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# std::set::insert

From cppreference.com
< cpp‎ | container‎ | set

std::pair<iterator,bool> insert( const value_type& value ); | (1) |
std::pair<iterator,bool> insert( value_type&& value ); | (2) | (since C++11)
| (3) |
iterator insert( iterator hint, const value_type& value ); |  | (until C++11)
iterator insert( const_iterator hint, const value_type& value ); |  | (since C++11)
iterator insert( const_iterator hint, value_type&& value ); | (4) | (since C++11)
template< class InputIt > void insert( InputIt first, InputIt last ); | (5) |
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)

### [edit] Parameters

hint | - |
iterator, used as a suggestion as to where to start the search | (until C++11)
iterator to the position before which the new element will be inserted | (since C++11)
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 `InputIterator`.

### [edit] 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.

### [edit] Exceptions

1-4) If an exception is thrown by any operation, the insertion has no effect.

| This section is incomplete Reason: cases 5-8

### [edit] 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 the hint, logarithmic in the size of the container otherwise. | (until C++11)
3-4) Amortized constant if the insertion happens in the position just before the hint, logarithmic in the size of the container otherwise. | (since C++11)

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.

### [edit] 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

### [edit] 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

### [edit] See also

emplace (C++11) | constructs element in-place (public member function) [edit]
emplace_hint (C++11) | constructs elements in-place using a hint (public member function) [edit]

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