std::deque insert() method

since C++11

// (1) Non const version only
iterator insert( const_iterator pos, const T& value );

// (2) Non const version only
iterator insert( const_iterator pos, T&& value );

// (3) Non const version only
iterator insert( const_iterator pos, size_type count, const T& value );

// (4) Non const version only
template< class InputIt >
iterator insert( const_iterator pos, InputIt first, InputIt last );

// (5) Non const version only
iterator insert( const_iterator pos, std::initializer_list<T> ilist );

until C++11

// (1) Non const version only
iterator insert( iterator pos, const T& value );

// (3) Non const version only
void insert( iterator pos, size_type count, const T& value );

// (4) Non const version only
template< class InputIt >
void insert( iterator pos, InputIt first, InputIt last );

Inserts element(s) into the container, if the container doesn't already contain an element with an equivalent key.

• (1-2) Inserts value before pos.

• (3) Inserts count copies of the value before pos.

• (4) Inserts elements from range [ first; last ) before pos.

  since C++11

  This overload participates in overload resolution only if InputIt qualifies as LegacyInputIterator, to avoid ambiguity with the overload (3).

  until C++11

  This overload has the same effect as overload (3) if InputIt is an integral type.

  Undefined behaviour

  The behavior is undefined if first and last are iterators into *this.

• (5) Inserts elements from initializer list ilist before pos.

  Undefined behaviour

  All iterators, including the past-the-end iterator, are invalidated. References are invalidated too, unless pos == begin() or pos == end(), in which case they are not invalidated.

Parameters

• pos - iterator before which the content will be inserted. pos may be the end() iterator
• value - element value to insert
• count - number of elemnts to insert
• first, last - range of elements to insert
• ilist - initializer list to insert the values from

Type requirements

• (1) - T must meet the requirements of CopyAssignable and CopyInsertable.
• (2) - T must meet the requirements of MoveAssignable and MoveInsertable.
• (3) - T must meet the requirements of CopyAssignable and CopyInsertable.
• (4-5) - T must meet the requirements of EmplaceConstructible.
• since C++17

  (4-5) - T must meet the requirements of Swappable, MoveAssignable, MoveConstructible and MoveInsertable.

Return value

• (1-2) Iterator pointing to the inserted value.
• (3) Iterator pointing to the first element inserted, or pos if count == 0.
• (4) Iterator pointing to the first element inserted, or pos if first == last.
• (5) Iterator pointing to the first element inserted, or pos if ilist is empty.

Complexity

For all of the below N is std::min(std::distance(pos, begin()), std::distance(pos, end()))

• (1-2) Linear in the lesser of the distances between pos and either of the ends of the container - O(N).
• (3) Linear in count + linear in the lesser of the distances between pos and either of the ends of the container - O(count + N).
• (4) Linear in std::distance(first, last) + linear in the lesser of the distances between pos and either of the ends of the container - O(std::distance(first, last) + N).
• (5) Linear in ilist.size() + linear in the lesser of the distances between pos and either of the ends of the container - O(ilist.size() + N).

Exceptions

If an exception is thrown when inserting a single element at either end, this function has no effect (strong exception guarantee).

Example

Main.cpp

#include <iostream>
#include <iterator>
#include <deque>

void print(int id, const std::deque<int>& container)
{
    std::cout << id << ". ";
    for (const int x: container)
        std::cout << x << ' ';
    std::cout << '\n';
}

int main ()
{
    std::deque<int> c1(3, 100);
    print(1, c1);

    auto it = c1.begin();
    it = c1.insert(it, 200);
    print(2, c1);

    c1.insert(it, 2, 300);
    print(3, c1);

    // reset `it` to the begin:
    it = c1.begin();

    std::deque<int> c2(2, 400);
    c1.insert(std::next(it, 2), c2.begin(), c2.end());
    print(4, c1);

    int arr[] = {501, 502, 503};
    c1.insert(c1.begin(), arr, arr + std::size(arr));
    print(5, c1);

    c1.insert(c1.end(), {601, 602, 603});
    print(6, c1);
}

Possible output

1. 100 100 100
2. 200 100 100 100
3. 300 300 200 100 100 100
4. 300 300 400 400 200 100 100 100
5. 501 502 503 300 300 400 400 200 100 100 100
6. 501 502 503 300 300 400 400 200 100 100 100 601 602 603