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std::set::set(3) C++ Standard Libary std::set::set(3) NAME std::set::set - std::set::set Synopsis set(); explicit set( const Compare& comp, const Allocator& alloc = Allocator() ); explicit set( const Allocator& alloc ); (1) (since C++11) template< class InputIt > set( InputIt first, InputIt last, const Compare& comp = Compare(), const Allocator& alloc = Allocator() ); template< class InputIt > set( InputIt first, InputIt last, const Allocator& (since alloc) C++14) : set(first, last, Compare(), alloc) {} set( const set& other ); (3) set( const set& other, const Allocator& alloc ); (2) (3) (since C++11) set( set&& other ); (4) (since C++11) set( set&& other, const Allocator& alloc ); (4) (since C++11) set( std::initializer_list<value_type> init, (since const Compare& comp = Compare(), C++11) (5) const Allocator& alloc = Allocator() ); set( std::initializer_list<value_type> init, const (since Allocator& alloc ) C++14) : set(init, 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) Default constructor. Constructs empty container. 2) Range constructor. Constructs the container with the contents of the range [first, last). If multiple elements in the range have keys that com- pare equivalent, it is unspecified which element is inserted (pending LWG2844). 3) 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>::select_on_container_copy_con- struction( C++11) other.get_allocator()). The template parameter Allocator is only deduced from the first ar- gument (since while used in class template argument deduction. C++23) 4) 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. The template parameter Allocator is only deduced from the first (since C++23) argument while used in class template argument deduction. 5) Initializer-list constructor. Constructs the container with the contents of the initializer list init. If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending LWG2844). 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 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) Constant 2) N log(N) where N = std::distance(first, last) in general, linear in N if the range is already sorted by value_comp(). 3) Linear in size of other 4) Constant. If alloc is given and alloc != other.get_allocator(), then linear. 5) N log(N) where N = init.size() in general, linear in N if init is already sorted by value_comp(). Exceptions Calls to Allocator::allocate may throw. Notes After container move construction (overload (4)), references, point- ers, 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.requirements.general]/12, and a more direct guarantee is under consideration via LWG 2321. Although not formally required until C++23, some implementations has already put the template parameter Allocator into non-deduced contexts in earlier modes. Example // Run this code #include <iostream> #include <string> #include <set> #include <cmath> struct Point { double x, y; }; struct PointCmp { bool operator()(const Point& lhs, const Point& rhs) const { return std::hypot(lhs.x, lhs.y) < std::hypot(rhs.x, rhs.y); } }; int main() { // (1) Default constructor std::set<std::string> a; a.insert("cat"); a.insert("dog"); a.insert("horse"); for(auto& str: a) std::cout << str << ' '; std::cout << '\n'; // (2) Iterator constructor std::set<std::string> b(a.find("dog"), a.end()); for(auto& str: b) std::cout << str << ' '; std::cout << '\n'; // (3) Copy constructor std::set<std::string> c(a); c.insert("another horse"); for(auto& str: c) std::cout << str << ' '; std::cout << '\n'; // (4) Move constructor std::set<std::string> d(std::move(a)); for(auto& str: d) std::cout << str << ' '; std::cout << '\n'; std::cout << "moved-from set is "; for(auto& str: a) std::cout << str << ' '; std::cout << '\n'; // (5) Initializer list constructor std::set<std::string> e {"one", "two", "three", "five", "eight"}; for(auto& str: e) std::cout << str << ' '; std::cout << '\n'; // custom comparison std::set<Point, PointCmp> z = {{2, 5}, {3, 4}, {1, 1}}; z.insert({1, -1}); // this fails because the magnitude of 1,-1 equals 1,1 for(auto& p: z) std::cout << '(' << p.x << ',' << p.y << ") "; std::cout << '\n'; } Output: cat dog horse dog horse another horse cat dog horse cat dog horse moved-from set is eight five one three two (1,1) (3,4) (2,5) Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct be- havior LWG 2193 C++11 the default constructor is explicit made non-ex- plicit See also operator= assigns values to the container (public member function) http://cppreference.com 2022.07.31 std::set::set(3)
NAME | Synopsis | Parameters | Type requirements | Complexity | Exceptions | Notes | Example | Output: | See also
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