std::set<Key,Compare,Allocator>:: extract

In either case, no elements are copied or moved, only the internal pointers of the container nodes are repointed (rebalancing may occur, as with erase() ).

Extracting a node invalidates only the iterators to the extracted element. Pointers and references to the extracted element remain valid, but cannot be used while element is owned by a node handle: they become usable if the element is inserted into a container.

Parameters

Return value

A node handle that owns the extracted element, or empty node handle in case the element is not found in (2,3) .

Exceptions

Complexity

Notes

extract is the only way to take a move-only object out of a set:

std::set<move_only_type> s;
s.emplace(...);
move_only_type mot = std::move(s.extract(s.begin()).value());

Example

#include <algorithm>
#include <iostream>
#include <string_view>
#include <set>
 
void print(std::string_view comment, const auto& data)
{
    std::cout << comment;
    for (auto datum : data)
        std::cout << ' ' << datum;
 
    std::cout << '\n';
}
 
int main()
{
    std::set<int> cont{1, 2, 3};
 
    print("Start:", cont);
 
    // Extract node handle and change key
    auto nh = cont.extract(1);
    nh.value() = 4;
 
    print("After extract and before insert:", cont);
 
    // Insert node handle back
    cont.insert(std::move(nh));
 
    print("End:", cont);
}

Start: 1 2 3
After extract and before insert: 2 3
End: 2 3 4

See also