Re: Copying from maps to lists or vectors

From:

mlimber <mlimber@gmail.com>

Newsgroups:

comp.lang.c++

Date:

17 Apr 2007 14:24:42 -0700

Message-ID:

<1176845082.477415.34820@d57g2000hsg.googlegroups.com>

On Apr 17, 2:55 pm, pallav <pallavgu...@gmail.com> wrote:

I have a map like this:

typedef boost::shared_ptr<Node> NodePtr;
typedef std::vector<NodePtr> NodeVecPtr;
typedef std::map<std::string, NodePtr> NodeMap;
typedef std::map<std:string, NodePtr>::iterator NodeMapItr;

NodeMap nmap;

In my classes, I often find myself copying the second arguments of
maps to lists/vectors like this.

NodeVecPtr nodes;
for (NodeMapItr itr = nmap.begin(); itr != nmap.end(); ++itr)
nodes.push_back(itr->second);

I may also have node be a list of NodePtrs as opposed to vectors. I'm
wondering if there is some standard STL routines, I can use to try to
reduce this kind of code being repeated. I now std::copy() exists but
it takes iterators. But since I'm dealing with maps, I'm not sure how
to pass the second value as an iterator. There is also
std::transform() but that also works with iterators.

I've been searching the web, and found stuff like boost::bind and
boost::iterator_adaptors that might work but I'm trying to read up the
documentation to figure out the syntax.

If somebody can help me in showing how I could accomplish this using
STL/boost features, this will be helpful. Thanks for you time.

I don't have time to work up a complete solution here, but here's a
snippet from Karlsson's Boost book (pp. 260f):

void print_string( const std::string& s ) {
   std::cout << s << '\n';
}

// ...

std::map<int, std::string> my_map;
my_map[0] = "Boost";
my_map[1] = "Bind";
std::for_each(
   my_map.begin(),
   my_map.end(),
   boost::bind( &print_string, boost::bind(
     &std::map<int,std::string>::value_type::second, _1)
   )
);

That should get you started.

Cheers! --M