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Does std::map move around already inserted values when inserting new data ?
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insert() doesn't overwrite.
Yes -- when you insert an item into an std::map, you pass it by value, so what it contains is a copy of what you passed.
The map::emplace() is a built-in function in C++ STL which inserts the key and its element in the map container. It effectively increases the container size by one.
The map is implemented as a tree, and when you insert a new element, the tree may need to be rebalanced.
This does not invalidate any iterators or references to elements in the tree. This balancing is done via the manipulation of pointers, so you have nothing to worry about; the nodes themselves stay put.
Balancing involves changing the structure of the tree by telling nodes who their children, parents, and siblings are via re-assigning pointers, but this is an implementation detail. Logically nothing has changed.
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The standard does not mandate specific implementations of the STL, only the behavior and runtime characteristics. That said, a skip list or tree is a very likely implementation of std::map, so links will be updated, and the relative ordering will change, but the actual data is not going to be moving around.
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