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Boost lambda: iter_swap and treating lambda as iterator.
by chun ping wang 04 May '06

04 May '06

K the question is simple. How do i do iterator swap with lambda. lets say i have vector of U. vector<U> vecU; typedef vector<U>::iterator iter; iter beg(vecU.begin()); for_each(vec.begin(), vec.end(), ( if_(_1 == *beg) [ // swap the iterator between the current one and begin. ] ) );

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[boost] [test] Need help with BOOST_GLOBAL_FIXTURE usage
by Ed Johnson 04 May '06

04 May '06

Hi, I tried to use the BOOST_GLOBAL_FIXTURE macro using 1.33.1, but I can't seem to get it to run. The breakpoints do not stop on it, and there is no output from the constructor or destructor. http://lists.boost.org/Archives/boost/2005/12/98092.php ------ #define BOOST_AUTO_TEST_MAIN #include <iostream> struct MyConfig { MyConfig() { std::cout << "global setup\n"; } ~MyConfig() { std::cout << "global teardown\n"; } }; BOOST_GLOBAL_FIXTURE( MyConfig ) ; BOOST_GLOBAL_FIXTURE( MyConfig m ) { m; } Any ideas? Thanks, Ed

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Fusion 2. Vector Example
by John Christopher 03 May '06

03 May '06

Hello, At the bottom of the page http://spirit.sourceforge.net/dl_more/fusion_v2/libs/fusion/doc/html/fusion… there is the following example: vector<int, float> v(12, 5.5f); std::cout << at<0>(v) << std::endl; std::cout << at<1>(v) << std::endl; The example as such does not compile, Shouldn't it be:std::cout << at_c<0>(v) << std::endl;orstd::cout << at<boost::mpl::int_<0> >(v) << std::endl;

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Thread-safe smart pointers, hashtables without locking
by Ray Whitmer 03 May '06

03 May '06

I found the boost libraries and templates as I was looking for thread- safe smart pointers. I was unable to use shared_ptr because I needed to be able to reconstitute a smart pointer from a raw pointer at any time without losing the count, so the count needs to be internal to the object, not external, so I am using intrusive_ptr. Since I need my intrusive_ptr to be thread-safe, I included: #include "boost/detail/atomic_count.hpp" and then I declared my internal count to be of type: boost::detail::atomic_count which I then increment and decrement using the defined thread-safe operators from the add_ref and release methods, which should give me a relatively-thread-safe smart pointer with an internal count without having to do any actual locking. This already seems like I may be going beyond the official interface by explicitly relying on something in the boost detail directory. Is it wrong to rely on this? But what I need now goes a bit further. I need a hashtable for which lookups are thread-safe without doing any locking. I only want to lock for adding or removing to/from the table. I already have the hashtable implementation that does this that I have used in Java for quite a while. In Java, I assumed the writing of a 32-bit reference into the hashtable array (or a null) was fairly atomic (which seemed reasonable on a 32-bit machine with normal alignment, etc). I made sure in the implementation that a writer who locks and changes the hashtable never temporarily places the hashtable into a state where it cannot be correctly read by any non- locking reader. I am hoping this will continue to work in C++ with the intrusive_ptr array of a hashtable. intrusive_ptr seems to contain a single 32-bit value which is likely to be atomic, at least as long as I avoid 16- bit architectures. Is there any better way to guarantee this? With the exception of the reference count, the objects being kept by the hashtable are read-only, so this should allow me any number of threads simultaneously operating on the same massive shared data hashtables (which can get cleaned up when no longer in use, by looking at ref counts). I am just posting here to see if anyone knows of a missed trick or bad assumption I have made here using these or other boost mechaniisms. Is the thread-safe hashtable that does not require locking for reading something that many others would benefit from? It is quite a simple implementation. Thanks, Ray Whitmer

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[filesystem] boost::filesystem::filesystem_error thrown from boost::filesystem::is_directory is not caught by application
by Tim MacKinnon 03 May '06

03 May '06

OS - Solaris8 Compiler - gcc 3.4.0 boost version - 1_32 I have an application that is using the boost filesystem library. Here is a snippit of the code : void DirectoryInterface::listSubDirectories(String dirPath, FileList & dirList) { pthread_rwlock_rdlock(&DirectoryInterface::fsRwMutex); try { boost::filesystem::path filePath(dirPath, boost::filesystem::native); boost::filesystem::directory_iterator iter(filePath), iterEnd; if(boost::filesystem::exists(filePath)) { for (; iter != iterEnd; ++iter) { if(boost::filesystem::is_directory(*iter)) { .. do something } } } } catch (boost::filesystem::filesystem_error& ex) { .. do something } catch (std::exception& ex) { .. do something } catch (...) { .. do something } pthread_rwlock_unlock(&DirectoryInterface::fsRwMutex); } An exception is thrown by the call to boost::filesystem::is_directory() but is not caught by any of the catch blocks shown here. The application simply terminates with the following message : terminate called after throwing an instance of 'boost::filesystem::filesystem_error' what(): boost::filesystem::is_directory: "/opt/users/tmackinn/neDatabases/20060429050000.auto/10.1.26.25": No such file or directory Abort - core dumped Any ideas what I could be doing wrong? Thanks in advance, Tim

