从零开始写STL-string类型

	class string
	{
	public:
		typedef size_t size_type;
		typedef char* iterator;
		typedef char value_type;
	private:
		char *start, *end_of_storage, *End;
		std::allocator<char> data_allocator;
		void DeallocateAndDestory()
		{
			data_allocator.deallocate(start, end_of_storage - start);
		}
		//重新构造元素
		void reallocate(size_t new_size = 0)
		{
			size_t old_size = size();
			if (new_size == 0)
				new_size = size() ? 2 * size() : 1;
			char* new_start = data_allocator.allocate(new_size);
			std::copy(start, start + size(), new_start);
			DeallocateAndDestory();
			start = new_start;
			End = new_start + old_size;
			end_of_storage = new_start + new_size;
		}
		//移动构造元素
		/*void reallocate()
		{
		int old_size = size();
		int new_size = size() ? 2 * size() : 1;
		char* new_start = data_allocator.allocate(new_size);
		char* pos = new_start;
		char* old_pos = start;
		for (int i = 0; i < old_size; i++)
		data_allocator.construct(pos++, std::move(*old_pos)), old_pos++;
		data_allocator.deallocate(start, old_size);
		start = new_start;
		End = new_start + old_size;
		end_of_storage = new_start + new_size;
		}*/
	public:
		//debug
		void print()
		{
			for (auto it = start; it != End; it++)
				std::cout << *it;
			std::cout << std::endl;
		}
		//Construct
		string()
		{
			start = end_of_storage = End = nullptr;
		}
		string(const string& rhs)
		{
			start = end_of_storage = End = nullptr;
			append(rhs);
		}
		string(string&& rhs)noexcept :start(rhs.start), end_of_storage(rhs.end_of_storage), End(rhs.End)
		{
			rhs.start = rhs.end_of_storage = rhs.End = nullptr;
		}
		string(const char* s)
		{
			if (s == nullptr)
				string();
			else
			{
				int cnt = 0;
				for (; s[cnt] != '\0'; cnt++) {}
				start = data_allocator.allocate(cnt);
				std::uninitialized_copy_n(s, cnt, start);
				end_of_storage = End = start + cnt;
			}
		}
		string(size_type n, char c)
		{
			start = data_allocator.allocate(n);
			std::uninitialized_fill_n(start, n, c);
			end_of_storage = End = start + n;
		}
		string(const char* s, size_t n)
		{
			start = data_allocator.allocate(n);
			std::uninitialized_copy_n(s, n, start);
			End = end_of_storage = start + n;
		}
		~string()
		{
			DeallocateAndDestory();
		}
		//Iterator
		const iterator begin() const
		{
			return start;
		}
		const iterator end() const
		{
			return End;
		}
		iterator begin()
		{
			return start;
		}
		iterator end()
		{
			return End;
		}
		//Capacity
		void clear()
		{
			DeallocateAndDestory();
			End = start = end_of_storage = nullptr;
		}
		bool empty()const
		{
			return (start == End);
		}
		const size_type size() const
		{
			return End - start;
		}
		const size_type length() const
		{
			return size();
		}
		const size_type capacity() const
		{
			return end_of_storage - start;
		}
		void resize(size_type n)
		{
			resize(n, value_type());
		}
		void resize(size_type n, const value_type &val)
		{
			if (n <= size())
			{
				End = start + n;
			}
			else
			{
				append(string(n - size(), val));
			}
		}
		void reserve(size_type res_arg = 0)
		{
			if (res_arg + size() < capacity()) return;
			reallocate(res_arg + size());
		}
		//Modifiers
		value_type& operator[](size_type index)
		{
			if (index < 0 || index >= size())
			{
				std::cerr << "index out of range!" << std::endl;
				std::exit(1);
			}
			else
			{
				return *(start + index);
			}
		}
		value_type& front()
		{
			return *start;
		}
		value_type& back()
		{
			auto tmp = end();
			return *(--tmp);
		}
		void push_back(const value_type& val)
		{
			if (size() == capacity())
				reallocate();
			*End = val;
			End++;
		}
		void pop_back()
		{
			if (empty())
			{
				std::cerr << "Error : pop_back() on empty String!" << std::endl;
				exit(1);
			}
			End--;
		}
		void swap(string& rhs)
		{
			std::swap(start, rhs.start);
			std::swap(end_of_storage, rhs.end_of_storage);
			std::swap(End, rhs.End);
		}
		void append(const string& rhs)
		{
			if (rhs.empty()) return;
			if (capacity()<size() + rhs.size()) reallocate(size() + rhs.size());
			std::copy(rhs.start, rhs.end_of_storage, End);
			End += rhs.size();
		}
		void append(const char* s)
		{
			if (s == nullptr) return;
			size_t cnt = 0;
			for (; s[cnt] != '\0'; cnt++) {}
