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.

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

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)

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.

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.

Example

#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";
}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also