Vector的一种实现（二）-优快云博客

本文介绍了如何使用C++模板类Vector实现逆置迭代器和swap功能，包括类定义、成员函数实现及测试代码。重点在于提供了一种高效的数据结构实现方式，展示了迭代器的灵活应用。

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增加了逆置迭代器的实现

以及swap功能

完整代码如下：

#ifndef VECTOR_H_
#define VECTOR_H_

#include <stddef.h>
#include <algorithm>
#include <memory>

template <typename T>
class Vector
{
public:
    typedef T *iterator;
    typedef const T *const_iterator;
    typedef size_t size_type;
    typedef T value_type;

    //逆置迭代器
    class reverse_iterator
    {
    public:
        reverse_iterator(iterator it = NULL) :current_(it) { }
        iterator base() const { return current_; }

        reverse_iterator &operator++()
        {
            --current_;
            return *this;
        }
        reverse_iterator operator++(int)
        {
            reverse_iterator temp(*this);
            --current_;
            return temp;
        }
        reverse_iterator &operator--()
        {
            ++current_;
            return *this;
        }
        reverse_iterator operator--(int)
        {
            reverse_iterator temp(*this);
            ++current_;
            return temp;
        }

        T &operator*()
        {
            iterator temp = current_;
            return *--temp;
        }

        T *operator->()
        {
            iterator temp = current_;
            return --temp;
        }

        friend bool operator==(const reverse_iterator &lhs, const reverse_iterator &rhs)
        {
            return lhs.current_ == rhs.current_;
        }

        friend bool operator!=(const reverse_iterator &lhs, const reverse_iterator &rhs)
        {
            return lhs.current_ != rhs.current_;
        }

    private:
        iterator current_;
    };

    //const逆置迭代器
    class const_reverse_iterator
    {
    public:
        const_reverse_iterator(const_iterator it = NULL) :current_(it) { }
        const_iterator base() const { return current_; }

        const_reverse_iterator &operator++()
        {
            --current_;
            return *this;
        }
        const_reverse_iterator operator++(int)
        {
            const_iterator temp(*this);
            --current_;
            return temp;
        }
        const_reverse_iterator &operator--()
        {
            ++current_;
            return *this;
        }
        const_reverse_iterator operator--(int)
        {
            const_iterator temp(*this);
            ++current_;
            return temp;
        }

        const T &operator*() const
        {
            const_iterator temp = current_;
            return *(--temp);
        }

        const T *operator->() const
        {
            const_iterator temp = current_;
            return --temp;
        }

        friend bool operator==(const const_reverse_iterator &lhs, const const_reverse_iterator &rhs)
        {
            return lhs.current_ == rhs.current_;
        }

        friend bool operator!=(const const_reverse_iterator &lhs, const const_reverse_iterator &rhs)
        {
            return lhs.current_ != rhs.current_;
        }

    private:
        const_iterator current_;
    };

    Vector() { create(); }
    explicit Vector(size_type n, const T &t = T())  { create(n, t); }
    Vector(const Vector &v) { create(v.begin(),  v.end()); }
    ~Vector() { uncreate(); }

    Vector &operator=(const Vector &other);
    T &operator[] (size_type i) { return data_[i]; }
    const T &operator[] (size_type i) const { return data_[i]; }

    void push_back(const T &t);
    void swap(Vector &rhs)
    {
        std::swap(data_, rhs.data_);
        std::swap(avail_, rhs.avail_);
        std::swap(limit_, rhs.limit_);
    }

    size_type size() const { return avail_ - data_; }
    size_type capacity() const { return limit_ - data_; }

    iterator begin() { return data_; }
    const_iterator begin() const { return data_; }
    iterator end() { return avail_; }
    const_iterator end() const { return avail_; }


    reverse_iterator rbegin() { return reverse_iterator(end()); }
    const_reverse_iterator rbegin() const { return const_reverse_iterator(end()); }
    reverse_iterator rend() { return reverse_iterator(begin()); }
    const_reverse_iterator rend() const { return const_reverse_iterator(begin()); }
    

