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构造函数
vector()
//_begin表示有效成员的开始
//_finish表示有效成员的大小
//_end表示有效的容积
vector():_begin(nullptr),_finish(nullptr),_end(nullptr){}
vector(size_t n, const T& value = T())
//这里不用memcpy拷贝的原因是
//1. memcpy是内存的二进制格式拷贝,将一段内存空间中内容原封不动的拷贝到另外一段内存空间中
//2. 如果拷贝的是内置类型的元素,memcpy既高效又不会出错,但如果拷贝的是自定义类型元素,并且自定义类型元素中涉及到资源管理时,就会出错,因为memcpy的拷贝实际是浅拷贝。
//3.内置类型也有拷贝构造
vector(int n, const T& value = T()):_begin(nullptr), _finish(nullptr), _end(nullptr){_begin = new T[n];_finish = _begin + n;_end = _begin + n;for (int i = 0; i < n; i++){*(_begin + i) = value;}}//便捷写法
/*vector(int n, const T& value = T())
{reserve(n);for (int i = 0; i < n; i++){_begin[i] = value;}
}
vector(int n, const T& value = T())
{resize(n,value);
}*/
vector(InputIterator first, InputIterator last)
//迭代器构造
template<class InputIterator>
vector(InputIterator first, InputIterator last)
{while (first!= last){push_back(*first);//尾插first++; }
}
vector(vector& v)
//拷贝构造
vector(vector<T>& v)
{size_t size = v._finish - v._begin;size_t capacity = v. _end - v._begin;_begin = new T[capacity];for (size_t i = 0; i < size; i++){*(_begin + i) = *(v._begin + i);}_finish = _begin + size;_end = _begin + capacity;
}
//简便写法
vector(vector<T>& v)
{vector<T> tmp(v.begin(),v.end());swap(tmp);
}
析构函数
~vector()
~vector()
{if (_begin){delete[] _begin;_begin = _end = _finish = nullptr;}
}
运算符重载
vector& operator = (vector v)
//赋值拷贝
vector<T>& operator = (vector<T> v)
{swap(v);//这里传的是v的拷贝,改变v并不影响原本的对象return *this;
}
T& operator[](size_t pos);
T& operator[](size_t pos)
{assert(pos >= 0 && pos < size());//pos在有效范围种return _begin[pos];
}
//const对象调用
const T& operator[](size_t pos)const
{assert(pos >= _begin && pos < _finish);return _begin[pos];
}
查询vector容积和大小
size_t size()
size_t capacity()
size_t size() const
{return _finish - _begin;
}size_t capacity() const
{return _end - _begin;
}
size_t size()
{return _finish - _begin;
}size_t capacity()
{return _end - _begin;
}
调整vector的容积和大小
void reserve(size_t n)
void resize(size_t n, const T& value = T())
//这里发生扩容之后,原本的_begin,_finish,_end会发生改变,所以扩容之后要更新
void reserve(size_t n)
{if(n > capacity()){size_t oldsize = size();T* tmp = new T[n];for (size_t i = 0; i < oldsize; i++){tmp[i] = _begin[i];}delete[] _begin;_begin = tmp;_finish = tmp +oldsize;_end = tmp + n;}
}void resize(size_t n, const T& value = T())
{if (n < size()){_finish = _begin + n;}else{if (n > capacity()){reserve(n);}while(_finish < _begin + n){*(_finish++) = value;}}
}
修改vector(头插,尾插,插入,删除,交换)
void push_back(const T& x)
void pop_back()
iterator insert(iterator pos, const T& x)
iterator erase(iterator pos)
void swap(vector& v)
void push_back(const T& x)
{if (_finish == _end){reserve(capacity() == 0? 4: capacity()*2);}*_finish = x;_finish++;}void pop_back()
{assert(_begin != _finish);_finish--;
}
//这里会发生迭代器失效问题、
//原因1:如果发生扩容函数里原pos会变成野指针需要及时更新,函数外pos不会改变,所以要返回pos的新指针
//原因2.因为插入数据,原本pos意义改变,所以要及时更新,让pos指向新插入的元素
//正确做法是返回迭代器插入的指针
iterator insert(iterator pos, const T& x)
{assert(pos >= _begin && pos <= _finish);if (_finish == _end){size_t size = pos - _begin;reserve(capacity() == 0 ? 4 : capacity() * 2);pos = _begin + size;}iterator end = _finish - 1;while (end >= pos){*(end +1) = *(end);end--;}*pos = x;_finish++;return pos;
}
