How to implement a custom distributor to be used with std :: map?

Question

I am looking for a few pointers on how to implement a custom distributor to be used with std::map . I am interested in filling the map with millions of records without distribution for each element in the container (which is the default value for this container). The reason for this is the transfer of data to a third-party library that uses a map to store sample diagrams (QCustomPlot), and I feel that performance is hit when building large time series.

Is it possible to do this with one distribution, if the size of std::map is known in advance?

EDIT: Nodes will be loaded in ascending order into the container.

Answer 1

The only thing a custom allocator can do in this case is to avoid some of the overhead used by the default allocator caused by alignment, if you know the final size and the overhead of std :: map due to internal pointers, you can reserve a buffer with necessary size and in the user allocator to use all this continuous memory.

The amount of memory that will be saved will depend on the types that you use on your card, and I don’t think it will.

As mentioned in the comments of Öö Tiib and dau_sama, your best bet is boost :: flat_map, or you can just do it with

 std::vector<std::pair<Key,Value>> 

In any case, if you cannot change the third-party library, and it only accepts std :: map, you are still out of luck if it does not accept some type of iterator that you can adapt.