std::vector::insert(3)

🌈 std::vector::insert(3) 🌈

okay bestie, welcome to the C++ Standard Libary — yes, this page is literally about std::vector::insert, and it's giving main-character energy. 💅

💖 NAME 💖

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

🌟 Synopsis 🌟

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

Inserts elements at the specified location in the container. 🫶

• 1,2) Inserts value before pos.
• 3) Inserts count copies of value before pos.
• 4) Inserts elements from range [first, last) before pos.
• 5) Inserts elements from initializer list ilist before pos.

For overload (4), bestie, listen:

• (until C++11) This overload has the same effect as overload (3) if InputIt is an integral type.
• (since C++11) This overload participates in overload resolution only if InputIt qualifies as LegacyInputIterator, to avoid ambiguity with overload (3).

🚨 If first and last are iterators into *this, the behavior is undefined. Not cute, not allowed, no cap.

Also important, and I cannot stress this enough: if after the operation the new size() is greater than old capacity() a reallocation takes place, in which case all iterators (including the end() iterator) and all 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 overloads (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 overloads (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,

these functions have no effect (strong exception safety guarantee). 🛡️

(since C++11) 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.

🍓 Example 🍓

bestie, run this code:

// 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. glow-ups but make it standards committee 💅

• LWG 149, applied to C++98 — behavior as published: overloads (3) and (4) returned nothing; correct behavior: returns an iterator.
• LWG 247, applied to C++98 — behavior as published: the complexity was only specified for overload (3); correct behavior: specified for all overloads.
• LWG 406, applied to C++98 — behavior as published: the strong exception guarantee also applied if the exception is thrown by an InputIt operation; correct behavior: no guarantee in this case.

👑 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)

---

sign-off, bestie: source is http://cppreference.com, version/date is 2024.06.10, and this iconic page is std::vector::insert(3) 🫶✨