std::vector::insert(3)

NAME
std::vector::insert - std::vector::insert

Synopsis
   iterator insert( iterator pos, const (until
   T& value ); C++11)
                        (since
   iterator insert( const_iterator pos, C++11)
   const T& value ); (until
                        C++20)
   constexpr iterator insert( (since
   const_iterator pos, const T& value C++20)
   );
                        (since
   iterator insert( const_iterator pos, C++11)
   T&& value ); (until
                        C++20)
   constexpr iterator insert( (since
   const_iterator pos, T&& value ); C++20)
   void insert( iterator pos, size_type (until
   count, const T& value ); C++11)
                        (since
   iterator insert( const_iterator pos, C++11)
   size_type count, const T& value ); (until
                        C++20)
   constexpr iterator insert( (since
   const_iterator pos, size_type count, (1) C++20)
   const T& value );
   template< class InputIt > (until
   void insert( iterator pos, InputIt C++11)
   first, InputIt last ); (2)
   template< class InputIt > (since
                        C++11)
   iterator insert( const_iterator pos, (3) (until
                        C++20)
   InputIt first, InputIt last );
   template< class InputIt >
   constexpr iterator insert( (4) (since
   const_iterator pos, C++20)
   InputIt first, InputIt last );
                        (since
   iterator insert( const_iterator pos, C++11)
   std::initializer_list<T> ilist ); (until
                        (5) C++20)
   constexpr iterator insert( (since
   const_iterator pos, C++20)
   std::initializer_list<T> ilist );
   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.
   This overload has the same effect as overload (3) if InputIt is an (until C++11)
   integral type.
   This overload participates in overload resolution only if InputIt
   qualifies as LegacyInputIterator, to avoid ambiguity with the overload (since C++11)
   (3).
   The behavior is undefined if first and last are iterators into *this.
   5) inserts elements from initializer list ilist before pos.
   Causes reallocation if the new size() is greater than the old capacity(). 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
                        the range of elements to insert, can't be
   first, last - iterators into container for which insert is
                        called
   ilist - initializer list to insert the values from

Type requirements
   -
   T must meet the requirements of CopyAssignable and CopyInsertable in order to use
   overload (1).
   -
   T must meet the requirements of MoveAssignable and MoveInsertable in order to use
   overload (2).
   -
   T must meet the requirements of CopyAssignable and CopyInsertable in order to use
   overload (3).
   -
   T must meet the requirements of EmplaceConstructible in order to use overload (4,5).
   -
   T must meet the requirements of MoveAssignable and MoveInsertable in order to use
   overload (4). required only if InputIt satisfies LegacyInputIterator but not
   LegacyForwardIterator. (until C++17)
   -
   T must meet the requirements of Swappable, MoveAssignable, MoveConstructible and
   MoveInsertable in order to use overload (4,5). (since C++17)

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.
   3) Linear in count plus linear in the distance between pos and end of the container.
   4) Linear in std::distance(first, last) plus linear in the distance between pos and
   end of the container.
   5) Linear in ilist.size() plus linear in the distance between pos and end of the
   container.

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
// Run this code
 #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

See also
   emplace constructs element in-place
   (C++11) (public member function)
   push_back adds an element to the end
             (public member function)
   inserter creates a std::insert_iterator of type inferred from the argument
             (function template)