std::map::insert(3)

NAME
std::map::insert - std::map::insert

Synopsis
   std::pair<iterator, bool> insert( const value_type& (1)
   value );
   template< class P > (2) (since C++11)
   std::pair<iterator, bool> insert( P&& value );
   std::pair<iterator, bool> insert( value_type&& value (3) (since C++17)
   );
   iterator insert( iterator pos, const value_type& (until C++11)
   value );
   iterator insert( const_iterator pos, const (since C++11)
   value_type& value );
   template< class P > (5) (since C++11)
   iterator insert( const_iterator pos, P&& value );
   iterator insert( const_iterator pos, value_type&& (6) (since C++17)
   value ); (4)
   template< class InputIt > (7)
   void insert( InputIt first, InputIt last );
   void insert( std::initializer_list<value_type> ilist (8) (since C++11)
   );
   insert_return_type insert( node_type&& nh ); (9) (since C++17)
   iterator insert( const_iterator pos, node_type&& nh (10) (since C++17)
   );
   Inserts element(s) into the container, if the container doesn't already contain an
   element with an equivalent key.
   1-3) Inserts value.
   Overload (2) is equivalent to emplace(std::forward<P>(value)) and only participates
   in overload resolution if std::is_constructible<value_type, P&&>::value == true.
   4-6) Inserts value in the position as close as possible to the position just prior
   to pos.
   Overload (5) is equivalent to emplace_hint(hint, std::forward<P>(value)) and only
   participates in overload resolution if std::is_constructible<value_type, P&&>::value
   == true.
   7) 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).
   8) 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).
   9) 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().
   10) 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().
   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

Type requirements
   -
   InputIt must meet the requirements of LegacyInputIterator.

Return value
   1-3) 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.
   4-6) An iterator to the inserted element, or to the element that prevented the
   insertion.
   7,8) (none)
   9) 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().
   10) 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
   1-6) If an exception is thrown by any operation, the insertion has no effect.
    This section is incomplete
    Reason: cases 7-10

Complexity
   1-3) Logarithmic in the size of the container, O(log(size())).
   4-6) 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.
   7,8) O(N·log(size() + N)), where N is the number of elements to insert.
   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 (4-6) 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.

Example
// Run this code
 #include <iomanip>
 #include <iostream>
 #include <map>
 #include <string>
 using namespace std::literals;
 template<typename It>
 void print_insertion_status(It it, bool success)
 {
     std::cout << "Insertion of " << it->first
               << (success ? " succeeded\n" : " failed\n");
 }
 int main()
 {
     std::map<std::string, float> heights;
     // Overload 3: insert from rvalue reference
     const auto [it_hinata, success] = heights.insert({"Hinata"s, 162.8});
     print_insertion_status(it_hinata, success);
     {
         // Overload 1: insert from lvalue reference
         const auto [it, success2] = heights.insert(*it_hinata);
         print_insertion_status(it, success2);
     }
     {
         // Overload 2: insert via forwarding to emplace
         const auto [it, success] = heights.insert(std::pair{"Kageyama", 180.6});
         print_insertion_status(it, success);
     }
     {
         // Overload 6: insert from rvalue reference with positional hint
         const std::size_t n = std::size(heights);
         const auto it = heights.insert(it_hinata, {"Azumane"s, 184.7});
         print_insertion_status(it, std::size(heights) != n);
     }
     {
         // Overload 4: insert from lvalue reference with positional hint
         const std::size_t n = std::size(heights);
         const auto it = heights.insert(it_hinata, *it_hinata);
         print_insertion_status(it, std::size(heights) != n);
     }
     {
         // Overload 5: insert via forwarding to emplace with positional hint
         const std::size_t n = std::size(heights);
         const auto it = heights.insert(it_hinata, std::pair{"Tsukishima", 188.3});
         print_insertion_status(it, std::size(heights) != n);
     }
     auto node_hinata = heights.extract(it_hinata);
     std::map<std::string, float> heights2;
     // Overload 7: insert from iterator range
     heights2.insert(std::begin(heights), std::end(heights));
     // Overload 8: insert from initializer_list
     heights2.insert({{"Kozume"s, 169.2}, {"Kuroo", 187.7}});
     // Overload 9: insert node
     const auto status = heights2.insert(std::move(node_hinata));
     print_insertion_status(status.position, status.inserted);
     node_hinata = heights2.extract(status.position);
     {
         // Overload 10: insert node with positional hint
         const std::size_t n = std::size(heights2);
         const auto it = heights2.insert(std::begin(heights2), std::move(node_hinata));
         print_insertion_status(it, std::size(heights2) != n);
     }
     // Print resulting map
     std::cout << std::left << '\n';
     for (const auto& [name, height] : heights2)
         std::cout << std::setw(10) << name << " | " << height << "cm\n";
 }

Output:
 Insertion of Hinata succeeded
 Insertion of Hinata failed
 Insertion of Kageyama succeeded
 Insertion of Azumane succeeded
 Insertion of Hinata failed
 Insertion of Tsukishima succeeded
 Insertion of Hinata succeeded
 Insertion of Hinata succeeded
 Azumane | 184.7cm
 Hinata | 162.8cm
 Kageyama | 180.6cm
 Kozume | 169.2cm
 Kuroo | 187.7cm
 Tsukishima | 188.3cm
   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 (7) 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
   LWG 2005 C++11 overloads (2,5) were poorly described improved the description

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)
   insert_or_assign inserts an element or assigns to the current element if the key
   (C++17) already exists
                    (public member function)
   inserter creates a std::insert_iterator of type inferred from the argument
                    (function template)

Category:
     * Todo with reason