May 2008 - Boost-users - lists.preview.boost.org

boost::variant implictly change a pointer type to bool
by Zhang, Yanbin 19 May '08

19 May '08

Can someone give me a hint about this. If I define a variant type boost::variant<double,std::string> var; and it will not compile if I do the following: int an_int(8); int* p_int(&an_int); var=p_int; std::cout << var.which() << std::endl; But if I define the type including bool: boost::variant<double,std::string,bool> var; the above code can compile and prints 2. It seems that when type bool is in the list, any pointer assigned to var will convert to a bool. The bad thing is that the compiler will not complain about it. Is there a way to prevent the assignment of a pointer type to a boost::variant variable? I am new to boost and I would be very appreciated if someone can help me on this. Yanbin Zhang

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shared_ptr<> null deleter
by Kevin Martin 19 May '08

19 May '08

I have just discovered to my delight that you can use shared_ptr with a null deleter to pass around stack based objects. This is great because a function shouldn't care whether a parameter passed to it is on the heap or stack. So I can write general functions to accept a shared_ptr and if I have to pass a stack based object I can just pass a null deleter. My question is whether the boost library has anywhere in it a null deleter object, or whether it is possible to define one in place with boost::lambda or similar? It seems silly that something that I imagine would be needed quite commonly is not included in the library. Thanks, Kevin Martin

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[test] in desperate need of examples
by Richard Dingwall 18 May '08

18 May '08

Can anyone point me in the direction of a Boost.Test example for the following scenario? 1. I have a standard install of boost trunk (svn co boost-trunk, make, make install) 2. For each class in my program, I have a cpp file containing tests for it 3. All the tests should be compiled together into a single executable I have read all the threads here I could find, and the (beta) documentation site, but I am finding all of the different link/main/initialization options very confusing, and I can't seem to find any complete examples. Help! Richard

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intrusive list with pointer_plus_bit
by Christian Holmquist 18 May '08

18 May '08

Hi, I have a class X : public intrusive::list_base_hook<> and would like to embed an additional member bool using the pointer_plus_bit. Can this be achieved using the value_traits somehow, and have the list working 'appropriately'? example code: #include <boost/function/function0.hpp> #include <boost/intrusive/list.hpp> #include <boost/intrusive/pointer_plus_bit.hpp> struct X : public boost::intrusive::list_base_hook<> { template<typename F> X(F const& f) : f_(f) {} boost::function0<void> f_; }; void foo() {} void test_intrusive() { typedef boost::intrusive::list<X> ilist; ilist list; list.push_back(*(new X(&foo))); X& x = list.back(); // How to set/get the bit on x? }; Thanks, Christian

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BoostCon & Bjam
by Tim St. Clair 18 May '08

18 May '08

Folks - I've heard various mumblings from sources regarding the future of BJAM, and I would honestly like to know what the verdict is. I've also heard a lot of smack about it, which I consider to be more dogma then anything. Also, I must say, as a cross platform developer I have yet to find it's equal, and would perfer to illuminate dogma where it may exist, vs. throwing up our arms hold heartedly. If that means developing a users guide to help "boost" them into bjam, then I would be happy to contribute. Cheers, Tim

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Xcode 3 and boost-1_35
by Tom Lenaerts 18 May '08

