Re: Multimap: how to get a key list?

Brian <>
Mon, 1 Mar 2010 11:12:17 -0800 (PST)
On Feb 28, 5:09 pm, Sam <> wrote:

Rui Maciel writes:

Is there any way to get a list of keys from a multimap besides relying =

on a couple of nested

loops to assemble that list?

What nested loops? Only one loop is required to iterate over the multimap=


There is no single function that gives you a set of all keys stored in th=


multimap, but a single loop is all that's needed to retrieve all the keys=


It's fairly easy to define a template function that gives them to you,
something like this:

template<typename multimap_t>
void keys(const multimap_t &m,
          std::set<typename multimap_t::key_type> &k)
    for (typename multimap_t::const_iterator b(m.begin()), e(m.end())=


         b != e; ++b)


The std::set automatically takes care of deduping the multimap's keys.

I think that works fine. This might speed it up a little:

  template<typename multimap_t>
  void keys(const multimap_t &m,
            std::set<typename multimap_t::key_type> &k)
      typename std::set<typename multimap_t::key_type>::iterator
keys_end = k.end();
      for (typename multimap_t::const_iterator b(m.begin()),
           b != e; ++b)
           k.insert(keys_end, b->first);

That would work best if k is being passed in
as an empty container as seems likely.

Brian Wood
(651) 251-9384

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