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

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< cpp‎ | container‎ | list

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

No iterators or references are 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, 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 CopyInsertable in order to use overload (1).
- `T` must meet the requirements of 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).

### 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.
3) Linear in count
4) Linear in std::distance(first, last)
5) Linear in ilist.size()

### Exceptions

If an exception is thrown for any reason, these functions have no effect (strong exception safety guarantee).

### Example

Run this code

    #include <iostream>
    #include <iterator>
    #include <list>

    void print(int id, const std::list<int>& container)
    {
        std::cout << id << ". ";
        for (const int x: container)
            std::cout << x << ' ';
        std::cout << '\n';
    }

    int main ()
    {
        std::list<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::list<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

### See also

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

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