }; which reuslts in an error that MatrixRow can't be implicitely casted to Vector. Which is correct. At the moment I'm using a 90% hacked workaround which changes the ValueType of the Iterator to MatrixRow. This seems to work as long as I don't use algorithms which rely on the actual value_type of the iterator (for example iter_swap as implemented in the gnu libstdc++ will fail miserably even though a correct swap is implemented for the MatrixRow...different story ) Since I need std::random_shuffle I am out of luck. I tried to find the actual requirements of iterator_facade with respect to ValueType/ReferenceType in the documentation, but was not able to find them. Does someone now a solution to this problem which works and results in an iterator which can safely be used in random_shuffle? Or can point me to the correct requirements? Greetings from Germany, Oswin Krause

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Linking problem
by Johan Råde 26 Feb '12

26 Feb '12

I built Boost with the command b2 toolset=msvc-10.0 address-model=32 link=static runtime-link=shared threading=multi stage I'm linking statically with Boost and dynamically with the CRT (compiler option /MD). I get the error message LINK : fatal error LNK1104: cannot open file 'libboost_iostreams-vc100-mt-1_49.lib' What might the problem be?

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any progress on the logger?
by Victor Whiskey Yankee 25 Feb '12

25 Feb '12

Hello, Any progress on getting the logger into an official release? Thanks, Vic

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[phoenix] Extending actors
by paul Fultz 25 Feb '12

25 Feb '12

Hi all, I am wanting to extend actors to access a member variable from the class. In the examples they show extending an acotr by using a lazy function to call the function. I was thinking I could use a lazy function to access the member, something like this: template <typename Expr> struct point_actor : actor<Expr> { typedef actor<Expr> base_type; typedef point_actor<Expr> that_type; point_actor( base_type const& base ) : base_type( base ) {} typename expression::function<x_impl, that_type>::type x; typename expression::function<y_impl, that_type>::type y; }; Where x_impl and y_impl are lazy functions that access the x and y variable. Would this work as member variables, rather than member functions? Also, why wouldnt the second parameter to expression::function take just actor instead of just point_actor<Expr>? Does that make sense? The reason I ask is I would like to control the actor that is returned and do something like this(using the above actor): template <typename Expr> struct rect_actor : actor<Expr> { typedef actor<Expr> base_type; typedef rect_actor<Expr> that_type; rect_actor( base_type const& base ) : base_type( base ) {} typename expression::function<top_impl, point_actor >::type top; typename expression::function<bottom_impl, point_actor >::type bottom; }; expression::terminal<phoenix::argument<1>, rect_actor > arg1; (cout << arg1.top.x)(my_rect()); Does that make sense? I can't seem to find any reference on the predefined expressions, and I also can't find the header file for expression::function. Finally, the is_actor trait doesn't seem work for extended actors.Is there a workaround for that? Thanks, Paul

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Boost 1.49.0 release notice
by Beman Dawes 24 Feb '12

24 Feb '12

Release 1.49.0 of the Boost C++ Libraries is now available. These open-source libraries work well with the C++ Standard Library, and are usable across a broad spectrum of applications. The Boost license encourages both commercial and non-commercial use. This release contains one new library (Heap) and numerous enhancements and bug fixes for existing libraries. For details, including download links, see http://www.boost.org/users/news/version_1_49_0 You can also download directly from SourceForge: http://sourceforge.net/projects/boost/files/boost/1.49.0/ To install this release on your system, see http://www.boost.org/doc/libs/release/more/getting_started/index.html Thanks, --The Boost release team Beman Dawes Daniel James Eric Niebler Rene Rivera Vladimir Prus

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Detecting file encoding
by norulez＠me.com 24 Feb '12

24 Feb '12

Hi, is there a way in boost to detect the encoding of a file? Thanks in advance Best Regards NoRulez

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iterator_adaptor: making dereference of adapted tree node* return node value
by Rob Desbois 24 Feb '12

24 Feb '12

I have the following iterator_adaptor type: template< class NODE > struct node_iterator: public boost::iterator_adaptor< node_iterator<NODE>, // Derived NODE*, // Base typename NODE::value_type // Value > { typename NODE::value_type dereference() const { return this->base_reference()->data(); } }; // and later: typedef detail::node_iterator<node_type> iterator; typedef detail::node_iterator<const node_type> const_iterator; This throws up the issue that in const_iterator, Value is not const, producing the following error: /usr/include/boost/iterator/iterator_facade.hpp:517:32: error: invalid initialization of non-const reference of type ‘container::detail::node_iterator<const container::detail::node<long unsigned int> >::reference {aka long unsigned int&}’ from an rvalue of type ‘container::detail::node<long unsigned int>::value_type {aka long unsigned int}’ I could do some type traits magic with is_same, is_const and add_const to add the constness to Value if present on NODE, but is this the right way to do it? I've also thought about indirect_iterator - but adding operator*() to the node type seems not quite right. Perhaps transform_iterator...or is there some different method that might be more suitable? TIA, --rob -- Rob Desbois Blog: http://theotherbranch.wordpress.com/ "I disapprove of what you say, but I’ll defend to the death your right to say it", Voltaire

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[posix_time] from_time_t bug
by Matthew Jenks 24 Feb '12

24 Feb '12

Hello, I am running into a problem with boost::posix_time::from_time_t() on a PC with, windows xp, visual studio 2010. When I input a number larger than the decimal equivalent of 0x7FFFFFFF (maximum posssible int32) into the function it returns a ptime with a date of 1902 or something close to. I assume the UNIX equivalent of time_t is a int32 and that is why I am having this problem, but I know a time_t is the equivalent to __int64 in windows xp. Is there is a MACRO define I am missing or is this a bug that needs to be fixed with this function so that it can accept the windows equivalent of time_t? Shouldn't this function accept and convert larger intigers thank int32 to a ptime or do I have to write my own? Thanks, Matt

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Getting Mac address once ip address
by radha bhavani 24 Feb '12

24 Feb '12

Hi, Is there any api available in boost library to get mac addess of the device if ip address is know. Regards, Bhavani

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[MultiIndex] how to rebuild index
by Igor R 24 Feb '12

24 Feb '12

Hello, What's the most simple way to rebuild an index? If elements change without notifying the container, would iterating from begin to end and calling modify() with no-op - do the job? (I remember there already was such a question, but can't find it.) Thanks.

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