std::vector源码

`std::vector`是C++标准库中的一个容器，用于存储动态大小的数组。下面是`std::vector`的简化源码：

template<typename T, typename Allocator = std::allocator<T>>
class vector {
public:
    using value_type = T;
    using allocator_type = Allocator;
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;
    using reference = value_type&;
    using const_reference = const value_type&;
    using pointer = typename std::allocator_traits<Allocator>::pointer;
    using const_pointer = typename std::allocator_traits<Allocator>::const_pointer;
    using iterator = pointer;
    using const_iterator = const_pointer;
    using reverse_iterator = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;

    // 构造函数
    vector() noexcept;
    explicit vector(const Allocator& alloc) noexcept;
    explicit vector(size_type count, const T& value, const Allocator& alloc = Allocator());
    explicit vector(size_type count, const Allocator& alloc = Allocator());
    template<typename InputIt>
    vector(InputIt first, InputIt last, const Allocator& alloc = Allocator());
    vector(const vector& other);
    vector(const vector& other, const Allocator& alloc);
    vector(vector&& other) noexcept;
    vector(vector&& other, const Allocator& alloc) noexcept;
    vector(std::initializer_list<T> init, const Allocator& alloc = Allocator());

    // 析构函数
    ~vector();

    // 大小相关操作
    size_type size() const noexcept;
    size_type max_size() const noexcept;
    void resize(size_type count);
    void resize(size_type count, const value_type& value);
    size_type capacity() const noexcept;
    bool empty() const noexcept;
    void reserve(size_type new_cap);

    // 访问元素
    reference operator[](size_type pos);
    const_reference operator[](size_type pos) const;
    reference at(size_type pos);
    const_reference at(size_type pos) const;
    reference front();
    const_reference front() const;
    reference back();
    const_reference back() const;
    T* data() noexcept;

    // 迭代器操作
    iterator begin() noexcept;
    const_iterator begin() const noexcept;
    const_iterator cbegin() const noexcept;
    iterator end() noexcept;
    const_iterator end() const noexcept;
    const_iterator cend() const noexcept;
    reverse_iterator rbegin() noexcept;
    const_reverse_iterator rbegin() const noexcept;
    const_reverse_iterator crbegin() const noexcept;
    reverse_iterator rend() noexcept;
    const_reverse_iterator rend() const noexcept;
    const_reverse_iterator crend() const noexcept;

    // 修改容器
    void clear() noexcept;
    iterator insert(const_iterator pos, const T& value);
    iterator insert(const_iterator pos, T&& value);
    iterator insert(const_iterator pos, size_type count, const T& value);
    template<typename InputIt>
    iterator insert(const_iterator pos, InputIt first, InputIt last);
    iterator insert(const_iterator pos, std::initializer_list<T> init);
    iterator erase(const_iterator pos);
    iterator erase(const_iterator first, const_iterator last);
    void push_back(const T& value);
    void push_back(T&& value);
    template<typename... Args>
    reference emplace_back(Args&&... args);
    void pop_back();
    void swap(vector& other) noexcept;

    // 分配器相关操作
    allocator_type get_allocator() const noexcept;
};

`std::vector`的源码实现非常复杂，其中包含大量的模板和细节处理。但是，可以看到，它提供了许多方便的方法来访问和修改元素，以及管理容器的大小和内存分配。同时，它还支持迭代器，使得可以在容器中进行遍历和修改。