template<class H2, class P2> void merge( std::unordered_map<Key, T, H2, P2, Allocator>& source ); | (1) | (since C++17) |
template<class H2, class P2> void merge( std::unordered_map<Key, T, H2, P2, Allocator>&& source ); | (2) | (since C++17) |
template<class H2, class P2> void merge( std::unordered_multimap<Key, T, H2, P2, Allocator>& source ); | (3) | (since C++17) |
template<class H2, class P2> void merge( std::unordered_multimap<Key, T, 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().
| source | - | compatible container to transfer the nodes from |
(none).
Average case O(N), worst case O(N*size()+N), where N is source.size().
#include <iostream>
#include <string>
#include <utility>
#include <unordered_map>
// print out a std::pair
template <class Os, class U, class V>
Os& operator<<(Os& os, const std::pair<U,V>& p) {
return os << '{' << p.first << ", " << p.second << '}';
}
// print out an associative container
template <class Os, class K, class V>
Os& operator<<(Os& os, const std::unordered_multimap<K, V>& v) {
os << '[' << v.size() << "] { ";
bool o{};
for (const auto& e : v)
os << (o ? ", " : (o = 1, "")) << e;
return os << " }\n";
}
int main()
{
std::unordered_multimap<std::string, int>
p{ {"C", 3}, {"B", 2}, {"A", 1}, {"A", 0} },
q{ {"E", 6}, {"E", 7}, {"D", 5}, {"A", 4} };
std::cout << "p: " << p << "q: " << q;
p.merge(q);
std::cout << "p.merge(q);\n" << "p: " << p << "q: " << q;
}Possible output:
p: [4] { {A, 1}, {A, 0}, {B, 2}, {C, 3} }
q: [4] { {A, 4}, {D, 5}, {E, 6}, {E, 7} }
p.merge(q);
p: [8] { {E, 6}, {E, 7}, {C, 3}, {A, 1}, {A, 0}, {A, 4}, {D, 5}, {B, 2} }
q: [0] { }|
(C++17) | extracts nodes from the container (public member function) |
|
(C++11) | inserts elements or nodes (since C++17) (public member function) |
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