std::multiset merge() method

od C++17

// (1) Non const version only
template<class C2>
void merge( std::set<Key, T, C2, Allocator>& source );

// (2) Non const version only
template<class C2>
void merge( std::set<Key, T, C2, Allocator>&& source );

// (3) Non const version only
template<class C2>
void merge( std::multiset<Key, T, C2, Allocator>& source );

// (4) Non const version only
template<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 container
template <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] { }