wxOrderedMap

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eranif
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Posts: 610
Joined: Tue Nov 29, 2005 7:10 pm
Location: Israel

wxOrderedMap

Post by eranif »

I often find myself in need of a container similar to std::map but that also maintains the order
in which elements were inserted.

Attached is my version of the wxOrderedMap

Code: Select all

#ifndef WX_ORDERED_MAP_H
#define WX_ORDERED_MAP_H

#include <map>
#include <list>

/// A container that allows fast insertions / retrieval of elements
/// And also maintains the order of which elements where inserted
template<typename Key, typename Value>
class wxOrderedMap
{
    typedef std::pair<Key, Value> Pair_t;
    typedef std::list<Pair_t> List_t;
    typedef std::map<Key, typename List_t::iterator> Map_t;

public:
    typedef typename List_t::const_iterator ConstIterator;
    typedef typename List_t::iterator Iterator;

protected:
    Map_t  m_map;
    List_t m_list;

public:
    wxOrderedMap() {}
    virtual ~wxOrderedMap() {
        m_map.clear();
        m_list.clear();
    }

    void Put(const Key& k, const Value& v) {
        Iterator iter = m_list.insert(m_list.end(), Pair_t(k, v));
        m_map.insert(std::make_pair<Key, Iterator>(k, iter));
    }

    Value &Get(const Key& k) {
        static Value NullValue;
        typename Map_t::iterator iter = m_map.find(k);
        if(iter == m_map.end())
            return NullValue;
        else {
            return iter->second->second;

        }
    }

    const Value &Get(const Key& k) const {
        static Value NullValue;
        typename Map_t::const_iterator iter = m_map.find(k);
        if(iter == m_map.end())
            return NullValue;
        else {
            return iter->second->second;

        }
    }

    bool Contains(const Key& k) const {
        return m_map.count(k);
    }

    void Remove(const Key &k) {
        typename Map_t::iterator iter = m_map.find(k);
        if(iter == m_map.end()) {
            // nothing to remove here
            return;
        }

        m_list.erase(iter->second);
        m_map.erase(iter);
    }

    ConstIterator Begin() const {
        return m_list.begin();
    }

    ConstIterator End() const {
        return m_list.end();
    }

    Iterator Begin() {
        return m_list.begin();
    }

    Iterator End() {
        return m_list.end();
    }
};

#endif // WX_ORDERED_MAP_H
Here is an example of usage:

Code: Select all

#include <stdio.h>
#include "wx_ordered_map.h"
#include <string>

void print(wxOrderedMap<std::string, std::string>& mp)
{
    // the iterator is of type:
    // std::pair<Key, Value>
    wxOrderedMap<std::string, std::string>::ConstIterator iter = mp.Begin();
    for(; iter != mp.End(); iter++) {
        printf("%s = %s\n", (*iter).first.c_str(),  (*iter).second.c_str());
    }
}

int main(int argc, char **argv)
{
	wxOrderedMap<std::string, std::string> mymap;
    
    mymap.Put("fruit",    "apple");
    mymap.Put("car",      "jeep");
    mymap.Put("game",     "wow");
    mymap.Put("computer", "linux");
    
    print(mymap);
    
    // Modify item (fetching an item is similar to fetching it from std::map)
    mymap.Get("fruit") = "banana";
    print(mymap);
    
    // Remove item (the complexity of removing an item is similar to std::map::find)
    mymap.Remove("car");
    print(mymap);
    
    if(!mymap.Contains("car")) {
        printf("Item 'car' does not exists\n");
    }
    
    return 0;
}


Eran
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OS: All
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