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# std::vector::insert

From cppreference.com
< cpp‎ | container‎ | vector

[edit template]

| (1) |
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)
| (3) |
void insert( iterator pos, size_type count, const T& value ); |  | (until C++11)
iterator insert( const_iterator pos, size_type count, const T& value ); |  | (since C++11)
| (4) |
template< class InputIt > void insert( iterator pos, InputIt first, InputIt last); |  | (until C++11)
template< class InputIt > iterator insert( const_iterator pos, InputIt first, InputIt last ); |  | (since C++11)
iterator insert( const_iterator pos, std::initializer_list<T> ilist ); | (5) | (since C++11)

Inserts elements at specified location in the container.

1-2) inserts `value` before the location pointed to by `pos`
3) inserts `count` copies of the `value` before the location pointed to by `pos`
4) inserts elements from range `[first, last)` before the location pointed to by `pos`. The behavior is undefined if `first` and `last` are iterators into *this.
5) inserts elements from initializer list `ilist`.

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.

### [edit] Parameters

pos | - | iterator to the location before which the content will be inserted. `pos` may be the end() iterator
value | - | element value 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
- `InputIt` must meet the requirements of `InputIterator`.

### [edit] 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.

### [edit] 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.

### Example

Run this code

    #include <iostream>
    #include <vector>

    void print_vec(const std::vector<int>& vec)
    {
        for (auto x: vec) {
             std::cout << ' ' << x;
        }
        std::cout << '\n';
    }

    int main ()
    {
        std::vector<int> vec(3,100);
        print_vec(vec);

        auto it = vec.begin();
        it = vec.insert(it, 200);
        print_vec(vec);

        vec.insert(it,2,300);
        print_vec(vec);

        // "it" no longer valid, get a new one:
        it = vec.begin();

        std::vector<int> vec2(2,400);
        vec.insert(it+2, vec2.begin(), vec2.end());
        print_vec(vec);

        int arr[] = { 501,502,503 };
        vec.insert(vec.begin(), arr, arr+3);
        print_vec(vec);
    }

Output:

    100 100 100
    200 100 100 100
    300 300 200 100 100 100
    300 300 400 400 200 100 100 100
    501 502 503 300 300 400 400 200 100 100 100

### [edit] See also

emplace (C++11) | constructs element in-place (public member function) [edit]
push_back | adds elements to the end (public member function) [edit]

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