September 2002 - Boost-users

std::swap() vs boost::swap()
by Galante Michele 26 Sep '02

26 Sep '02

Boost classes that define a swap() member function usually also provide a global swap() function: namespace boost { class X { void swap(X &rhs); }; template<class T> void swap(X &lhs, X &rhs) { lhs.swap(rhs); } } Why is the global swap() function defined in namespace boost and not as a specialization of std::swap<>() in namespace std? Suppose I have a template function like the following: #include <algorithms> template <typename T> void do_something_and_swap(T &a, T &b) { // do something ... std::swap(a, b); } I want this template function to work with every type that is "swappable", but if I try to use it with boost::scoped_ptr<> the compiler fails because std::swap<>() is not specilized for boost::scoped_ptr<> and the generic definition of std::swap<>() requires the argument type to be copyable (and boost::scoped_ptr<> is noncopyable). I think I have read somewhere (but perhaps I'm wrong) that specialization of std::swap<>() for user defined types is allowed by the standard, so is there any other reason for not defining the global swap functions in namespace std? Michele Galante Zucchetti Centro Sistemi s.p.a. m.galante(a)centrosistemi.it

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RE: [Boost-Users] std::swap() vs boost::swap()
by scleary＠jerviswebb.com 26 Sep '02

26 Sep '02

> From: Galante Michele [mailto:M.Galante@centrosistemi.it] > > Suppose I have a template function like the following: > > #include <algorithms> > > template <typename T> > void do_something_and_swap(T &a, T &b) > { > // do something ... > std::swap(a, b); > } > > I want this template function to work with every type that is "swappable", > but if I try to use it with boost::scoped_ptr<> the compiler fails because > std::swap<>() is not specilized for boost::scoped_ptr<> and the generic > definition of std::swap<>() requires the argument type to be copyable (and > boost::scoped_ptr<> is noncopyable). The best way to provide this solution is to use an unqualified swap; Koenig lookup will ensure that the correct swap() is found for std:: and boost:: components. > I think I have read somewhere (but perhaps I'm wrong) that specialization of > std::swap<>() for user defined types is allowed by the standard, so is there > any other reason for not defining the global swap functions in namespace > std? Technically, specialization of std::swap is allowed. But overloading std::swap is not. These are often confused, but here's a concrete example: template <> void std::swap(boost::scoped_ptr<int> &, boost::scoped_ptr<int> &) is a specialization, and legal; but: template <typename T> void std::swap(boost::scoped_ptr<T> &, boost::scoped_ptr<T> &) is an overload, and not legal (currently). There's been a ton of discussion of this issue on the Boost.Developer's list; you can search the list archives if you're interested. -Steve

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Forte compiler template error
by Tanmay Patwardhan 26 Sep '02

26 Sep '02

Hi, I was trying to use the tokeniser lib and encountered this error: "/home/patwarta/boost_1_28_0/boost/iterator_adaptors.hpp", line 819: Error: The base "boost::detail::iterator_adaptor_traits_gen<boost::detail::token_ iterator_base<const char*>, std::basic_string<char, std::char_traits<char>, std::allocator<char>>, const std::basic_string<char, std::char_traits<char>, std::allocator<char>>&, const std::basic_string<char, std::char_traits<char>, std::allocator<char>>*, std::forward_iterator_tag, int>::type" must be a previously defined class or struct. "XMLbParserWrapper.cxx", line 11: Where: While specializing "boost::iterator_adaptor<boost::detail::token_iterator_ba se<const char*>, boost::detail::tokenizer_policy<std::basic_string<char, std::char_traits<char>, std::allocator<char>>, boost::char_delimiters_separator<char, std::char_traits<char>>>, std::basic_string<char, std::char_traits<char>, std::allocator<char>>, const std::basic_string<char, std::char_traits<char>, std::allocator<char>>&, const std::basic_string<char, std::char_traits<char>, std::allocator<char>>*, std::forward_iterator_tag, int> Any ideas? Thanks in advance, Tanmay

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RE: [Boost-Users] bind: I just keep trying...
by Mark Storer 25 Sep '02

25 Sep '02

I'm a little confused as to what you're aiming for here... a map of ints to function pointers (that can point to Y::foo)? This should do the trick, provided I'm recalling my function pointer declarations correctly std::map<int, short()(*X)> Further boost::bind creates an INSTANCE of a functor. Giving the compiler an instance when it wants a type is not a good way to keep it happy. Now if what you're actually after is calling Y::foo on a colleciton of Y's, then you don't need a collection of function pointers for each instance in the first place, which is where bind comes in. According to my flimsy understanding of bind (I haven't used it yet), this should do the trick: X someX; std::vector<Y> &wise = BuildYs(); // wise == plural of Y std::for_each( wise.begin(), wise.end(), boost::bind<short>(&Y::foo, &someX) ); If you want the X parameter to vary from one call of foo to the next, I suggest rolling your own loop... or incorporating the X* into Y, at which point you can get rid of the X* parameter, and use boost::bind(&Y::foo), or std::mem_fun(&Y::foo). --Mark Storer Software Engineer Cardiff Software #include <disclaimer> typedef std::disclaimer<Cardiff> Discard; -----Original Message----- From: dick.bridges(a)tais.com [mailto:dick.bridges@tais.com] Sent: Wednesday, September 25, 2002 4:08 PM To: boost-users(a)yahoogroups.com Subject: [Boost-Users] bind: I just keep trying... Everytime I think I have a clue, I'm reminded how little I REALLY understand. <error compiler='VC6SP4'> 'map' : invalid template argument for '_Ty', type expected </error> <snippet> struct X { } struct Y { short foo(X*); } struct Z { map<int, bind(&Y::foo, _1, _2) > myMap; } </snippet> I thought I saw how to do this somewhere on the website but I sure can't find it now. Any help GREATFULLY appreciated. 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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bind: I just keep trying...
by dick.bridges＠tais.com 25 Sep '02

