std::multiset merge() method

since C++17

// (1) Non const version onlytemplate<class C2>void merge( std::set<Key, T, C2, Allocator>& source );// (2) Non const version onlytemplate<class C2>void merge( std::set<Key, T, C2, Allocator>&& source );// (3) Non const version onlytemplate<class C2>void merge( std::multiset<Key, T, C2, Allocator>& source );// (4) Non const version onlytemplate<class C2>void merge( std::multiset<Key, T, C2, Allocator>&& source );

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.

Undefined behaviour

The behavior is undefined if get_allocator() != source.get_allocator().

Parameters

• source - compatible container to transfer the nodes from

Return value

(none)

Complexity

O(N * log(size() + N)), where N is source.size().

Exceptions

Does not throw unless comparison throws.

Example

Main.cpp

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

Output

p: [4] { A, B, B, C }q: [4] { C, D, E, E }p.merge(q);p: [8] { A, B, B, C, C, D, E, E }q: [0] { }