From cppreference.com
template<classH2,classP2>voidmerge(std::unordered_set<Key,H2,P2,Allocator>&source); (1) (since C++17)template<classH2,classP2>voidmerge(std::unordered_set<Key,H2,P2,Allocator>&&source); (2) (since C++17)template<classH2,classP2>voidmerge(std::unordered_multiset<Key,H2,P2,Allocator>&source); (3) (since C++17)template<classH2,classP2>voidmerge(std::unordered_multiset<Key,H2,P2,Allocator>&&source); (4) (since C++17)Attempts to extract ("splice") each element in source and insert it into *this using the hash function and key equality predicate of *this.
No elements are copied or moved, only the internal pointers of the container nodes are repointed. All pointers and references to the transferred elements remain valid, but now refer into *this, not into source. Iterators referring to the transferred elements and all iterators referring to *this are invalidated.
The behavior is undefined if get_allocator()!=source.get_allocator().
Parameters
source - compatible container to transfer the nodes from Return value
(none)
Complexity
Average case O(N), worst case O(N * size() + N), where N is source.size().
Example
Run this code
#include<iostream>#include<unordered_set>// print out a containertemplate<classOs,classK>Os&operator<<(Os&os,conststd::unordered_multiset<K>&v){os<<'['<<v.size()<<"] {";boolo{};for(constauto&e:v)os<<(o?", ":(o=1," "))<<e;returnos<<" }\n";}intmain(){std::unordered_multiset<char>p{'C','B','B','A'},q{'E','D','E','C'};std::cout<<"p: "<<p<<"q: "<<q;p.merge(q);std::cout<<"p.merge(q);\n"<<"p: "<<p<<"q: "<<q;}Possible output:
p: [4] { A, B, B, C } q: [4] { C, D, E, E } p.merge(q); p: [8] { E, E, D, A, B, B, C, C } q: [0] { } See also
(C++17)
extracts nodes from the container
(public member function)
inserts elements or nodes(since C++17)
(public member function)