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[variant] determine if the type is a variant type
by Chris Weed 03 May '06

03 May '06

Hi, Is there a way to do something like is_variant<T>::value to determine if my type T is a variant type? Chris

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boost::multi_index_container different search key type
by bert hubert 03 May '06

03 May '06

Joaquin, list, In one of the last issues of the C/C++ User's Journal, Andrei Alexandrescu described the need for something better than std::map when using expensive keys: Let's start with two examples. The simplest one would involve the often-used map<string, something>: user names and user IDs, stock tickers and stock prices, class names and pointers to functions, words in Proust's opera and their counts...You can easily access the "something" if you have a key in the desired format. The problem is, you might have the key in a different format that forces a conversion. What if, for example, in your high-speed, high-availability, power-hungry, bonus-bringing stock market program, you have securities data come down the wire in raw char* format, but you need to look it up in a map<string, double>? More on http://www.ddj.com/dept/cpp/184402065 - might this be something boost::multi_index_container could be made to do? Not that boost::multi_index_container isn't wonderful enough already! Thanks. -- http://www.PowerDNS.com Open source, database driven DNS Software http://netherlabs.nl Open and Closed source services

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Is this possible with boost::multi_index?
by Jason House 03 May '06

03 May '06

Below is a small piece of code that I can't get to compile. gcc says: error: forward declaration of 'class search_node' Is there a way to get around this, or can I not embed a multi_index_container like that? I'm using boost 1_32_0 and gcc version 4.0.1 The code below is for a node within a search tree. Each node stores a > class search_node{ > int objective_value; // Objective function > position my_position; // Move location for this step in the search > std::list<position> positions_to_visit; // Future moves to consider in search > boost::multi_index_container < > search_node, > indexed_by< > ordered_unique <search_node, position, &search_node::my_position>, > ordered_non_unique<search_node, int, &search_node::objective_value> > > > search_results; > }; ... or am I just going down a wrong path? I'm trying to build a search tree. I know boost::graph exists, but don't know if it'd be more appropriate.

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Boost 1.33.1 build failure
by Paul Melis 03 May '06

03 May '06

I'm trying to build 1.33.1 on an AMD64 system, using bjam 3.1.12 and build command bjam "-sTOOLS=gcc" stage I get a horrible amount of error output which roughly reads Building Boost.Regex with the optional Unicode/ICU support disabled. Please refer to the Boost.Regex documentation for more information (and if you don't know what ICU is then you probably don't need it). Jamfile:278: in load-jamfiles *** argument error * rule stage ( name : sources + : requirements * : local-build * ) * called with: ( : /home1/rugrchpc/melis/boost_1_33_1/boost/compatibility/cpp_c_headers/cwchar /home1/rugrchpc/melis/boost_1_33_1/boost/compatibility/cpp_c_h eaders/csignal /home1/rugrchpc/melis/boost_1 [...] 1/rugrchpc/melis/boost_1_33_1/boost/pending/detail/int_iterator.hpp /home1/rugrchpc/melis/boost_1_33_1/boost/pending/detail/property.hpp /home1/rugrchpc/melis /boost_1_33_1/boost/pending/detail/disjoint_sets.hpp : <locate>stage <tree-subdirs>/home1/rugrchpc/melis/boost_1_33_1 <target>all : <suppress>true ) * missing argument name /home1/rugrchpc/melis/boost_1_33_1/tools/build/v1/boost-base.jam:2330:see definition of rule 'stage' being called /home1/rugrchpc/melis/boost_1_33_1/tools/build/v1/bootstrap.jam:21: in boost-build /home1/rugrchpc/melis/boost_1_33_1/boost-build.jam:16: in module scope I've tried looking at the Jamfile and line number mentioned, but I can't figure this stuff out. Any clue what is going on? Paul -- Paul Melis VR Specialist, Center for High-Performance Computing & Visualization, University of Groningen, The Netherlands T: +31 50 363 9298 E: p.e.c.melis(a)rug.nl W: http://www.rug.nl/rc/hpcv/index

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Re: [Boost-users] WG: defining a function<>-object with a returnvalue of the same type (recursive declaration)
by Oliver.Kowalke＠qimonda.com 03 May '06

03 May '06

Hmm - I would use boost::function instead of declaring a function-pointer object by myself. Regards, Oliver >On 5/2/06, Oliver.Kowalke(a)qimonda.com <Oliver.Kowalke(a)qimonda.com> wrote: >> how can I define a function<> object which returns a value of >> the same type: > >This was taken from GotW article 57: >http://www.gotw.ca/gotw//057.htm > > struct FuncPtr_; > typedef FuncPtr_ (*FuncPtr)(); > > struct FuncPtr_ > { > FuncPtr_( FuncPtr pp ) : p( pp ) { } > operator FuncPtr() { return p; } > FuncPtr p; > }; > >Now we can declare, define, and use f() naturally: > > FuncPtr_ f() { return f; } // natural return syntax > > int main() > { > FuncPtr p = f(); // natural usage syntax > p(); > } > >HTH, > >Michael Fawcett >_______________________________________________ >Boost-users mailing list >Boost-users(a)lists.boost.org >http://lists.boost.org/mailman/listinfo.cgi/boost-users

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