std::multimap<Key,T,Compare,Allocator>::multimap - cppreference.com (original) (raw)

Constructs new container from a variety of data sources and optionally 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) Constructs the container with the copy of the contents of other.

8,9) 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.

10,11) Constructs the container with the contents of the initializer list init.

12,13) Constructs the container with the contents of rg.

Contents

• 1 Parameters
• 2 Complexity
• 3 Exceptions
• 4 Notes
• 5 Example
• 6 Defect reports
• 7 See also

[edit] Parameters

[edit] Complexity

1-3) Constant.

4,5) \(\scriptsize N \cdot log(N)\)N·log(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) \(\scriptsize N \cdot log(N)\)N·log(N) where \(\scriptsize N\)N is init.size() in general, linear in \(\scriptsize N\)N if init is already sorted by value_comp().

12,13) \(\scriptsize N \cdot log(N)\)N·log(N) where \(\scriptsize N\)N is ranges::distance(rg) in general, linear in \(\scriptsize N\)N if rg is already sorted by value_comp().

[edit] Exceptions

Calls to Allocator::allocate may throw.

[edit] 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.

[edit] Example

#include #include #include   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, const std::multimap<Key, Value, Cmp>& map) { std::cout << rem << "{ "; for (auto n{map.size()}; const auto& 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); // overload (12) #else std::multimap<int, std::string> m2(rg.begin(), rg.end()); // fallback 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] }

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also