std::set::insert(3)

NAME
std::set::insert - std::set::insert

Synopsis
   std::pair<iterator, bool> insert( const value_type& (1)
   value );
   std::pair<iterator, bool> insert( value_type&& value (2) (since C++11)
   );
   iterator insert( iterator pos, const value_type& (until C++11)
   value );
   iterator insert( const_iterator pos, const (since C++11)
   value_type& value );
   iterator insert( const_iterator pos, value_type&& (4) (since C++11)
   value );
   template< class InputIt > (5)
   void insert( InputIt first, InputIt last );
   void insert( std::initializer_list<value_type> ilist (3) (6) (since C++11)
   );
   insert_return_type insert( node_type&& nh ); (7) (since C++17)
   iterator insert( const_iterator pos, node_type&& nh (8) (since C++17)
   );
   template< class K > (9) (since C++23)
   std::pair<iterator, bool> insert( K&& x );
   template< class K > (10) (since C++23)
   iterator insert( const_iterator pos, K&& x );
   Inserts element(s) into the container, if the container doesn't already contain an
   element with an equivalent key.
   1,2) Inserts value.
   3,4) Inserts value in the position as close as possible to the position just prior
   to pos.
   5) Inserts elements from range [first, last). If multiple elements in the range have
   keys that compare equivalent, it is unspecified which element is inserted (pending
   LWG2844).
   6) Inserts elements from initializer list ilist. If multiple elements in the range
   have keys that compare equivalent, it is unspecified which element is inserted
   (pending LWG2844).
   7) If nh is an empty node handle, does nothing. Otherwise, inserts the element owned
   by nh into the container , if the container doesn't already contain an element with
   a key equivalent to nh.key(). The behavior is undefined if nh is not empty and
   get_allocator() != nh.get_allocator().
   8) If nh is an empty node handle, does nothing and returns the end iterator.
   Otherwise, inserts the element owned by nh into the container, if the container
   doesn't already contain an element with a key equivalent to nh.key(), and returns
   the iterator pointing to the element with key equivalent to nh.key()(regardless of
   whether the insert succeeded or failed). If the insertion succeeds, nh is moved
   from, otherwise it retains ownership of the element. The element is inserted as
   close as possible to the position just prior to pos. The behavior is undefined if nh
   is not empty and get_allocator() != nh.get_allocator().
   9) If *this already contains an element which transparently compares equivalent to
   x, does nothing. Otherwise, constructs an object u of the value_type with
   std::forward<K>(x) and then inserts u into *this. If equal_range(u) ==
   equal_range(x) is false, the behavior is undefined. The value_type must be
   EmplaceConstructible into set from std::forward<K>(x). This overload participates in
   overload resolution only if the qualified-id Compare::is_transparent is valid and
   denotes a type. It allows calling this function without constructing an instance of
   Key.
   10) If *this already contains an element which transparently compares equivalent to
   x, does nothing. Otherwise, constructs an object u of the value_type with
   std::forward<K>(x) and then inserts u into *this in the position as close as
   possible to the position just prior to pos. If equal_range(u) == equal_range(x) is
   false, the behavior is undefined. The value_type must be EmplaceConstructible into
   set from std::forward<K>(x). This overload participates in overload resolution only
   if:
     * std::is_convertible_v<K&&, const_iterator> and std::is_convertible_v<K&&,
       iterator> are both false, and
     * the qualified-id Compare::is_transparent is valid and denotes a type,
   which together allows calling this function without constructing an instance of Key.
   No iterators or references are invalidated.
   If the insertion is successful, pointers and references to the element obtained
   while it is held in the node handle are invalidated, and pointers and references
   obtained to that element before it was extracted become valid.
   (since C++17)

Parameters
   pos - iterator to the position before which the new element will be inserted
   value - element value to insert
   first, last - range of elements to insert
   ilist - initializer list to insert the values from
   nh - a compatible node handle
   x - a value of any type that can be transparently compared with a key

Type requirements
   -
   InputIt must meet the requirements of LegacyInputIterator.

