- Boost-users - lists.boost.org

Re: operator<< for boost::any
by Patrick Guio 10 Dec '01

10 Dec '01

On Sun, 9 Dec 2001, assaflavieatwork wrote: > If all you want to do is output the value inside the 'any' you can > add a virtual member to the place_holder/holder classes (inside any's > impl) that will output to a ostream&. That is exactly my need > in place_holder: > virtual ostream& write(ostream&) = 0; You mean placeholder? I have added this declaration as a pure virtual function in the queries part. class placeholder { ... public: // queries ... virtual ostream& write(ostream&) = 0; }; > in holder: > ostream& write(ostream& o) { o << held; }; > I have added the declaration in the derived class holder from the abstract base class placeholder template<typename ValueType> class holder : public placeholder { ... public: // queries ... ostream& write(std::ostream& os) { os << held; } public: // representation ValueType held; }; > outside any: > std::ostream& operator << (std::ostream& out, const any& value) { > return value.write(out); > }; I don't understand how this can work since the class any contains a pointer to an object of class placeholder. This object has a member function write but not the class any itself? I have another comment more general about the any class The declaration placeholder * content; in the any class might be public or private depending on the value of the value of the define BOOST_NO_MEMBER_TEMPLATE_FRIENDS. Is it safe? #ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS private: // representation template<typename ValueType> friend ValueType * any_cast(any *); #else public: // representation (public so any_cast can be non-friend) #endif placeholder * content; }; > > But that of course means changing the any.hpp file which of course > isn't something everyone is willing to do... Why not including a simple overloading of the << operator? > > Anyway, it won't help you if you want to read the any back from an > istream. You'll have to write some type information to the stream or > else you'll just interpret everything as a string. > I understand that but that is not what I want to do. Sincerely Patrick Guio

2 1

RE: [Boost-Users] Re: shared_ptr and inheritance
by Björn Karlsson 10 Dec '01

10 Dec '01

> From: rz0 [mailto:rz0@yahoo.com] > > > > > >VC++ 6.0 flags the above lines with a conversion error. > > > > > >Is there any way to resolve this? > > > > Can you just define b and c as boost::shared_ptr<A>? > > Hi Jon > > Thank you very much for the response. Unfortunately this will cause > the same problem that I ran into with std::auto_ptr and that is > methods funcB and funcC which are exclusive to B and C are not > allowed to be called. > > Take care > RZ > It seems to me that the problem is in the design - you're trying to use inheritance for the convenience of placeholding (and maybe insulation). That won't work (as you've seen). Even with a compiler that allows the code to compile (those that support member templates will) you will not get the behaviour that you want - funcB and funcC can never be called (from client code). The reason that the code compiles cleanly is that the conversion from B* or C* to A* is valid - but there's no way you can dynamically change the static type of "boost::shared_ptr<A> aptr;". If you really need to get this to work, it is still possible: You could use boost::any, and any_cast through all the possible types. This, however, is not very flexible, and IMO not very readable or maintainable. Regards, Bjorn Karlsson [Non-text portions of this message have been removed]

2 1

shared_ptr and inheritance
by rz0 10 Dec '01

10 Dec '01

Hello I have the following scenario: #include <iostream> #include <boost/smart_ptr.hpp> class A { public: virtual void func1() { std::cout << "A::func1" << std::endl; } }; class B : public A { public: void func1() { std::cout << "B::func1" << std::endl; } void funcB() { std::cout << "B::funcB" << std::endl; } }; class C : public A { public: void func1() { std::cout << "C::func1" << std::endl; } void funcC() { std::cout << "C::funcB" << std::endl; } }; class Holder { boost::shared_ptr<A> aptr; public: void setclass(boost::shared_ptr<A> a) { aptr = a; } void callfunc() { aptr->func1(); } }; int main() { Holder holder; boost::shared_ptr<B> b(new B()); boost::shared_ptr<C> c(new C()); holder.setclass(b); //<------- holder.setclass(c); //<------- holder.callfunc(); return 0; } VC++ 6.0 flags the above lines with a conversion error. Is there any way to resolve this? Thanks very much in advance.

2 3

Can't build Python-lib with VC
by swbuddy2001 08 Dec '01

08 Dec '01

Hi all, i'm trying to build the Boost-Python library (Version 1.26.0) with VS6 using SP6 and i get the following ErrorMsg. Compiling... types.cpp ..\..\..\boost/bind/mem_fn_template.hpp(135) : error C2562: '()' : 'void' function returning a value ..\..\..\boost/bind/mem_fn_template.hpp(133) : see declaration of '()' ..\..\..\boost/bind.hpp(735) : see reference to function template instantiation 'void __thiscall boost::_mfi::cmf1<void,class boost::python::detail::type_object_base,struct _object *>::operator () (class boost::python::detail::type_object_base *const & ,struct _object *) const' being compiled Any suggestions what i can do to get types.cpp compiled? Thanks in advance, Jürgen

2 4

explanation about cyclic_ptr in smart_ptr
by ma_ting_chong 06 Dec '01

06 Dec '01

How do cyclic_ptr work in the smarttest.zip in smart_ptr library?

