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 optionally 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 compare 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_construction( C++11)
   other.get_allocator()).
   The template parameter Allocator is only deduced from the first argument (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, 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.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 retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 2193 C++11 the default constructor is explicit made non-explicit

See also
   operator= assigns values to the container
             (public member function)