From cppreference.com
template<classC2>voidmerge(std::map<Key,T,C2,Allocator>&source); (1) (since C++17)template<classC2>voidmerge(std::map<Key,T,C2,Allocator>&&source); (2) (since C++17)template<classC2>voidmerge(std::multimap<Key,T,C2,Allocator>&source); (3) (since C++17)template<classC2>voidmerge(std::multimap<Key,T,C2,Allocator>&&source); (4) (since C++17)Attempts to extract ("splice") each element in source and insert it into *this using the comparison object 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.
The behavior is undefined if get_allocator()!=source.get_allocator().
Parameters
source - compatible container to transfer the nodes from Return value
(none)
Exceptions
Does not throw unless comparison throws.
Complexity
N * log(size() + N)), where N is source.size().
Example
Run this code
#include<iostream>#include<map>#include<string>intmain(){std::multimap<int,std::string>ma{{1,"apple"},{5,"pear"},{10,"banana"}};std::multimap<int,std::string>mb{{2,"zorro"},{4,"batman"},{5,"X"},{8,"alpaca"}};std::multimap<int,std::string>u;u.merge(ma);std::cout<<"ma.size(): "<<ma.size()<<'\n';u.merge(mb);std::cout<<"mb.size(): "<<mb.size()<<'\n';for(autoconst&kv:u)std::cout<<kv.first<<", "<<kv.second<<'\n';}Output:
ma.size(): 0 mb.size(): 0 1, apple 2, zorro 4, batman 5, pear 5, X 8, alpaca 10, banana See also
(C++17)
extracts nodes from the container
(public member function)
inserts elements or nodes(since C++17)
(public member function)