# std::vector<T,Allocator>::insert

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< cpp‎ | container‎ | vector

| (1) |
iterator insert( const_iterator pos, const T& value ); |  | (until C++20)
constexpr iterator insert( const_iterator pos, const T& value ); |  | (since C++20)
| (2) |
iterator insert( const_iterator pos, T&& value ); |  | (since C++11) (until C++20)
constexpr iterator insert( const_iterator pos, T&& value ); |  | (since C++20)
| (3) |
iterator insert( const_iterator pos, size_type count, const T& value ); |  | (until C++20)
constexpr iterator insert( const_iterator pos, size_type count, const T& value ); |  | (since C++20)
| (4) |
template< class InputIt > iterator insert( const_iterator pos, InputIt first, InputIt last ); |  | (until C++20)
template< class InputIt > constexpr iterator insert( const_iterator pos, InputIt first, InputIt last ); |  | (since C++20)
| (5) |
iterator insert( const_iterator pos, std::initializer_list<T> ilist ); |  | (since C++11) (until C++20)
constexpr iterator insert( const_iterator pos, std::initializer_list<T> ilist ); |  | (since C++20)

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 integral type. | (until C++11)
This overload participates in overload resolution only if `InputIt` qualifies as LegacyInputIterator, to avoid ambiguity with the overload (3). | (since C++11)

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 new size() is greater than capacity() the function causes reallocation, in which case all iterators (including the end() iterator) and references to the elements are invalidated. Otherwise, only the iterators and references before the insertion point remain valid.

### 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, cannot 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 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 other than by

- the copy constructor of `T`,

the move constructor of `T`, | (since C++11)

- the copy assignment operator of `T`,

the move assignment operator of `T`, | (since C++11)

- any `InputIt` operation,

this function has no effect (strong exception guarantee).

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, this function has no effect (strong exception guarantee). Otherwise, if an exception is thrown by the move constructor of a non-CopyInsertable `T`, the effects are unspecified. | (since C++11)

### 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

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 149 | C++98 | overloads (3) and (4) returned nothing | returns an iterator
LWG 247 | C++98 | the complexity was only specified for overload (3) | specified for all overloads
LWG 406 | C++98 | the strong exception guarantee also applied if the exception is thrown by an `InputIt` operation | no guarantee in this case

### See also

emplace (C++11) | constructs element in-place (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)

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