private:
    iterator data_; //首元素
    iterator avail_; //末尾元素的下一个位置
    iterator limit_; //内存的后面一个位置

    std::allocator<T> alloc_; //内存分配器

    void create();
    void create(size_type, const T &);
    void create(const_iterator, const_iterator);

    void uncreate();

    void grow();
    void uncheckedAppend(const T &);
};

template <typename T>
Vector<T> &Vector<T>::operator=(const Vector &rhs)
{
    if(this != &rhs)
    {
        uncreate(); //释放原来的内存
        create(rhs.begin(), rhs.end());
    }

    return *this;
}

template <typename T>
void Vector<T>::push_back(const T &t)
{
    if(avail_ == limit_)
    {
        grow();
    }
    uncheckedAppend(t);
}

template <typename T>
void Vector<T>::create()
{
    //分配空的数组
    data_ = avail_ = limit_ = 0;
}

template <typename T>
void Vector<T>::create(size_type n, const T &val)
{
    //分配原始内存
    data_ = alloc_.allocate(n);
    limit_ = avail_ = data_ + n;
    //向原始内存填充元素
    std::uninitialized_fill(data_, limit_, val);
}

template <typename T>
void Vector<T>::create(const_iterator i, const_iterator j)
{
    data_ = alloc_.allocate(j-i);
    limit_ = avail_ = std::uninitialized_copy(i, j, data_);
}

template <typename T>
void Vector<T>::uncreate()
{
    if(data_)
    {
        //逐个进行析构
        iterator it = avail_;
        while(it != data_)
        {
            alloc_.destroy(--it);
        }

        //真正的释放内存
        alloc_.deallocate(data_, limit_ - data_);
    }
    //重置指针
    data_ = limit_ = avail_ = 0;
}

template <typename T>
void Vector<T>::grow()
{
    //内存变为两倍
    size_type new_size = std::max(2 * (limit_ - data_), std::ptrdiff_t(1));
    //分配原始内存
    iterator new_data = alloc_.allocate(new_size);
    //复制元素
    iterator new_avail = std::uninitialized_copy(data_, avail_, new_data);

    uncreate(); //释放以前的内存，以及析构元素

    data_ = new_data;
    avail_ = new_avail;
    limit_ = data_ + new_size;
}

template <typename T>
void Vector<T>::uncheckedAppend(const T &val)
{
    alloc_.construct(avail_++, val);
}


#endif  /* VECTOR_H_ */

测试代码如下：

#include "Vector.hpp"
#include <iostream>
#include <string>
using namespace std;

//测试const reverse迭代器
void print(const Vector<string> &vec)
{
    for(Vector<string>::const_reverse_iterator it = vec.rbegin();
        it != vec.rend();
        ++it)
    {
        cout << *it << " ";
    }
    cout << endl;
}

int main(int argc, char const *argv[])
{
    Vector<string> vec(3, "hello");

    for(Vector<string>::const_iterator it = vec.begin();
        it != vec.end();
        ++it)
    {
        cout << *it << " ";
    }
    cout << endl;

    cout << "size = " << vec.size() << endl;
    cout << "capacity = " << vec.capacity() << endl;
    vec.push_back("foo");
    vec.push_back("bar");

    cout << "size = " << vec.size() << endl;
    cout << "capacity = " << vec.capacity() << endl;

    for(Vector<string>::reverse_iterator it = vec.rbegin();
        it != vec.rend();
        ++it)
    {
        cout << *it << " ";
    }
    cout << endl;


    print(vec);

    Vector<string> vec2;
    vec2.push_back("beijing");
    vec2.push_back("shanghai");
    vec2.push_back("guangzhou");
    print(vec2);

    vec.swap(vec2);
    print(vec);
    print(vec2);

    return 0;
}