25 Sep '02

Everytime I think I have a clue, I'm reminded how little I REALLY understand. <error compiler='VC6SP4'> 'map' : invalid template argument for '_Ty', type expected </error> <snippet> struct X { } struct Y { short foo(X*); } struct Z { map<int, bind(&Y::foo, _1, _2) > myMap; } </snippet> I thought I saw how to do this somewhere on the website but I sure can't find it now. Any help GREATFULLY appreciated.

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RE: [Boost-Users] pointer traints ?
by Mark Storer 25 Sep '02

25 Sep '02

Couldn't you do something along the lines of: template < typename PointerT, typeName RefereceT = &(*PointerT) > Only I think that's an address rather than a reference... How about: template < typename T > void f( T *ptr ) { T &ref = *ptr; // ... do something with ref ... } And what do you have against "->"? I don't think a reference's "." is any faster than a pointer's "->", so that shouldn't be a concern... just trying to save some knuckle grease? I don't get it. (I'm getting a lot of practice with that phrase since I started digging into STL & Boost) --Mark Storer Software Engineer Cardiff Software #include <disclaimer> typedef std::disclaimer<Cardiff> Discard; -----Original Message----- From: Bohdan [mailto:yg-boost-users@m.gmane.org] Sent: Monday, September 23, 2002 7:38 AM To: boost-users(a)yahoogroups.com Subject: [Boost-Users] pointer traints ? I have following code: template < typename PointerT > void f( PointerT ptr ) { ReferenceT ref = *ptr; // ... do something with ref ... } The problem is that ReferenceT is unknown inside f( ... ). If i had similar code for InteratorT instead of PointerT i was using iterator_traits. AFAIK there is no pointer traits for a raw and smart pointers and i can not use type_traits for smart pointers. So, the question is: "Is there some simple solution for this problem or this is just lack of pointer_traits in boost (std?) ?" regards, bohdan 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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BoostPython and VC 7.1 Everett ( again )
by Bernhard Glueck 25 Sep '02

25 Sep '02

Hi again. John, i checked out the RC_1_29_0 branch a few hours ago, and tried to compile everything. Using bjam everything builds fine, EXCEPT Boost Python... all other libs work as expected using MSVC1310.... Here is the error i get for all the targets of boost python: vc-C++ libs\python\build\bin\boost_python.dll\vc7\debug\runtime-link-dynamic\typ es.obj types.cpp E:\sdk\boost\boost\boost\python\reference.hpp(213) : error C2888: 'boost::shared _ptr' : symbol cannot be defined within namespace 'python' E:\sdk\boost\boost\boost\python\reference.hpp(222) : see reference to cl ass template instantiation 'boost::python::reference<T>' being compiled Maybe this just is not fixed yet... or its an error of mine Till next time Bernhard [Non-text portions of this message have been removed]

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Boost Python and VC7.1 ( Everett )
by Bernhard Glueck 25 Sep '02

25 Sep '02

Since we switched our projects to the new VC7.1 C++ Compiler ( MSVC 1310 ) recently i am not able to compile Boost Python anymore. The question is, if that's not supported at all, or if there is a workaround to do this. ( Compiling with VC7.0 works fine for me ) I upgraded to the most recent CVS version of Boost today, but still no luck ( using bjam "-sTOOLS=vc7" ) at least it does not spit out a "Unknown compiler version" warning anymore.... Any clues? Thanks, Bernhard Glueck [Non-text portions of this message have been removed]

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Quicker than boost RegEx?
by shevaxp 25 Sep '02

25 Sep '02

Hi. After trying boost RegEx++ in intensive string processing(NLP), performance is poor. Simply, for those who wants the quickest regex modules in C++/C , does anybody know what´s the best open source alternative? Thank you.

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How to visualise a graph
by tomislav_trajkovski 25 Sep '02

25 Sep '02

I am using the Boost 1.28.0 library on Windows 2000 with MSVC 6.0. Among other things I want to visualise a graph. The graph is a directed acyclic graph and what I want is an optimal presentation that occupies as little screen space as possible and where edges do not cross. Does anyone have any tips? Tomislav Trajkovski

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