1 0

Need Digest
by Daryle Walker 05 Dec '01

05 Dec '01

I guess Yahoo Groups had a data burp on 21 Nov 2001, because I didn't get digest 22. Could anyone send it to me? -- Daryle Walker Mac, Internet, and Video Game Junkie darylew AT mac DOT com

1 0

OT: Is there a forum for Loki anywhere on the 'net?
by Gooch, Allen 04 Dec '01

04 Dec '01

I know that pieces of Loki are being reviewed for inclusion into Boost, but I was wondering if there is any sort of forum for questions regarding the use of Loki itself, specifically Loki::SmartPtr. Please respond by email to avoid list clutter, unless it relates to boost use. TIA, Allen Gooch

2 1

Re: [Boost-Users] Re: Installing on Windows 95 with Mingw32 1.1
by John Maddock 02 Dec '01

02 Dec '01

>ISTR that when I tried to use boost.threads in the past on Win98, I >encountered problems with the TSS code as well - with MSVC. I didn't see the >page faults since a catch(...) handler on MSVC eats them but the results >were worse than that - the machine locked up in about half of the cases, in >the other half the thread that faulted died without warning. I haven't seen that. >I think that it's possible that the problem is not gcc-specific. Note that >both your successes use pthreads-win32, not the native win32 implementation >of Boost.Threads. the tests run fine using the win32 threads API as well (at least for me), the reason I used pthreads-win32 was to make the tests more directly comparable to cygwin (which has it's own pthreads API). - John Maddock http://ourworld.compuserve.com/homepages/john_maddock/

1 0

graph library compilation on VC++
by zhang3284＠yahoo.com 02 Dec '01

02 Dec '01

I'm new to BGL and studying the examples provided with the library. Here is a problem I'm having: I compiled a program, for example,dfs- example.cpp, it was fine. And then I changed the program a little bit, and tried to recompile it, I got the following error: boost\iterator_adaptors.hpp(845) : fatal error C1001: INTERNAL COMPILER ERROR Then I tried Rebuild All or cleaned the project first, and then compiled it. It became OK again. I'm using VC++ 6.0 SP5. Any comment would be appreciated. Thanks. Yingjun Zhang

2 1

operator<< for boost::any
by Patrick Guio 01 Dec '01

01 Dec '01

Dear all, I am trying to use the any class in a project. I would need to print elements of a vector<any>. I have come to the following solution as an example: template<class T> inline ostream& operator<<(ostream &os, const vector<T> &v) { vector<T>::const_iterator iter(v.begin()); for (int c(0), n(v.size()); c<n-1; c++) os << *iter++ << ','; return os << *iter; } typedef vector<bool> vectb; int main() { vector<any> values; double f(2.0); string s("hello"); int i(100); bool b(false); vectb vectbool; vectbool.push_back(true); vectbool.push_back(false); vectbool.push_back(true); vectbool.push_back(true); vectbool.push_back(false); vectbool.push_back(true); values.push_back(f); values.push_back(s); values.push_back(i); values.push_back(b); values.push_back(vectbool); for (vector<any>::iterator i(values.begin()), last(values.end()); i!=last; i++) { if (any_cast<bool>(i)) cout << *any_cast<bool>(i) << endl; else if (any_cast<int>(i)) cout << *any_cast<int>(i) << endl; else if (any_cast<float>(i)) cout << *any_cast<float>(i) << endl; else if (any_cast<double>(i)) cout << *any_cast<double>(i) << endl; else if (any_cast<string>(i)) cout << *any_cast<string>(i) << endl; else if (any_cast<vectb>(i)) cout << *any_cast<vectb>(i) << endl; } } But I would like a more general solution without to make assumptions about the type. Do you have any ideas? Another point is that I cannot figure out how to convert the solution below in terms of a friend ostream& operator<<(ostream &os, const any &rhs) I cannot get this compiled with g++ v 2.95 friend ostream& operator<<(ostream &os, const any &rhs) { return os << *any_cast<bool>(rhs); } Sincerely, Patrick ====================================================================== Patrick Guio Institute of Physics, University of Oslo P.O. box 1048, Blindern, N-0316 Oslo Tel : (+47) 22 84 40 60 - Fax : (+47) 22 85 56 71 E-mail : patrick.guio(a)fys.uio.no URL : http://folk.uio.no/~patricg

4 4