NAME¶

std::map::merge - std::map::merge

Synopsis¶

template< class C2 > (1) (since C++17)
void merge( std::map<Key, T, C2, Allocator>& source );
template< class C2 > (2) (since C++17)
void merge( std::map<Key, T, C2, Allocator>&& source );
template< class C2 > (3) (since C++17)
void merge( std::multimap<Key, T, C2, Allocator>& source );
template< class C2 > (4) (since C++17)
void merge( std::multimap<Key, T, C2, Allocator>&& source );

Attempts to extract ("splice") each element in source and insert it into *this using
the comparison object of *this. If there is an element in *this with key equivalent
to the key of an element from source, then that element is not extracted from
source. 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.

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

Parameters¶

source - compatible container to transfer the nodes from

Return value¶

(none)

Exceptions¶

Does not throw unless comparison throws.

Complexity¶

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

Example¶

// Run this code

#include <iostream>
#include <map>
#include <string>

int main()
{
std::map<int, std::string> ma{{1, "apple"}, {5, "pear"}, {10, "banana"}};
std::map<int, std::string> mb{{2, "zorro"}, {4, "batman"}, {5, "X"}, {8, "alpaca"}};
std::map<int, std::string> u;
u.merge(ma);
std::cout << "ma.size(): " << ma.size() << '\n';
u.merge(mb);
std::cout << "mb.size(): " << mb.size() << '\n';
std::cout << "mb.at(5): " << mb.at(5) << '\n';
for (auto const& kv : u)
std::cout << kv.first << ", " << kv.second << '\n';
}

Output:¶

ma.size(): 0
mb.size(): 1
mb.at(5): X
1, apple
2, zorro
4, batman
5, pear
8, alpaca
10, banana

See also¶

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