Return value
   1,2) A pair consisting of an iterator to the inserted element (or to the element
   that prevented the insertion) and a bool value set to true if and only if the
   insertion took place.
   3,4) An iterator to the inserted element, or to the element that prevented the
   insertion.
   5,6) (none)
   7) An object of insert_return_type with the members initialized as follows:
     * If nh is empty, inserted is false, position is end(), and node is empty.
     * Otherwise if the insertion took place, inserted is true, position points to the
       inserted element, and node is empty.
     * If the insertion failed, inserted is false, node has the previous value of nh,
       and position points to an element with a key equivalent to nh.key().
   8) End iterator if nh was empty, iterator pointing to the inserted element if
   insertion took place, and iterator pointing to an element with a key equivalent to
   nh.key() if it failed.
   9) A pair consisting of an iterator to the inserted element (or to the element that
   prevented the insertion) and a bool value set to true if and only if the insertion
   took place.
   10) An iterator to the inserted element, or to the element that prevented the
   insertion.

Exceptions
   1-4) If an exception is thrown by any operation, the insertion has no effect.
    This section is incomplete
    Reason: cases 5-8, 9, 10

Complexity
   1,2) Logarithmic in the size of the container, O(log(size())).
   3,4) Amortized constant if the insertion happens in the position just
   after
   (until C++11)
   before
   (since C++11) pos, logarithmic in the size of the container otherwise.
   5,6) O(N·log(size() + N)), where N is the number of elements to insert.
   7) Logarithmic in the size of the container, O(log(size())).
   8) Amortized constant if the insertion happens in the position just before pos,
   logarithmic in the size of the container otherwise.
   9) Logarithmic in the size of the container, O(log(size())).
   10) Amortized constant if the insertion happens in the position just before pos,
   logarithmic in the size of the container otherwise.

Notes
   The hinted insert (3,4) does not return a boolean in order to be
   signature-compatible with positional insert on sequential containers, such as
   std::vector::insert. This makes it possible to create generic inserters such as
   std::inserter. One way to check success of a hinted insert is to compare size()
   before and after.
   The overloads (5,6) are often implemented as a loop that calls the overload (3) with
   end() as the hint; they are optimized for appending a sorted sequence (such as
   another std::set) whose smallest element is greater than the last element in *this.
                Feature-test macro Value Std Feature
                        Heterogeneous
                        overloads for the
                        remaining member
   __cpp_lib_associative_heterogeneous_insertion 202311L (C++26) functions in ordered
                        and unordered
                        associative
                        containers. (9,10)

Example
// Run this code
 #include <cassert>
 #include <iostream>
 #include <set>
 int main()
 {
     std::set<int> set;
     auto result_1 = set.insert(3);
     assert(result_1.first != set.end()); // it is a valid iterator
     assert(*result_1.first == 3);
     if (result_1.second)
         std::cout << "insert done\n";
     auto result_2 = set.insert(3);
     assert(result_2.first == result_1.first); // same iterator
     assert(*result_2.first == 3);
     if (!result_2.second)
         std::cout << "no insertion\n";
 }

Output:
 insert done
 no insertion
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
     DR Applied to Behavior as published Correct behavior
                        the insertion is required
                      pos was just a hint, it could be to
   LWG 233 C++98 totally ignored be as close as possible to
                        the
                        position just prior to pos
                      the complexity of overload (5) was removed the linear
   LWG 264 C++98 required to be linear if requirement
                      the range [first, last) is sorted in this special case
                      according to Compare
                      in the return value of overload (1),
   LWG 316 C++98 it was not specified success is
                      which bool value indicates a indicated by true
                      successful insertion

See also
   emplace constructs element in-place
   (C++11) (public member function)
   emplace_hint constructs elements in-place using a hint
   (C++11) (public member function)
   inserter creates a std::insert_iterator of type inferred from the argument
                (function template)

Category:
     * Todo with reason