18 May '08

Hi everyone, I recently obtained a new Mackbook pro with Os X leopard on it. I installed the latest Boost library using Macports . Yet when I take my previous projects (build on Os X tiger with Xcode 2.5 and Boost -1_34_1) I have problems with the programming_options library. So I created a simple command line project (see main in the end of this mail) to track down the problem and found that Xcode is having problems with strings in the program options. I'm writing Xcode because when I compile the same code from command line using g++ there are no problems at all. So it has to be somewhere in the specifications. I'm pretty sure that I specified where to look for the header files and the libraries. I added the libprogram_options_mt-1_35.dylib as a framework to the Xcode project. The code compiles in Release configuration but when I try to run it I get : >>> ./test -R 1 -L 1 -A 20 -S data.in -O result.txt terminate called after throwing an instance of 'boost::bad_any_cast' what(): boost::bad_any_cast: failed conversion using boost::any_cast Abort trap The problem arises as soon as the code starts to process the vector<string> arguments. When I then try to compile the samen code in Debug model I get three errors: mkdir /Users/tlenaert/Desktop/test/build/Debug cd /Users/tlenaert/Desktop/test /Developer/usr/bin/g++-4.0 -o /Users/tlenaert/Desktop/test/build/Debug/test -L/Users/tlenaert/Desktop/test/build/Debug -L/opt/local/lib -L/opt/local/lib -F/Users/tlenaert/Desktop/test/build/Debug -filelist /Users/tlenaert/Desktop/test/build/test.build/Debug/test.build/Objects-normal/i386/test.LinkFileList -lboost_program_options-mt-1_35 -arch i386 -mmacosx-version-min=10.5 -isysroot /Developer/SDKs/MacOSX10.5.sdk Undefined symbols: "boost::program_options::value_semantic_codecvt_helper<char>::parse(boost::any&, __gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&, bool) const", referenced from: vtable for boost::program_options::typed_value<__gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, char>in main.o vtable for boost::program_options::typed_value<int, char>in main.o vtable for boost::program_options::typed_value<double, char>in main.o "boost::program_options::detail::cmdline::cmdline(__gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&)", referenced from: boost::program_options::basic_command_line_parser<char>::basic_command_line_parser(int, char**)in main.o "boost::program_options::validate(boost::any&, __gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >*, int)", referenced from: void boost::program_options::validate<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, char>(boost::any&, __gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&, __gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >*, int)in main.o ld: symbol(s) not found collect2: ld returned 1 exit status "boost::program_options::value_semantic_codecvt_helper<char>::parse(boost::any&, __gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&, bool) const", referenced from: vtable for boost::program_options::typed_value<__gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, char>in main.o vtable for boost::program_options::typed_value<int, char>in main.o vtable for boost::program_options::typed_value<double, char>in main.o "boost::program_options::detail::cmdline::cmdline(__gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&)", referenced from: boost::program_options::basic_command_line_parser<char>::basic_command_line_parser(int, char**)in main.o "boost::program_options::validate(boost::any&, __gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >*, int)", referenced from: void boost::program_options::validate<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, char>(boost::any&, __gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&, __gnu_debug_def::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >*, int)in main.o ld: symbol(s) not found collect2: ld returned 1 exit status Build failed (3 errors) IS there anyone here who cam across a similar problem or who can help me out? Thanks a lot Tom ==================== main.cpp =================== #include <iostream> #include <vector> #include <string> #include <boost/program_options.hpp> namespace po = boost::program_options; using namespace std; int main (int argc, char * argv[]) { //setting up the simulation double run; double additional; int limit; po::options_description desc("Allowed options"); desc.add_options() ("help", "produce help message") ("run,R", po::value<double>(&run)->default_value(1000), "identification of run") ("limit,L", po::value<int>(&limit)->default_value(1), "threshold for stochastic and deterministic dynamics") ("additional,A", po::value<double>(&additional)->default_value(20), "Additional years to run after threshold is reached") ("settings,S",po::value<vector<string> >(),"File with simulation settings") ("output,O",po::value<vector<string> >(),"Output file"); po::variables_map vm; po::store(po::parse_command_line(argc, argv, desc), vm); po::notify(vm); if (vm.count("help")) { cout << desc << "n"; return 1; } string inputfname; if(vm.count("settings")){ inputfname = (vm["settings"].as<vector<string> >())[0]; cout << "Input file is "<< inputfname << endl; } string ouputfname; if(vm.count("output")){ ouputfname = (vm["output"].as<vector<string> >())[0]; cout << "Output file is "<< ouputfname << endl; } return 0; }

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[shared_from_this] why doesn't _internal_weak_this need to be initialized?
by Jose Martinez 18 May '08

18 May '08

>It gets initialized by the shared_ptr constructor. Frank, when I call user_count() on the _internal_weak_ptr before calling share_from_this() I get back 1. So are you referring to the first shared_ptr constructor in main() (vs the constructor in share_from_this())? If so how is it initialized? The shared_ptr constructor gets passed a reference to the object being pointed, are you saying it goes and searches out for _internal_weak_ptr within that object and initializes it if it finds it? thanks jose "survival first, then happiness as we can manage it"

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[shared_from_this] why doesn't _internal_weak_this need to be initialized?
by Jose Martinez 18 May '08

18 May '08

In the shared_from_this() function of the enable_shared_from_this base class, the weak pointer _internal_weak_this is never initialized. Why is that so? The use_count of the _internal_weak_ptr is at least 1 as long as there is a shared_ptr already pointing to *this. How does the un-initialized weak_ptr know that there is a shared_ptr already created and how can it access the number of references? I'm sure there is a simple explanation that I am not catching in my readings. thanks jose "survival first, then happiness as we can manage it"

2 1

STL containers and incomplete types
by Maik Beckmann 17 May '08

17 May '08

Hello, Does boost got something to do this struct node { std::vector<node> children; // node is incomplete }; in a way which conform with the standard which disallows STL containers of incomplete types? thx, -- Maik

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[bgl] Finding the minimum cut
by Chris Jefferson 17 May '08

17 May '08

I'm looking to find the global 'vertex cut' of an undirected graph. While there are special algorithms for doing this, but I have found it can be mapped into a set of directed min-cut problems, which can be mapped into the bgl. However, it seems that while I can find the value of the max flow, I cannot find the corresponding minimum cut. Am I missing something very obvious? Chris

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