March 2006 - Boost-users - lists.boost.org

Re: [Boost-users] enable_shared_from_this - or an alternative..
by James Hughes 20 Mar '06

20 Mar '06

> -----Original Message----- > From: David Klein [mailto:d.klein@ascaron.com] > Sent: 20 March 2006 10:27 > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] enable_shared_from_this - or an > alternative.. > > > boost-users-bounces(a)lists.boost.org wrote: > > Hello All, > > > > I have a couple of classes that I want to self register themselves > > with a monitoring class. To do this they must pass a shared_ptr of > > themselves to the monitor register function. > > > > Therefore I need to make a shared_ptr form the this pointer, in the > > constructor. > > > > I have derived my classes from > enabled_shared_from_this...(code to get > > monitor omitted) > > > > //psuedo code.. > > monitor::AddSource1(boost::shared_ptr<CSource1>); > > monitor::AddSource2(boost::shared_ptr<CSource2>); > > > > class CSource1 : public enable_shared_from_this<CSource1> > > { > > CSource1() { Monitor->AddSource(shared_from_this()); }; > > } > > > > and > > > > class CSource2 : public base1, public > > enable_shared_from_this<CSource2> { > > CSource2() { Monitor->AddSource(shared_from_this()); };} > > } > > > > > > This all compile fine, but when run, the shared_from_this call > > asserts with a bad weak ptr - at the time of calling the > weak_ptr has > > no content, and looking at the boost code, I cannot see where it is > > supposed to get set to access the this value. > > > > Should I be using enable_shared_from_this in this way or is there a > > better way to convert the this ptr to a shared_ptr in a constructor > > that I need to use. > > > > > > James > > _______________________________________________ > > Boost-users mailing list > > Boost-users(a)lists.boost.org > > http://lists.boost.org/mailman/listinfo.cgi/boost-users > > hi james, > > see: http://boost.org/libs/smart_ptr/sp_techniques.html#in_constructor > > HTH dave > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/boost-users Thanks Dave, that does cover the problem well. However, I cannot use the null deleter mechanism suggested as the shared_ptr is passed on to monitor and is used there. The second scheme, using a factory fucntion, would seem to be approriate, however, how to I handle creation when the CSource1 class is actually to be used as a base class? If the factory function is in CSource1, it doesnt know about any derived classes. I don't want to have to write factory functions in every dervied class - that seems a waste. Is there a correct technique for getting around this issue? I am assuming a template of some description, but now sure what that entails. James >

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enable_shared_from_this - or an alternative..
by James Hughes 20 Mar '06

20 Mar '06

Hello All, I have a couple of classes that I want to self register themselves with a monitoring class. To do this they must pass a shared_ptr of themselves to the monitor register function. Therefore I need to make a shared_ptr form the this pointer, in the constructor. I have derived my classes from enabled_shared_from_this...(code to get monitor omitted) //psuedo code.. monitor::AddSource1(boost::shared_ptr<CSource1>); monitor::AddSource2(boost::shared_ptr<CSource2>); class CSource1 : public enable_shared_from_this<CSource1> { CSource1() { Monitor->AddSource(shared_from_this()); }; } and class CSource2 : public base1, public enable_shared_from_this<CSource2> { CSource2() { Monitor->AddSource(shared_from_this()); };} } This all compile fine, but when run, the shared_from_this call asserts with a bad weak ptr - at the time of calling the weak_ptr has no content, and looking at the boost code, I cannot see where it is supposed to get set to access the this value. Should I be using enable_shared_from_this in this way or is there a better way to convert the this ptr to a shared_ptr in a constructor that I need to use. James

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Re: [Boost-users] enable_shared_from_this - or an alternative..
by David Klein 20 Mar '06

20 Mar '06

boost-users-bounces(a)lists.boost.org wrote: > Hello All, > > I have a couple of classes that I want to self register themselves > with a monitoring class. To do this they must pass a shared_ptr of > themselves to the monitor register function. > > Therefore I need to make a shared_ptr form the this pointer, in the > constructor. > > I have derived my classes from enabled_shared_from_this...(code to get > monitor omitted) > > //psuedo code.. > monitor::AddSource1(boost::shared_ptr<CSource1>); > monitor::AddSource2(boost::shared_ptr<CSource2>); > > class CSource1 : public enable_shared_from_this<CSource1> > { > CSource1() { Monitor->AddSource(shared_from_this()); }; > } > > and > > class CSource2 : public base1, public > enable_shared_from_this<CSource2> { > CSource2() { Monitor->AddSource(shared_from_this()); };} > } > > > This all compile fine, but when run, the shared_from_this call > asserts with a bad weak ptr - at the time of calling the weak_ptr has > no content, and looking at the boost code, I cannot see where it is > supposed to get set to access the this value. > > Should I be using enable_shared_from_this in this way or is there a > better way to convert the this ptr to a shared_ptr in a constructor > that I need to use. > > > James > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/boost-users hi james, see: http://boost.org/libs/smart_ptr/sp_techniques.html#in_constructor HTH dave