			if (capacity() < size() + cnt)	reallocate(size() + cnt);
			std::uninitialized_copy_n(s, cnt, End);
			End += cnt;
		}
		void append(const char* s, size_t l, size_t r)
		{
			if (r <= l ) return;
			if (s == nullptr) return;
			if (capacity()<size() + r - l - 1) reallocate(size() + r - l);
			std::uninitialized_copy_n(s + l, r - l, End);
			End += r - l;
		}
		string& operator+=(const char c)
		{
			(*this).push_back(c);
			return *this;
		}
		string& operator+=(const string& rhs)
		{
			(*this).append(rhs);
			return *this;
		}
		string operator+(const string& rhs)
		{
			string tmp(*this);
			return tmp += rhs;
		}
		string& operator=(const string& str)
		{
			return assign(str);
		}
		string& operator=(const char* s)
		{
			return assign(string(s));
		}
		string& operator=(char c)
		{
			return assign(string((size_type)1, c));
		}
		string& assign(const string& str)
		{
			clear();
			append(str);
			return (*this);
		}
		string& assign(const char* s)
		{
			clear();
			if (s == nullptr) return *this;
			size_t cnt = 0;
			while (s[cnt] != '\0') cnt++;
			start = data_allocator.allocate(cnt);
			End = std::uninitialized_copy_n(s, cnt, start);
			end_of_storage += cnt;
		}
		string& assign(size_type n, char c)
		{
			clear();
			if (n == 0) return *this;
			start = data_allocator.allocate(n);
			End = end_of_storage = std::uninitialized_fill_n(start, n, c);
		}
		string& insert(size_type pos, const string& rhs)
		{
			pos = std::min(size(), pos);
			size_type new_size = size() + rhs.size();
			iterator new_start = data_allocator.allocate(new_size);
			std::copy(start, start + pos, new_start);
			std::copy(rhs.start, rhs.End, new_start + pos);
			std::copy(start + pos, End, new_start + pos + rhs.size());
			start = new_start;
			end_of_storage = End = new_size + new_start;
			return *this;
		}
		string& insert(size_type pos, const char* s, size_type n)
		{
			return insert(pos, string(s, n));
		}
		string& insert(size_type pos, const char* s)
		{
			return insert(pos, string(s));
		}
		iterator insert(iterator pos, const value_type& val)
		{
			size_type index = pos - start;
			if (size() == capacity())
				reallocate();
			pos = start + index;
			if (pos > end()) pos = end();
			std::copy(pos, End, pos + 1);
			(*pos) = val;
			End++;
			return pos;
		}
		string& insert(size_type pos, size_type num, const value_type& val)
		{
			return insert(pos, string(num, val));
		}
		string& insert(iterator pos, size_type num, const value_type& val)
		{
			return insert(pos - start, string(num, val));
		}
		string& erase(size_type pos, size_type n)
		{
			std::copy(pos + n + start, End, start + pos);
			End = End - n;
			return *this;
		}
		iterator erase(iterator pos)
		{
			std::copy(pos + 1, End, pos);
			End--;
			return pos;
		}
		iterator erase(iterator first, iterator last)
		{
			std::copy(last, End, first);
			End = End - (last - first);
			return first;
		}
		string& replace(size_t pos, size_t n, const string& str)
		{
			erase(pos, n);
			insert(pos, str);
			return *this;
		}
		string& replace(iterator i1, iterator i2, const string& str)
		{
			insert(erase(i1, i2) - start, str);
			return *this;
		}
		const char* c_str() const
		{
			if (empty()) return "";
			char* ret = new char[End - start + 1];
			std::uninitialized_copy(start, End, ret);
			ret[End - start] = '\0';
			return ret;
		}
		bool operator == (const string& rhs)
		{
			if (size() != rhs.size())
				return false;
			else
			{
				for (auto i = start, j = rhs.start; i != End; i++, j++)
				{
					if ((*i) != (*j))
						return false;
				}
				return true;
			}
		}
		bool operator == (const string& rhs) const
		{
			if (size() != rhs.size())
				return false;
			else
			{
				for (auto i = start, j = rhs.start; i != End; i++, j++)
				{
					if ((*i) != (*j))
						return false;
				}
				return true;
			}
		}
		int compare(const string& rhs)
		{
			iterator i = start, j = rhs.start;
			while (i != End && j != rhs.End)
			{
				if ((*i) > (*j))
					return 1;
				else if ((*i) < (*j))
					return -1;
				else
					i++, j++;
			}
			if (i == End&&j == rhs.End)
				return 0;
			else if (i == End)
				return -1;
			else
				return 1;
		}
		size_type copy(char* s, size_type n, size_type pos = 0) const
		{
			if (pos + n >= size())
			{
