Re: [Boost-users] newbie - graph library - vertex properties

Subject: Re: [Boost-users] newbie - graph library - vertex properties
From: Tobias Columbus (t.columbus_at_[hidden])
Date: 2009-12-17 03:13:49

Hi Suresh,

One advantage I can think of, is the following:
Suppose you're developing in a team and after some while you realize 
that your graph needs property XY. Then you don't have to mess around 
in some header file to adapt your team's graph classes, but you only 
have to adapt your code locally, initialize a property_map in your 
algorithm, use it and destroy it afterwards.

Another scenario would be that a graph is passed through some kind of 
pipeline and each pipeline step only needs to use local property_maps 
that saves memory, as the graph doesn't need to have internal all 
properties.

Finally I think the reason that property_maps are used in boost, is 
that they make generic programming much easier, as the library 
programmer doesn't fix the implementation of some property but the 
library user may choose the adequate property_map for his/her code.

Regards
Tobias

On Thursday 17 December 2009 06:54:17 am Suresh Kumar wrote:
> Hi Tobias
> 
> I managed to figure out how to use the property maps. When we can get
> vertex property as graph[vertex_descriptor] why property maps? again,
> when the above method is available, what do we gain by vertex_bundle
> property tag etc?
> 
> Thanks
> suresh
> 
> On Wed, Dec 16, 2009 at 5:00 PM, Suresh Kumar
> <suresh.amritapuri_at_[hidden]> wrote:
> > Hi,
> >
> > For example, I wrote the following:
> >  typedef property_map<Map, double Highway::*>::const_type IndexMap;
> >  IndexMap index = get(&Highway::miles,map);
> >
> > But I am unable to figure out how to get the actual vertex property
> > from the IndexMap index.
> >
> > Also, how do we use, get(vertex_bundle, map)?
> >
> > Thanks
> > suresh
> >
> >
> > On Wed, Dec 16, 2009 at 4:09 PM, Suresh Kumar
> > <suresh.amritapuri_at_[hidden]> wrote:
> >> Hi Tobias,
> >>
> >> Can you just show, how to access the vertex properties using the 
get()
> >>  function?. I know that map[vertex_descriptior] gives me the
> >> vertex_properties of that particular vertex. But I am unable to 
figure
> >> out how to use the get function for single vertex property as well 
as
> >> for the vertex_bundle,
> >>
> >> Thanks
> >> suresh
> >>
> >> On Tue, Dec 15, 2009 at 3:18 PM, Tobias Columbus 
<t.columbus_at_[hidden]> wrote:
> >>> Hi again,
> >>>
> >>> Try the following code, which just compiles fine with g++ 4.4.1 on 
my
> >>> system:
> >>>
> >>> struct City{...};
> >>> struct Highway{...};
> >>>
> >>> typedef ... Map;
> >>>
> >>> int main(){
> >>> Map map;
> >>> Map::vertex_descriptor v = add_vertex( map );
> >>> Map::vertex_descriptor u = add_vertex( map );
> >>> map[v].name = "Troy";
> >>> map[v].population = 49170;
> >>> map[v].zipcodes.push_back(12180);
> >>> Map::edge_descriptor e = add_edge( u, v, map ).first;
> >>> map[e].name = "I-87";
> >>> map[e].miles = 10;
> >>> map[e].speed_limit = 65;
> >>> map[e].lanes = 4;
> >>> map[e].divided = true;
> >>> return 0;
> >>> }
> >>>
> >>> Generally I would suggest reading
> >>> 
http://www.boost.org/doc/libs/1_41_0/libs/graph/doc/quick_tour.html
> >>> which gives a quick overview of how to handle graphs in BGL.
> >>>
> >>> If you work through this tutorial, vertex and edge properties 
will also
> >>> get explained.
> >>>
> >>> Regards
> >>> Tobias
> >>>
> >>> On Tuesday 15 December 2009 05:00:01 pm List User wrote:
> >>>> Hi Tobias Columbus,
> >>>>
> >>>> In fact I had tried that also. But then I got a funny message 
while
> >>> executing like this: Ubuntu 9.04, g++ 4.3.3
> >>>> //Map::vertex_descriptor v = *vertices(map).first;
> >>>>  Map::vertex_descriptor v = add_vertex(map);
> >>>>
> >>>> suresh_at_suresh-laptop:~/C++$ ./a.out
> >>>> *** glibc detected *** ./a.out: free(): invalid pointer: 
0x09f9c064
> >>> ***
> >>>> ======= Backtrace: =========
> >>>> /lib/tls/i686/cmov/libc.so.6[0xb7e6a604]
> >>>> /lib/tls/i686/cmov/libc.so.6(cfree+0x96)[0xb7e6c5b6]
> >>>> /usr/lib/libstdc++.so.6(_ZdlPv+0x21)[0xb804d231]
> >>>> ../a.out[0x8049e7d]
> >>>> ../a.out[0x8049ea7]
> >>>> ..
> >>>> ..
> >>>> ..
> >>>>
> >>>> so what to do next?
> >>>>
> >>>> suresh
> >>>>
> >>>>
> >>> _______________________________________________
> >>> Boost-users mailing list
> >>> Boost-users_at_[hidden]
> >>> http://lists.boost.org/mailman/listinfo.cgi/boost-users
> >>>
> >>
> >>
> >>
> >> --
> >> R. Suresh Kumar
> >> PhD Student, Vislab
> >> #216, Engineering II Bldg
> >> University of California, Riverside,
> >> CA 92521
> >>
> >
> >
> >
> > --
> > R. Suresh Kumar
> > PhD Student, Vislab
> > #216, Engineering II Bldg
> > University of California, Riverside,
> > CA 92521
> >
> 
> 
> 
> -- 
> R. Suresh Kumar
> PhD Student, Vislab
> #216, Engineering II Bldg
> University of California, Riverside,
> CA 92521
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
> 

-- 
__________________________
Tobias Columbus
t.columbus_at_[hidden]