std::set<Key,Compare,Allocator>::merge
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Tables
std::set
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set::merge
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(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
Deduction guides (C++17)
template< class C2 >
void merge( std::set <Key, C2, Allocator>& source );
(1)
(since C++17) void merge( std::set <Key, C2, Allocator>& source );
(constexpr since C++26)
template< class C2 >
void merge( std::set <Key, C2, Allocator>&& source );
(2)
(since C++17) void merge( std::set <Key, C2, Allocator>&& source );
(constexpr since C++26)
template< class C2 >
void merge( std::multiset <Key, C2, Allocator>& source );
(3)
(since C++17) void merge( std::multiset <Key, C2, Allocator>& source );
(constexpr since C++26)
template< class C2 >
void merge( std::multiset <Key, C2, Allocator>&& source );
(4)
(since C++17) void merge( std::multiset <Key, C2, Allocator>&& source );
(constexpr since C++26)
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. If get_allocator() == source.get_allocator() is false, the behavior is undefined.
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.
[edit] Parameters
source
-
compatible container to transfer the nodes from
Exceptions
Does not throw unless comparison throws.
[edit] Complexity
Given \(\scriptsize S\)S as size() and \(\scriptsize N\)N as source.size():
1-4) \(\scriptsize S \cdot \log(S + N)\)S·log(S+N)
[edit] Example
Run this code
#include <iostream> #include <set> // print out a container template<class Os, class K> Os& operator<<(Os& os, const std::set <K>& v) { os << '[' << v.size() << "] {"; bool o{}; for (const auto& e : v) os << (o ? ", " : (o = 1, " ")) << e; return os << " }\n"; } int main() { std::set <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: [3] { A, B, C }
q: [3] { C, D, E }
p.merge(q);
p: [5] { A, B, C, D, E }
q: [1] { C }