NAME¶

std::unordered_multiset::merge - std::unordered_multiset::merge

Synopsis¶

template< class H2, class P2 > (1) (since C++17)
void merge( std::unordered_set<Key, H2, P2, Allocator>& source );
template< class H2, class P2 > (2) (since C++17)
void merge( std::unordered_set<Key, H2, P2, Allocator>&& source );
template< class H2, class P2 >
void merge( std::unordered_multiset<Key, H2, P2, Allocator>& (3) (since C++17)
source );
template< class H2, class P2 >
void merge( std::unordered_multiset<Key, H2, P2, Allocator>&& (4) (since C++17)
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¶

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 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;
}

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¶

extract extracts nodes from the container
(C++17) (public member function)
inserts elements
insert or nodes
(since C++17)
(public member function)