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std::multimap::multimap(3) C++ Standard Libary std::multimap::multimap(3) NAME std::multimap::multimap - std::multimap::multimap Synopsis multimap(); (until C++11) multimap() (since C++11) : multimap(Compare()) {} explicit multimap( const Compare& comp, (2) const Allocator& alloc = Allocator() ); explicit multimap( const Allocator& alloc ); (3) (since C++11) template< class InputIt > multimap( InputIt first, InputIt last, (4) const Compare& comp = Compare(), const Allocator& alloc = Allocator() ); template< class InputIt > multimap( InputIt first, InputIt last, (5) (since C++14) const Allocator& alloc ) : multimap(first, last, Compare(), alloc) {} multimap( const multimap& other ); (6) multimap( const multimap& other, const Allocator& alloc ); (7) (since C++11) multimap( multimap&& other ); (8) (since C++11) multimap( multimap&& other, const Allocator& alloc ); (9) (since C++11) multimap( std::initializer_list<value_type> init, (1) const Compare& comp = Compare(), (10) (since C++11) const Allocator& alloc = Allocator() ); multimap( std::initializer_list<value_type> init, const Allocator& alloc ) (11) (since C++14) : multimap(init, Compare(), alloc) {} template< container-compatible-range<value_type> R > multimap( std::from_range_t, R&& rg, (12) (since C++23) const Compare& comp = Compare(), const Allocator& alloc = Allocator() ); template< container-compatible-range<value_type> R > multimap( std::from_range_t, R&& rg, const Allocator& alloc ) (13) (since C++23) : multimap(std::from_range, std::forward<R>(rg), Compare(), alloc) {} Constructs new container from a variety of data sources and option- ally using user supplied allocator alloc or comparison function object comp. 1-3) Constructs an empty container. 4,5) Constructs the container with the contents of the range [first, last). If [first, last) is not a valid range, the behavior is undefined. 6,7) Copy constructor. Constructs the container with the copy of the contents of other. If alloc is not provided, allocator is obtained by calling (since std::allocator_traits<allocator_type>:: C++11) select_on_container_copy_construction(other.get_allocator()). During class template argument deduction, only the first argument contributes (since to the deduction of the container's Allocator template parameter. C++23) 8,9) Move constructor. Constructs the container with the contents of other using move semantics. If alloc is not provided, allocator is obtained by move-construction from the allocator belonging to other. During class template argument deduction, only the first argument contributes to the deduction of the container's Allocator template (since C++23) parameter. 10,11) Initializer-list constructor. Constructs the container with the contents of the initializer list init. 12,13) Constructs the container with the contents of rg. Parameters alloc - allocator to use for all memory allocations of this container comp - comparison function object to use for all comparisons of keys first, last - the range to copy the elements from other - another container to be used as source to initialize the elements of the container with init - initializer list to initialize the elements of the container with rg - a container compatible range, that is, an input_range whose elements are convertible to value_type Type requirements - InputIt must meet the requirements of LegacyInputIterator. - Compare must meet the requirements of Compare. - Allocator must meet the requirements of Allocator. Complexity 1-3) Constant. 4,5) \(\scriptsize N \cdot log(N)\)Nlog(N) where \(\scriptsize N\)N is std::distance(first, last) in general, linear in \(\scriptsize N\)N if [first, last) is already sorted by value_comp(). 6,7) Linear in size of other. 8,9) Constant. If alloc is given and alloc != other.get_allocator(), then linear. 10,11) \(\scriptsize N \cdot log(N)\)Nlog(N) where \(\scriptsize N\)N is init.size() in general, linear in \(\scriptsize N\)N if init is al- ready sorted by value_comp(). 12,13) \(\scriptsize N \cdot log(N)\)Nlog(N) where \(\scriptsize N\)N is ranges::distance(rg) in general, linear in \(\scriptsize N\)N if rg is already sorted by value_comp(). Exceptions Calls to Allocator::allocate may throw. Notes After container move construction (overload (8,9)), references, pointers, and iterators (other than the end iterator) to other remain valid, but refer to elements that are now in *this. The current standard makes this guarantee via the blanket statement in [container.reqmts]/67, and a more direct guarantee is under consideration via LWG issue 2321. Although not formally required until C++23, some implementations has already put the template parameter Allocator into non-deduced contexts in earlier modes. Feature-test macro Value Std Feature __cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construc- tion and insertion; overloads (12,13) Example // Run this code #include <iostream> #include <map> #include <utility> struct Point { double x, y; }; struct PointCmp { bool operator()(const Point& lhs, const Point& rhs) const { return lhs.x < rhs.x; // NB. ignores y on purpose } }; template <typename Key, typename Value, typename Cmp> void println(auto rem, std::multimap<Key, Value, Cmp> const& map) { std::cout << rem << "{ "; for (auto n{map.size()}; auto const& p : map) std::cout << '[' << p.first << ":" << p.second << (--n ? "], " : "]"); std::cout << " }\n"; } int main() { std::multimap<int, int> m1 = { {1, 1}, {2, 2}, {3, 3}, {4, 4}, {4, 4}, {3, 3}, {2, 2}, {1, 1} }; println("m1 = ", m1); // Custom comparison std::multimap<Point, double, PointCmp> mag { {{5, 12}, 13}, {{3, 4}, 5}, {{8, 15}, 17}, {{3, -3}, -1} }; for (auto p : mag) std::cout << "The magnitude of (" << p.first.x << ", " << p.first.y << ")" " is " << p.second << '\n'; std::cout << "Construction from a range:\n"; using PS = std::pair<int, std::string>; const auto rg = {PS{3, "Earth"}, {2, "Venus"}, {1, "Mercury"}, {3, "Moon"}}; #if __cpp_lib_containers_ranges std::multimap<int, std::string> m2(std::from_range, rg); // over- load (12) #else std::multimap<int, std::string> m2(rg.begin(), rg.end()); // fall- back to (4) #endif println("m2 = ", m2); } Output: m1 = { [1:1], [1:1], [2:2], [2:2], [3:3], [3:3], [4:4], [4:4] } The magnitude of (3, 4) is 5 The magnitude of (3, -3) is -1 The magnitude of (5, 12) is 13 The magnitude of (8, 15) is 17 Construction from a range: m2 = { [1:Mercury], [2:Venus], [3:Earth], [3:Moon] } Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior LWG 2076 C++11 overload (4) conditionally required Keyand T not required to be CopyInsertable into *this LWG 2193 C++11 the default constructor was explicit made non-explicit See also operator= assigns values to the container (public member function) http://cppreference.com 2024.06.10 std::multimap::multimap(3)
NAME | Synopsis | Parameters | Type requirements | Complexity | Exceptions | Notes | Example | Output: | See also
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