//迭代器失效原因1.erase删除pos位置元素后,pos位置之后的元素会往前搬移,没有导致底层空间的改变,理论上讲迭代器不应该会失效,但是:如果pos刚好是最后一个元素,删完之后pos刚好是end的位置,而end位置是没有元素的,那么pos就失效了。因此删除vector中任意位置上元素时,vs就认为该位置迭代器失效了。
//迭代器失效原因2:erase之后pos位置的意义改变,迭代器所以要更新
//正确做法是返回迭代器下一个的指针
iterator erase(iterator pos)
{assert(pos >= _begin && pos <_finish );iterator end = pos + 1;while (end < _finish){*(end - 1) = *(end);end++;}_finish--;return pos;
}
void swap(vector<T>& v)
{std::swap(_begin,v._begin);std::swap(_finish,v._finish);std::swap(_end,v._end);
}
vector的迭代器
typedef T* iterator;
typedef const T* const_iterator;
完整代码
namespace zjy
{template<class T>class vector{public:typedef T* iterator;typedef const T* const_iterator;iterator begin(){return _begin;}iterator end(){return _finish;}const_iterator cbegin(){return _begin();}const_iterator cend() const{return _finish;}vector():_begin(nullptr),_finish(nullptr),_end(nullptr){}vector(int n, const T& value = T()):_begin(nullptr), _finish(nullptr), _end(nullptr){_begin = new T[n];_finish = _begin + n;_end = _begin + n;for (int i = 0; i < n; i++){*(_begin + i) = value;}}//vector(int n, const T& value = T())//{// reserve(n);// for (int i = 0; i < n; i++)// {// _begin[i] = value;// }//}//vector(int n, const T& value = T())//{// resize(n,value);//}template<class InputIterator>vector(InputIterator first, InputIterator last){while (first!= last){push_back(*first);first++;}}vector(vector<T>& v){size_t size = v._finish - v._begin;size_t capacity = v. _end - v._begin;_begin = new T[capacity];for (size_t i = 0; i < size; i++){*(_begin + i) = *(v._begin + i);}_finish = _begin + size;_end = _begin + capacity;}//vector(vector<T>& v)//{// vector<T> tmp(v.begin(),v.end());// swap(tmp);//}vector<T>& operator = (vector<T> v){swap(v);return *this;}~vector(){if (_begin){delete[] _begin;_begin = _end = _finish = nullptr;}}size_t size() const{return _finish - _begin;}size_t capacity() const{return _end - _begin;}void reserve(size_t n){if(n > capacity()){size_t oldsize = size();T* tmp = new T[n];for (size_t i = 0; i < oldsize; i++){tmp[i] = _begin[i];}delete[] _begin;_begin = tmp;_finish = tmp +oldsize;_end = tmp + n;}}void resize(size_t n, const T& value = T()){if (n < size()){_finish = _begin + n;}else{if (n > capacity()){reserve(n);}while(_finish < _begin + n){*(_finish++) = value;}}}T& operator[](size_t pos){assert(pos >= 0 && pos < size());return _begin[pos];}const T& operator[](size_t pos)const{assert(pos >= _begin && pos < _finish);return _begin[pos];}void push_back(const T& x){if (_finish == _end){reserve(capacity() == 0? 4: capacity()*2);}*_finish = x;_finish++;}void pop_back(){assert(_begin != _finish);_finish--;}void swap(vector<T>& v){std::swap(_begin,v._begin);std::swap(_finish,v._finish);std::swap(_end,v._end);}iterator insert(iterator pos, const T& x){assert(pos >= _begin && pos <= _finish);if (_finish == _end){size_t size = pos - _begin;reserve(capacity() == 0 ? 4 : capacity() * 2);pos = _begin + size;}iterator end = _finish - 1;while (end >= pos){*(end +1) = *(end);end--;}*pos = x;_finish++;return pos;}iterator erase(iterator pos){assert(pos >= _begin && pos <_finish );iterator end = pos + 1;while (end < _finish){*(end - 1) = *(end);end++;}_finish--;return pos;}private:T* _begin = nullptr;T* _finish = nullptr;T* _end = nullptr;};
}