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newbie question: how to make boost helloworld in linux
by kdsfinger＠gmail.com 20 Mar '06

20 Mar '06

hi, boost users Can someone tell me how to build boost helloworld.cpp in linux using g++? I have boost installed via yum in my fc3 box. Here is my code. //test.cpp #include <boost/shared_ptr.hpp> #include <iostream> int main(){ std::cout<<"helloworld"; return 0; } g++ test.cpp //can't find boost. Thanks in advance. zl2k

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MPL to get rid of cumbersome switch
by John Christopher 19 Mar '06

19 Mar '06

Hi; The program belows compiles and works but I'd like to simplify it, maybe using MPL. I spent some fascinating time educating myself on MPL, reading C++ Template Metaprogramming, but I am still at sea... to say the least. Basically the Functor contains a switch statement that is not convenient especially as the number of T classes will increase dramatically. Many thanks for any help on that JCR #include <iostream> #include <vector> #include <boost/mpl/vector.hpp> struct Tbase { Tbase() { std::cout << "Tbase" << std::endl; } }; struct T0 : public Tbase { T0() { std::cout << "T0" << std::endl; } }; struct T1 : public Tbase { T1() { std::cout << "T1" << std::endl; } }; typedef boost::mpl::vector<T0, T1> s; std::vector<Tbase*> vec; struct Functor { void operator()(const int& i) { switch(i) { case 0: vec.push_back(new T0); break; case 1: vec.push_back(new T1); break; } // I'd like to simplify the above swtich statement by writing something like: vec.push_back(new boost::mpl::at<s,i>::type); // but it does not compile and MinGW returns: // error: i cannot appear in a constant expression // error: template argument 2 is invalid. } }; int main (int argc, char ** argv) { std::vector<int> runtimeVec; runtimeVec.push_back(0); runtimeVec.push_back(1); runtimeVec.push_back(0); std::for_each(runtimeVec.begin(), runtimeVec.end(), Functor()); std::cout << vec.size() << std::endl; return 0; }

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Regex Bug in 1.33.1
by Olaf Bachmann 19 Mar '06

19 Mar '06

Hi, there seems to be a bug in version 1.33.1 of boost::regex: boost::regex_replace(std::string("foo"), boost::regex(".*"), "bar") returns "barbar" whereas 1.31.0 returns just "bar" (as I would expect). Any fix or hints out there? Thanks, Olaf

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Help with intrusive_ptr
by Thomas Laguzzi 17 Mar '06

17 Mar '06

Hello, I use intrusive_ptr with a class that holds the refcount and I derive from that class all my other classes. class TObject { public : int refcount ; TObject () { refcount = 0;} } I have defined the intrusive_..._addref and _release to increase and decrease/delete that refcount and everything works good! Anywhay sometimes I need to assign a derived object to another derived object of the same type instrusive_ptr <Derived> A = new Derived; . . . the problem: *A = *Derived(constr parameters). The point is that the refcount is assigned too (and becames 0) How are instrusive_addref and _release supposed to be implemented ? Any quick and clean solution for that ? I cannot write assignment operator for every derived class because... there are a lot of members :) Really thanks! Thomas

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Re: [Boost-users] [Variant]Pointers to using pointers
by Alan M. Carroll 17 Mar '06

17 Mar '06

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Unknown toolset: gcc-stlport
by Phlip 17 Mar '06

17 Mar '06

Boosties: We have a cross-platform solution using GNU g++ and VC7. Both sides use STLport. The documentation says to bond Boost (1.33.1) with STLport with this incantation: ./configure --with-toolset=gcc-stlport It emits: ### Unknown toolset: gcc-stlport ### ### Known toolsets are: acc, borland, cc, como, darwin, gcc, gcc-nocygwin, intel -linux, intel-win32, kcc, kylix, metrowerks, mingw, mipspro, msvc, qcc, sunpro, tru64cxx, vacpp, vc7, vmsdecc with no -stlport anywhere. When we try to wing it with just toolset=gcc, we get error messages. Googling for these reveals others got them too when they did not use the STLport toolset. I have heard that STLport now has an option to bond to Boost. Is that why Boost dropped an option to bond to STLport? If so, why did the same version of Boost like --with-toolset=vc-7_1-stlport? -- Phlip http://www.greencheese.org/ZeekLand <-- NOT a blog!!

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[Variant]Pointers to using pointers
by Conway Allen 17 Mar '06

17 Mar '06

The following, I suppose, produces a memory leak... is there any way to avoid this? Don't use variant with pointers... ? variant<T1*,T2*> vt; vt = new T1; vt = new T2; Thanks, Allen.

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