【C++】—掌握STL vector类：vector的模拟实现

文章目录

- [💞1. 无参默认构造](#💞1. 无参默认构造)
- [💞2. size](#💞2. size)
- [💞3. capacity](#💞3. capacity)
- [💞4. reserve](#💞4. reserve)
- [💞5. push_back](#💞5. push_back)
- [💞6. operator[]](#💞6. operator[])
- [💞7. 析构函数](#💞7. 析构函数)
- [💞8. 迭代器](#💞8. 迭代器)
- [💞9. empty](#💞9. empty)
- [💞10. pop_back](#💞10. pop_back)
- [💞11. insert](#💞11. insert)
- [💞12.构造函数（initializer_list 版本）](#💞12.构造函数（initializer_list 版本）)
- 💞13.empty
- 💞14.resize
- 💞15.拷贝构造
- 💞16.赋值重载
- 💞17.迭代器区间构造
- 💞18.n个val构造

💞1. 无参默认构造

cpp 复制代码

vector()
	:_start(nullptr)
	, _finish(nullptr)
	, _endofstorage(nullptr)
{}

💞2. size

cpp 复制代码

size_t size() const
{
	return _finish - _start;
}

💞3. capacity

cpp 复制代码

size_t capacity() const
{
	return _endofstorage - _start;
}

💞4. reserve

cpp 复制代码

void reserve(size_t n)
{
	if (n > capacity())
	{
		size_t oldSize = size();
		T* tmp = new T[n];
		if (_start)
		{
			for(size_t i = 0;i < OldSize; i++)
			{
				tmp[i] = _start[i];
			}
			
			delete[] _start;
		}

		_start = tmp;
		_finish = _start + oldSize;
		_endofstorage = _start + n;
	}
}

💞5. push_back

cpp 复制代码

//普通版本
void push_back(const T& x)
{
	if (_finish == _endofstorage)
	{
		reserve(capacity() == 0 ? 4 : capacity() * 2);
	}

	*finish = x;
	++_finish;
}
//insert的复用
void push_back()
{
	insert(_finish,x);
}

💞6. operator[]

cpp 复制代码

//普通版本
T& operator[](size_t i)
{
	assert(i < size());

	return _start[i];
}
//const版本
const T& operator[](size_t i) const
{
	assert(i < size());

	return _start[i];
}

💞7. 析构函数

cpp 复制代码

~vector()
{
	if (_start)
	{
		delete[] _start;
		_start = _finish = _endofstorage = nullptr;
	}
}

💞8. 迭代器

cpp 复制代码

typedef T* iterator;
typedef const T* const_iterator;
//迭代器
iterator begin()
{
	return _start；
}
iterator end()
{
	return _finish;
}
//const迭代器
const_iterator begin() const
{
	return _start；
}
const_iterator end() const
{
	return _finish;
}

💞9. empty

cpp 复制代码

bool empty()
{
	return _start == _finish;
}

💞10. pop_back

cpp 复制代码

void pop_back()
{
	assert(!empty());
	--_finish;
}

💞11. insert

cpp 复制代码

iterator insert(iterator pos, const T& x)
{
	assert(pos >= _start && pos <= _finish);
	if (_finish == _endofstorage)
	{
		size_t len = pos - _start; //不加这句会造成迭代器失效，扩容了pos还指向就空间,就成野指针了
		reserve(capacity() == 0 ? 4 : capacity() * 2);
		pos = _start + len;
	}

	iterator i = _finish - 1;
	while (i >= pos)
	{
		*(i + 1) = *i;
		--i;
	}

	*pos = x;
	++_finish;

	return pos;//返回新插入的位置
}

💞12.构造函数（initializer_list 版本）

cpp 复制代码

vector(initializer_list<T> il)
{
	reserve(il.size());
	for (auto& e : il)
	{
		push_back(e);
	}
}

💞13.empty

cpp 复制代码

iterator erase(iterator pos)
{
	assert(pos >= _start);
	assert(pos < _finish);

	iterator i = pos + 1;
	while (i < _finish)
	{
		*(i - 1) = *i;
		++i;
	}
	--_finish;

	return pos;//返回刚刚被删除位置的下一个位置
}

💞14.resize

cpp 复制代码

void resize(size_t n, T val = T())
{
	if (n < size()) //小于size相当于删除
	{
		_finish = _start + n;
	}
	else
	{
		reserve(n);//先扩容

		while (_finish < _start + n)
		{
			*_finish = val;
			++_finish;
		}
	}
}

💞15.拷贝构造

cpp 复制代码

//拷贝构造
vector(const vector<T>& v)
{
	reserve(v.capacity());
	for (auto& e : v)
	{
		push_back(e);
	}
}

💞16.赋值重载

cpp 复制代码

//交换
void swap(vector<T>& tmp)
{
	std::swap(_start,tmp._start);
	std::swap(_finish,tmp._finish);
	std::swap(_endofstorage,tmp._endofstorage);
}
//赋值重载
//v1 = v3;
vector<T>& operator=(vector<T> v)//传值传参会调用拷贝构造，v3拷贝给v
{
	swap(v); //v和v1交换，函数结束调用析构函数消除v
	return *this;
}

💞17.迭代器区间构造

cpp 复制代码

template<class InputIterator>
vector(InputIterator first, InputIterator last)
{
	while (first != last)
	{
		push_back(*first);
		++first;
	}
}

💞18.n个val构造

cpp 复制代码

vector(int n, const T& val = T())
{
	reserve(n);
	for (size_t i = 0; i < n; i++)
	{
		push_back(val);
	}
}