std::vector insert() method

od C++20

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

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

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

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

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

od C++11

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

do C++11

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

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

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

Inserts elements at the specified location in the container.

• (1-2) Inserts value before pos.

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

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

  od C++11

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

  do C++11

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

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

Reallocation

Causes reallocation if the new size() is greater than the old capacity().

Invalidation

If the new size() is greater than capacity(), all iterators and references are invalidated.

Otherwise, only the iterators and references before the insertion point remain valid.

The past-the-end iterator is also 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 elements to insert
• first, last - the range of elements to insert, can't be iterators into container for which insert is called
• ilist - initializer list to insert the values from

Type requirements

T is the container's element type in all the requirements below.

• (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

• od C++17

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

  do C++17

  (4) If InputIt satisfies LegacyInputIterator: T must meet the requirements of MoveAssignable 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

• (1-2) Constant plus linear in the distance between pos and end of the container - O(std::distance(pos, end())).
• (3) Linear in count plus linear in the distance between pos and end of the container - O(count + std::distance(pos, end())).
• (4) Linear in std::distance(first, last) plus linear in the distance between pos and end of the container - O(std::distance(first, last) + std::distance(pos, end())).
• (5) Linear in ilist.size() plus linear in the distance between pos and end of the container - O(ilist.size() + std::distance(pos, end())).

Exceptions

If an exception is thrown when inserting a single element at the end, and T is CopyInsertable or std::is_nothrow_move_constructible<T>::value is true, there are no effects (strong exception guarantee).

Example

Main.cpp

#include <iostream>
#include <iterator>
#include <vector>
 
void print(int id, const std::vector<int>& container)
{
    std::cout << id << ". ";
    for (const int x: container) {
         std::cout << x << ' ';
    }
    std::cout << '\n';
}
 
int main ()
{
    std::vector<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);
 
    // `it` no longer valid, get a new one:
    it = c1.begin();
 
    std::vector<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);
}

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