looking for something like a std::map

Posted on 2001-09-11
Last Modified: 2013-12-14
I am looking for a stl class which is like a std::map, but which doesn't sort the elements, i.e. like a vector of pairs, but where you can do a find like you can with a std::map. Obviously I am aware that I could write a class that is a vector of pairs with a find method, however there is probably a stl class that does exactly what I want already.
Question by:duncanlatimer
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LVL 30

Expert Comment

ID: 6474342
You can try using a hash_map class.
hash_map is not part of the official C++ standards, but you can download a free copy of the class if you're intererested.

Expert Comment

ID: 6474362
I don't think there is such a thing.

Maybe multimap is what you want, it allows you to have multiple values with the same key.  It is sorted, however.

If sorting is a problem you could also try the hash associative container that is part of the SGI (and STLport) implementation of the STL.


for details and for the stlport download.

However, you should note that the entire point of these associative containers is to provide fast access by key value - so the classes need some way to store key values for efficient lookup.

Expert Comment

ID: 6474367
Didn't see your comment there Axter.
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Author Comment

ID: 6474420
As the order of the elemets in a hash_map are not guaranteed this will probably not work for me. I need to be able to retrieve the elements in the same order that I loaded them. And I also need to be able to do a find on a key.

Author Comment

ID: 6474444
I envisage that the container I am after has two different types of iterators, one type providing sorted access for finds etc, the other providing load sequence order access.

Expert Comment

ID: 6474448
The solution may well depend then on what your main concern is.  If speed of lookup is very important then you might consider storing maybe a vector and a map, maybe they could contain pointers to stored data structures, or maybe the vector could just contain key values.

i.e. something like:

vector<string> keyVector;
map<string,value>  mymap;

then you could implement a 'get by index' something like this:

value getByIndex(size_t index) const
    return mymap[keyVector[index]];

(you might want to change it add some error checking!).
LVL 30

Accepted Solution

Axter earned 100 total points
ID: 6474459
You can use a vector pair, and search for your data using the find_if function with a Predicate.

Example code:
#include <iostream>
#include <set>
#include <string>
#include <vector>
#include <algorithm>

class FindName {
     FindName(std::string Name) : m_Name(Name){}
     bool operator()(const std::pair<std::string,std::string> &Src)
          return (Src.first == m_Name);
     std::string m_Name;

int main(int argc, char* argv[])
     std::vector<std::pair<std::string,std::string> > myset;
     myset.push_back(std::pair<std::string,std::string>("Sue", "girl"));
     myset.push_back(std::pair<std::string,std::string>("Tom", "boy"));
     myset.push_back(std::pair<std::string,std::string>("Kim", "girl"));
     myset.push_back(std::pair<std::string,std::string>("Jack", "boy"));
     myset.push_back(std::pair<std::string,std::string>("Betty", "girl"));
     myset.push_back(std::pair<std::string,std::string>("Jill", "girl"));
     myset.push_back(std::pair<std::string,std::string>("Bob", "boy"));
     myset.push_back(std::pair<std::string,std::string>("David", "boy"));
     myset.push_back(std::pair<std::string,std::string>("Candy", "girl"));
     std::vector<std::pair<std::string,std::string> >::iterator  who =
     if (who != myset.end())
          std::string MaleOrFemale = who->second;
          std::cout << "David is a " << MaleOrFemale << std::endl;
     return 0;


Expert Comment

ID: 6474509
MFC has a CMap class

Author Comment

ID: 6474567
I am trying to avoid MFC and Axter's solution is exactly what I need so...

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