Choosing a STL container with uniqueness and which keeps insertion ordering

Question

I am unable to decide which STL container to use in the following case:

1. I want to preserve the order of insertion of the elements
2. The elements in the

Answer 1

Boost MultiIndex should be able to do exactly what you want - you can just use one sequenced index to get the "ordered by insertion order" requirement, and either a hashed_unique or ordered_unique index to get the uniqueness requirement.

Answer 2

Implement a wrapper class over the container you choose (e.g. list, vector, deque), and rewrite the insertion/push_back methods to check that the inserted element is unique before inserting the element.

Unfortunately,I don't know any STL container to match your criteria.

Answer 3

No standard library container gives you what you want directly. I would start with a std::vector and write a free function to do the insert which does the find and the push_back for you. If this suffices, go no further. If you have performance problems, think about a more complicated solution.

Answer 4

You could do this:

• Create a wrapper around your element class with two members: your element, and an index. Let's call it 'InsertedElement'. The index will be the insertion order.

• Define comparison operator for this class, which only takes into account your element, but not the index. This will ensure the uniqueness of elements, while remembering their insertion order.

• Wrap a std::set and an insertion counter in another class. Then, when you want to insert a new element, either:

• It already exists, nothing to do.
• It does not: insert it in the map while giving it the current max index + 1.

Something like:

class CMagicContainer
{
  public:
    std::set<InsertedElement> collection;
    int indexGenerator;

    ...
};

Answer 5

There might be a good built in way to do this, but one rather simple way is to use both a hash_map and a list. Check the hash_map before each insertion, then insert into both. You'll want to encapsulate this in a class, probably.

Answer 6

If you already have boost installed, I like that option. Otherwise, why not just use a list or vector and add a check (find(k) == std::npos) on insertion? I suppose it could get kind of slow on a really, reallly large list, but for most cases it would work just fine.