March 2005 - Boost - lists.preview.boost.org

Interest poll: Define named char/wchar_t string constants in header files
by Alf P. Steinbach 25 Mar '05

25 Mar '05

Following the guidelines for Boost submission at <url: http://www.boost.org/more/submission_process.htm#interest> this is a request for interest. I've posted the file + one little file it depends on at <url: http://groups.yahoo.com/group/boost/files/named_strings/>. This utility lets you use literal strings in char/wchar_t-templated code (and even as template arguments): you can write things such as BOOST_DEF_NAMED_STRING( eq, "=" ) template< typename Char > bool is_assignment_op( std::basic_string<Char> const& s ) { return s == literal::eq::s<Char>(); }

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re: How much should I care about allocators?
by Michael Stevens 24 Mar '05

24 Mar '05

Dan, I looked into allocators last year when implementing uBLAS's storage abstraction using allocators. You should definitely make use of the ISO standard text when working with allocators! On Monday 21 March 2005 04:19, Dan Rosen <dan.rosen(a)gmail.com> wrote: > In other words, to respect the allocator I've been given, I need to > make sure my internal node structure uses the rebound node allocator's > pointer and value types, and so forth. So my first question is, is > this assumption correct? This is correct but requires a lot of library programmer discipline! > The reason I ask is that looking over the > standard library implementation that comes with gcc 4.0, I noticed > that their implementation of std::list<> has nodes which contain > straight pointers, rather than the allocator typedef equivalents. To > me that seems to contradict my assumption, assuming the gcc > implementation is correct. GCC is correct. There is a get out clause in the library standard. Look at section 20.1.5 "Allocator requirements" paragraph 4: Implementations of containers described in this International Standard are permitted to assume that their Allocator template parameter meets the following two additional requirements beyond those in Table 32. All instances of a given allocator type are required to be interchangeable and always compare equal to each other. The typedef members pointer, const_pointer, size_type, and difference_type are required to be T*, T const*, size_t, and ptrdiff_t, respectively. I suspect many implementation (including those not in the standard) have this requirement! > My second question is about allocator's construct() method. The > implementation of std::allocator has construct() invoking the copy > ctor using placement new(). That much is self-explanatory. It also > seems reasonable to me that allocator does not have construct() > methods taking arbitrary parameters. But I'm not sure I understand the > reason why it does not have a construct() method to invoke an object's > default ctor.? In Table 32 "Allocator requirements" construct is specified as a.construct(p,t) Effect: new((void*)p) T(t) >From this I conclude the construct is semantically identical to calling placement new. In effect construct does nothing other then provide a nice bit of syntax. I could just as well use placement new syntax directly or indeed call placement new for any other constructor such as the default constructor. > What that implies to me, and seems to be supported by > gcc's list implementation, is that the nodes in my tree mustn't have a > default ctor that actually does anything, because the only way to > properly initialize objects using an allocator is through copying. Is > that correct I think not. My interpretation is that allocators require that their value_type is Copy Constructable but place no restriction on other ways they may be constructed. That said, STL containers have been carefully designed to avoid the need default construct an object which will be subsequently assigned to. They can keep memory in an uninitialised state until an element is needed and then use copy construction. All the standard containers require their value_type to be Assignable but not Default Constructable. Interestingly no mention is made of Copy Constructable in the value_type requirements. I assume this is inherited in the Allocator requirements. Hope this help, Michael -- ___________________________________ Michael Stevens Systems Engineering Navigation Systems, Estimation and Bayesian Filtering http://bayesclasses.sf.net ___________________________________

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boost::iostreams: only with std::cout?
by Dirk Griffioen 24 Mar '05

24 Mar '05

Hi, I would love to use the boost::iostreams lib, so I created a filter (which, in this case, does encryption) but instead of passing it std::cout I would like to pass it some other stream, a stringstream for instance (or any kind of ostream/istream, depending on the direction). However, I was very surprised to find the following code taking 100% cpu and not returning. It probably means I did something wrong, but I can't seem to find it. void test_encryption_filter() { const char* speech = "They sorely misunderestimate the American people if they " "think we will let them obtain nucular weapons. This " "malfeance will not stand."; // std::ostream which writes to standard output, filtered by a // encryption_output_filter. boost::io::filtering_ostream out; out.push(encryption::code_book::output_filter()); //out.push(std:cout); //this works std::ostringstream os; out.push(os); //this does not // Print unfiltered code. std::cout << "**** Speech unfiltered ****\n" << speech << "\n\n"; // Print filtered code: std::cout << "**** Speech with encryption filter ****\n"; out << speech << "\n\n"; } (testing puspose) filter looks like (namespace omitted): struct output_filter : public multichar_output_filter { template<typename Sink> void write(Sink& snk, const char* s, streamsize n) { while (n-- > 0) boost::io::put(snk, toupper(*s++)); } }; With std::cout this works fine, with std::ostringstream it does not. So could anyone please tell me what I am missing? Thanks in advance, Dirk ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you are not the intended recipient, any disclosure, copying, use, or distribution of the information included in this message and any attachments is prohibited. If you have received this email in error please notify our system management at postmaster(a)optiver.com and immediately and permanently delete this message and any attachments. ********************************************

