NAME¶

std::flat_set::insert - std::flat_set::insert

Synopsis¶

std::pair<iterator, bool> insert( const value_type& value ); (1) (since C++23)
std::pair<iterator, bool> insert( value_type&& value ); (2) (since C++23)
iterator insert( const_iterator pos, const value_type& value ); (3) (since C++23)
iterator insert( const_iterator pos, value_type&& value ); (4) (since C++23)
template< class K > (5) (since C++23)
iterator insert( const_iterator pos, K&& x );
template< class InputIt > (6) (since C++23)
void insert( InputIt first, InputIt last );
template< class K > (7) (since C++23)
std::pair<iterator, bool> insert( K&& x );
template< class InputIt > (8) (since C++23)
void insert( std::sorted_unique_t, InputIt first, InputIt last );
void insert( std::initializer_list<key_type> ilist ); (9) (since C++23)
void insert( std::sorted_unique_t s, (10) (since C++23)
std::initializer_list<key_type> ilist );

Inserts element(s) into the container, if the container does not already contain an
element with an equivalent key.

1) Inserts value. Equivalent to return emplace(value);.
2) Inserts value. Equivalent to return emplace(std::move(value));.
3) Inserts value in the position as close as possible to the position just prior to
pos. Equivalent to return emplace_hint(pos, value);.
4) Inserts value in the position as close as possible to the position just prior to
pos. Equivalent to return emplace_hint(pos, std::move(value));.
5,7) If *this already contains an element which transparently compares equivalent to
x, does nothing. Otherwise, inserts a new element as if by:
* (5) emplace(pos, std::forward<K>(x)) (in the position as close as possible to
the position just prior to pos);
* (7) emplace(std::forward<K>(x)).
The conversion from x into key_type must construct an object u, for which find(k) ==
find(u) is true. Otherwise, the behavior is undefined.
These overloads participate in overload resolution only if
* The qualified-id Compare::is_transparent is valid and denotes a type, and
* std::is_constructible_v<value_type, K> is true,
which together allows calling this function without constructing an instance of Key.
6) Equivalent to the sequence of operations:
1. Inserts elements from range [first, last) as if by c.insert(c.end(), first,
last);.
2. Sorts the range of newly inserted elements with respect to compare.
3. Merges the resulting sorted range and the sorted range of pre-existing elements
into a single sorted range. (Note: the merge operation may allocate memory).
4. Erases all but the first element from each group of consecutive equivalent
elements.
If multiple elements in the range have keys that compare equivalent, it is
unspecified which element is inserted (pending LWG2844).
8) Inserts elements from range [first, last). Equivalent to insert(first, last);.
If multiple elements in the range have keys that compare equivalent, it is
unspecified which element is inserted (pending LWG2844).
9) Inserts elements from initializer list ilist. Equivalent to insert(ilist.begin(),
ilist.end());.
If multiple elements in the range have keys that compare equivalent, it is
unspecified which element is inserted (pending LWG2844).
10) Inserts elements from initializer list ilist. Equivalent to insert(s,
ilist.begin(), ilist.end());.
If multiple elements in the range have keys that compare equivalent, it is
unspecified which element is inserted (pending LWG2844).

Information on iterator invalidation is copied from here

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
x - a value of any type that can be transparently compared with a key
s - a disambiguation tag indicating that the input sequence is sorted
(with respect to compare) and contains only unique elements

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.
3-5) An iterator to the inserted element, or to the element that prevented the
insertion.
6) (none)
7) 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.
8-10) (none)

Exceptions¶

1-5,7) If an exception is thrown by any operation, the insertion has no effect.

This section is incomplete
Reason: cases 6,8-10

Complexity¶

1-5) Linear in size().
6) N + M·log(M), where N is the size() before the operation and M is
std::distance(first, last).
7) Linear in size().
8) Linear in N, where N is size() after the operation.
9) N + M·log(M), where N is the size() before the operation and M is ilist.size().
10) Linear in N, where N is size() after the operation.

This section is incomplete
Reason: recheck the complexity: 1-5, 7, 9, 10. The lookup is log(N), but insertion
in underlying container is N/2 on average => Linear.

Notes¶

The hinted insert (3-5) 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 <cassert>
#include <flat_set>
#include <iostream>

int main()
{
std::flat_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); // the 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
(public member function)
emplace_hint constructs elements in-place using a hint
(public member function)
inserter creates a std::insert_iterator of type inferred from the argument
(function template)

Category:¶

* Todo with reason