std::unordered_multiset<Key,Hash,KeyEqual,Allocator>::merge

template<class H2, class P2>
void merge( std::unordered_set<Key, H2, P2, Allocator>& source );

template<class H2, class P2>
void merge( std::unordered_set<Key, H2, P2, Allocator>&& source );

template<class H2, class P2>
void merge( std::unordered_multiset<Key, H2, P2, Allocator>& source );

template<class H2, class P2>
void merge( std::unordered_multiset<Key, H2, P2, Allocator>&& source );

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

Return value

(none).

Complexity

Average case O(N), worst case O(N*size()+N), where N is source.size().

Example

#include <iostream>
#include <unordered_set>
 
// print out a container
template <class Os, class K>
Os& operator<<(Os& os, const std::unordered_multiset<K>& v) {
    os << '[' << v.size() << "] {";
    bool o{};
    for (const auto& e : v)
        os << (o ? ", " : (o = 1, " ")) << e;
    return os << " }\n";
}
 
int main()
{
    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;
}

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