Re: STL and finding objects by name

Alberto Ganesh Barbati <>
Fri, 4 Apr 2008 13:33:35 CST
Matthew Bucknall ha scritto:

class Thing

    Thing(const std::string& name):

    std::string get_name() const { return m_name; }

    bool operator< (const Thing& rhs) const
        return m_name < rhs.m_name;


    const std::string m_name;

std::set<Thing> things;

std::set<Thing>::iterator find_thing(const std::string& name)
    // this won't work of course, but this hopefully illustrates
    // what I want to do

    return things.find(name);

My question is, how can named objects (such as Thing) be stored in an
STL container such that they can then be efficiently found by name?
Note, I want named objects to have direct access to their name so
storing objects in a std::map<std::string, Thing> is no good IMHO
because items contained in the map don't have access to their keys.

Unfortunately, std::set is not very friendly in this scenario. The only
way to do proper lookup is to create an instance of Thing, for example
like this:

   std::set<Thing>::iterator find_thing(const std::string& name)
      return things.find(Thing(name));

If Thing is an heavy weight object, you could add a function set_name()
to change an object name, making it private to avoid involuntarily
breaking the std::set invariant, but making it a friend of find_thing so
that it can re-use one Thing instance:

   std::set<Thing>::iterator find_thing(const std::string& name)
      static Thing key;
      return things.find(key);

(not the most elegant code, I know.)

As a last resort, you could avoid using std::set entirely and rely on
smarter containers, for example Boost.MultiIndex



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