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 hint, const value_type& (until C++11)
   value );
   iterator insert( const_iterator hint, const (since C++11)
   value_type& value );
   iterator insert( const_iterator hint, value_type&& (4) (since C++11)
   value );
   template< class InputIt > (3) (5)
   void insert( InputIt first, InputIt last );
   void insert( std::initializer_list<value_type> ilist (6) (since C++11)
   );
   insert_return_type insert( node_type&& nh ); (7) (since C++17)
   iterator insert( const_iterator hint, node_type&& nh (8) (since C++17)
   );
   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, just prior(since C++11), to
   hint.
   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 hint. The behavior is undefined if
   nh is not empty and get_allocator() != nh.get_allocator().
   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
                 iterator, used as a suggestion as to where to start the (until C++11)
   hint - search
                 iterator to the position before which the new element (since C++11)
                 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

Type requirements
   -
   InputIt must meet the requirements of LegacyInputIterator.

Return value
   1-2) Returns 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 the insertion
   took place.
   3-4) Returns an iterator to the inserted element, or to the element that prevented
   the insertion.
   5-6) (none)
   7) Returns an 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.

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

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 (until C++11)
   after the hint, logarithmic in the size of the container otherwise.
   3-4) Amortized constant if the insertion happens in the position just (since C++11)
   before the hint, 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 the hint,
   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 set) whose smallest element is greater than the last element in *this

Example
// Run this code
 #include <set>
 #include <cassert>
 #include <iostream>
 int main()
 {
   std::set<int> set;
   auto result_1 = set.insert(3);
   assert(result_1.first != set.end()); // it's 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

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)