--- In Boost-Users@yahoogroups.com, "Jeff Garland" wrote:

I'm not sure what this would do on 1.29 b/c there have been lots of changes to lexical_cast. Of course I'm assuming this is an 'example' because with a blank string your program will core dump with an unhandled exception that occurs when it tries to construct a date from a blank string.

Yes, it was a stripped down example. Obviously replacing string constant with something meaningful will not affect compilation anyhow.

Dear Group, trying for several days, I simply don't get the correct usage of internal property maps and the connected_components algorithm. My graphs are very large (about 600 000 vertices), so that I am using internal instead of external property maps. Looking at one of Jeremy's postings (http://lists.boost.org/MailArchives/boost/msg15114.php) I defined my graph as follows: namespace boost { enum vertex_component_t {vertex_component = 113 }; BOOST_INSTALL_PROPERTY(vertex, component); } typedef typename boost::adjacency_list< boost::listS, //edges boost::listS, //nodes boost::undirectedS, //vertex properties boost::property > > // no edge properties > Graph; The code that uses internal property maps as an argument to compute_components comes below (actually, I am not sure whether this is a connected_components problem at all). typedef boost::property_map::type ComponentPropertyMap; ComponentPropertyMap component = boost::get(boost::vertex_component,g); int components_num = boost::connected_components(g,component); This looks quite straightforward and is in line with what Jeremy has posted. But I get the following compiler errors (using Boost 1.29 and gcc 3.2): [snip] /project/algorithmics/include/boost/property_map.hpp:344: no match for `const __gnu_cxx::__normal_iteratorboost::default_color_type > >& + const boost::detail::error_property_not_found&' operator What is going wrong? Do I have to use a color_type_t (Why? How?)? Any help is very welcome... Many thanks in advance Martin -- ----------------------------------------------------------------------------- Martin Okrslar MPI for Molecular Genetics phone: ++ 49 + 30 / 8413-1166 Computational Molecular Biology Fax: ++ 49 + 30 / 8413-1152 Ihnestrasse 73 email: okrslar@molgen.mpg.de D-14195 Berlin URL: http://cmb.molgen.mpg.de -----------------------------------------------------------------------------

...

The connected components algorithm uses a color map for internal storage. If you don't supply a color map, it tries to build a default color map using the vertex index property. That's where this is failing: when the vertex list type is listS, there is no default vertex_index property, so the code fails.

Is there any way I could have known that from the documentation? I mean,

Thanks a lot for your help! But (just in order to learn more about my beloved BGL): this is by no means an accusation, but I'd just like to be able to learn to work through the BGL without having to anoy the list with lots of question. I still think that I missed something. If this is so, please let me know. By the way: BGL saved me so much time... I can't even tell you... all the best Martin -- ----------------------------------------------------------------------------- Martin Okrslar MPI for Molecular Genetics phone: ++ 49 + 30 / 8413-1166 Computational Molecular Biology Fax: ++ 49 + 30 / 8413-1152 Ihnestrasse 73 email: okrslar@molgen.mpg.de D-14195 Berlin URL: http://cmb.molgen.mpg.de -----------------------------------------------------------------------------

Is the runtime behaviour correct? Have you been able to reproduce

--- In Boost-Users@yahoogroups.com, Kevlin Henney wrote: the

warning with a smaller example based just on lexical_cast?

I have not tried to run program yet because of much bigger problems with random library -- it simply fails to compile (see my original post). Reproducing warning with lexical cast is straightforward: #include #include <iostream> int main() { std::cout << boost::lexical_cast<int>("7") << std::endl; return 0; } reports the same warning I:\SW\EXTERNAL\BOOST_1_30_0\boost/lexical_cast.hpp(147) : warning C4800: 'void *' : forcing value to bool 'true' or 'false' (performance warning) I:\SW\EXTERNAL\BOOST_1_30_0\boost/lexical_cast.hpp(146) : while compiling class-template member function 'bool __thiscall boost::detail::lexical_stream::operator <<(char *const & )' Runtime behaviour of this program is correct. The warning is rather innocent, but annoying. Moreover the warning is abolutely correct -- returning stream from method with bool return type will convert void* to bool. Also it should be rather easy to fix, by explicitely casting it to bool.