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 <map>
#include <iostream>
#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