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[build/regression testing] runtime failures
by Gennadiy Rozental 24 Mar '05

24 Mar '05

Is there any way to see a run command in case test fails at runtime? The same as we could see compiler command line if it fails at compile time Gennadiy

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[Boost-bugs] [ boost-Bugs-1170106 ] Investigate other kinds of heaps for dijkstra_shortest_paths
by SourceForge.net 24 Mar '05

24 Mar '05

Bugs item #1170106, was opened at 2005-03-24 14:35 Message generated for change (Tracker Item Submitted) made by Item Submitter You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=107586&aid=1170106&group_… Category: graph Group: None Status: Open Resolution: None Priority: 5 Submitted By: Douglas Gregor (dgregor) Assigned to: Douglas Gregor (dgregor) Summary: Investigate other kinds of heaps for dijkstra_shortest_paths Initial Comment: There are many types of heaps that provide good theoretical performance when used as a priority queue, e.g., by Dijkstra's shortest paths algorithm. The BGL contains implementations of two such data structures: a binary heap and a relaxed heap. The latter is used because it has been shown to provide the best overall performance. However, we should investigate other kinds of heaps, e.g., Fibonacci heaps, relaxed Fibonacci heaps, and run-relaxed heaps, to determine which option is best for the BGL. Dietmar Kuhl implemented several kinds of heaps in his Heaps library, which could be found in earlier versions of Boost. It was removed from Boost in the 1.27.0 timeframe because it had never been reviewed and was not maintained, but may still prove valuable for experiments. ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=107586&aid=1170106&group_… ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ Boost-bugs mailing list Boost-bugs(a)lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/boost-bugs

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[function] is function_equal used?
by Peter Dimov 24 Mar '05

24 Mar '05

The documentation says that comparisons require EqualityComparable, and contains_test never tests with objects that define function_equal instead of operator==. Also, there seems to be no test for boost::bind objects being put in a function<> (although there is one for lambda::bind). The reason I'm posting this is that I just switched boost::bind to implement function_equal instead of operator==, and this functionality isn't covered by our current tests. -- Peter Dimov http://www.pdimov.com

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[xpressive] doc bug?
by Thorsten Ottosen 24 Mar '05

24 Mar '05

The xpressive docs say sregex rex = sregex::compile( "(\\w+) (\\w+)!" ); can be expressed as sregex rex = (s1= +_w) >> ' ' >> (s2= +_w) >> '!'; . Shouldn't this be sregex rex = +_w >> ' ' >> +_w >> '!'; since you don't need to refer to previous matches? Thanks -Thorsten -- Thorsten Ottosen ---------------------------- www.dezide.com http://www.cs.aau.dk/index2.php?content=Research/mi www.boost.org www.open-std.org/JTC1/SC22/WG21/

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Naming Proposed Libraries
by David Abrahams 24 Mar '05

24 Mar '05

When discussing libraries in public that are under development but not yet accepted into Boost, I think it's problematic to refer to "The Boost <whatever> library" or "Boost.<whatever>" without qualification. Our peer-review process is respected, and these libraries are not yet officially blessed by Boost. I don't want to dilute the value of Boost acceptance. Can we please make a habit of prepending "The proposed" or something similar? For example, I suggest "The proposed Boost Interfaces library." Thanks! P.S. I hope it's obvious, but I don't think the documentation for the proposed library ought to resort to such contortions. -- Dave Abrahams Boost Consulting www.boost-consulting.com

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Does this algorithm exist?
by Michael Goldshteyn 24 Mar '05

24 Mar '05

Given: typedef std::deque<char> DequeString; std::string s("Hello sweet world!"); std::string word("sweet"); DequeString dequeString; // Copy "Hello sweet world!" into the deque string std::copy(s.begin(),s.end(),std::back_inserter(dequeString)); // Now, I want to find where "sweet" appears in the dequeString. An iterator to its location would be fine. // This doesn't quite do it, since it looks for _any_ occurrence of a character from word in dequeString std::find_first_of(dequeString.begin(),dequeString.end(),word.begin(),word.end()); // But, I want to find where _the whole_ word occurs in dequeString, similar to how std::string::find() does it: std::string::size_type wordPos=s.find(word); Is there something in boost or the standard C++ lib that can be used? Thanks, Michael Goldshteyn

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[type_traits] is_convertible regression on GCC 3.2 and 3.3
by Jonathan Turkanis 24 Mar '05

24 Mar '05

Hi, The following code causes a static assertion failure on GCC 3.2 (MinGW): #include <boost/static_assert.hpp> #include <boost/type_traits/is_convertible.hpp> struct base { }; struct middle : virtual base { }; struct derived : middle { }; BOOST_STATIC_ASSERT((boost::is_convertible<derived, middle>::value)); This problem is apparently responsible for the current failure of all the iostreams tests on the platforms gcc-3.2.3 and gcc-3.3.5. Jonathan

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