In either case, no elements are copied or moved, only the internal pointers of the container nodes are repointed .

Extracting a node invalidates only the iterators to the extracted element, and preserves the relative order of the elements that are not erased. 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.

[edit]Parameters

[edit]Return value

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

[edit]Exceptions

[edit]Complexity

[edit]Notes

extract is the only way to change a key of a map element without reallocation:

std::map<int,std::string> m{{1,"mango"},{2,"papaya"},{3,"guava"}};auto nh= m.extract(2);nh.key()=4;m.insert(std::move(nh));// m == {{1, "mango"}, {3, "guava"}, {4, "papaya"}}

[edit]Example

#include <algorithm>#include <iostream>#include <string_view>#include <unordered_map> void print(std::string_view comment,constauto& data){std::cout<< comment;for(auto[k, v]: data)std::cout<<' '<< k<<'('<< v<<')'; std::cout<<'\n';} int main(){std::unordered_multimap<int,char> cont{{1,'a'},{2,'b'},{3,'c'}};     print("Start:", cont); // Extract node handle and change keyauto nh= cont.extract(1);    nh.key()=4;     print("After extract and before insert:", cont); // Insert node handle back    cont.insert(std::move(nh));     print("End:", cont);}

Start: 1(a) 2(b) 3(c)After extract and before insert: 2(b) 3(c)End: 2(b) 3(c) 4(a)

[edit]See also

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