std::deque::insert(3)

NAME
std::deque::insert - std::deque::insert

Synopsis
   iterator insert( iterator pos, const T& value ); (until
                        C++11)
   iterator insert( const_iterator pos, const T& value (since
   ); C++11)
   iterator insert( const_iterator pos, T&& value ); (2) (since
                        C++11)
   void insert( iterator pos, size_type count, const T& (until
   value ); C++11)
   iterator insert( const_iterator pos, size_type (since
   count, const T& value ); (1) C++11)
   template< class InputIt > (until
   void insert( iterator pos, InputIt first, InputIt C++11)
   last ); (3)
   template< class InputIt >
                        (4) (since
   iterator insert( const_iterator pos, C++11)
   InputIt first, InputIt last );
   iterator insert( const_iterator pos, (5) (since
   std::initializer_list<T> ilist ); C++11)
   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.
   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 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 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 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 lesser of the distances between pos and either of
   the ends of the container.
   3) Linear in count plus linear in the lesser of the distances between pos and either
   of the ends of the container.
   4) Linear in std::distance(first, last) plus linear in the lesser of the distances
   between pos and either of the ends of the container.
   5) Linear in ilist.size() plus linear in the lesser of the distances between pos and
   either of the ends of the container.

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

Example
// Run this code
 #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);
 }

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_front inserts an element to the beginning
              (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)