				std::cerr << "out of range" << std::endl;
				std::exit(1);
			}
			std::uninitialized_copy_n(start + pos, n, s);
			return n;
		}
		size_t find(const string& str, size_t pos = 0) const
		{
			if (size() - pos < str.size())
				return (size_type)(-1);
			for (auto it = start + pos; it != End; it++)
			{
				auto i = it, j = str.start;
				while (j<str.End && *i == *j)
					i++, j++;
				if (j == str.End)
					return it - start;
			}
			return (size_type)(-1);
		}
		size_t find(const char* s, size_t pos, size_t n) const
		{
			return find(string(s, n), pos);
		}
		size_t find(const char* s, size_t pos = 0) const
		{
			return find(string(s), pos);
		}
		size_t find(char c, size_t pos = 0) const
		{
			if (empty())
				return size_type(-1);
			else
			{
				for (auto it = start; it != End; it++)
					if (*it == c)
						return it - start;
				return size_type(-1);
			}
		}
		string substr(size_t pos = 0, size_t n = 0)
		{
			return string(start + pos, n);
		}
		size_t rfind(string& rhs, size_t pos = 0)
		{
			if (pos == 0) pos = size();
			for (auto it = std::min(start + pos, End - 1); it != start - 1; it--)
			{
				size_t i;
				for (i = 0; i < rhs.size();)
					if (rhs[i] == *(it + i))
						i++;
					else
						break;
				if (i == rhs.size())
					return it - start;
			}
			return size_t(-1);
		}
		size_t rfind(const char& c, size_t pos = 0)
		{
			if (pos == 0) pos = size();
			for (auto it = std::min(End - 1, start + pos); it != start; it--)
			{
				if (*it == c)
					return it - start;
			}
			return size_t(-1);
		}
		size_t rfind(const char* str)
		{
			return rfind(string(str));
		}
		size_t find_first_of(const string& rhs, size_t pos = 0)
		{
			for (auto it = start + pos; it != End; it++)
			{
				auto i = rhs.start;
				while (i != rhs.End)
				{
					if (*i == *it)
						break;
					i++;
				}
				if (i != rhs.End)
					return it - start;
			}
			return (size_t)-1;
		}
		size_t find_first_of(const char& c, size_t pos = 0)
		{
			for (auto it = start + pos; it != End; it++)
			{
				if (*it == c)
					return it - start;
			}
			return (size_t)-1;
		}
		size_t find_last_of(const char &c, size_t pos = 0)
		{
			if (pos == 0) pos = size();
			for (auto it = pos + start; it != start - 1; it--)
				if (*it == c)
					return it - start;
			return (size_t)-1;
		}
		size_t find_last_of(const char* str, size_t pos, size_t len)
		{
			size_t l = 0;
			for (size_t i = 0; str[i] != '\0'; i++)
				l++;
			for (auto it = start + pos; it != start + pos - len; it--)
			{
				size_t i;
				for (i = 0; str[i] != '\0'; i++)
					if (str[i] == *it)
						break;
				if (str[i] != '\0') return it - start;
			}
			return size_t(-1);
		}
		size_t find_last_of(const string& rhs, size_t pos)
		{
			for (auto it = start + pos; it != start - 1; it--)
			{
				size_t i = 0;
				while (rhs.start + i != rhs.End)
					if (*it == *(start + i))
						break;
					else
						i++;
				if (rhs.size() != i)	return it - start;
			}
			return size_t(-1);
		}
		size_t find_first_not_of(const string& rhs)
		{
			for (auto it = start; it != End; it++)
			{
				size_t i = 0;
				while (i < rhs.size())
					if (*(rhs.start + i) == *it)
						break;
					else
						i++;
				if (i == rhs.size()) return it - start;
			}
			return size_t(-1);
		}
		size_t find_last_not_of(const string& rhs, size_t pos)
		{
			for (auto it = start + pos; it != start - 1; it--)
			{
				size_t i = 0;
				while (i < rhs.size())
					if (*(rhs.start + i) == *it)
						break;
					else
						i++;
				if (i == rhs.size()) return it - start;
			}
			return size_t(-1);
		}
		bool operator!=(const string& rhs)
		{
			return !(*this == rhs);
		}
		bool operator>(const string& rhs)
		{
			return compare(rhs) > 0;
		}
		bool operator>=(const string& rhs)
		{
			return compare(rhs) >= 0;
		}
		bool operator<(const string& rhs)
		{
			return compare(rhs) < 0;
		}
		bool operator<=(const string& rhs)
		{
			return compare(rhs) <= 0;
		}
	};
	std::ostream& operator<<(std::ostream& os, const ministl::string& rhs)
	{
		os << rhs.c_str();
		return os;
	}
	size_t hash_value(const string& val)
	{
		const size_t _FNV_offset_basis = 2166136261U;
		const size_t _FNV_prime = 16777619U;
		size_t ans = _FNV_offset_basis;
		for (auto it = val.begin(); it != val.end(); it++)
		{
			ans ^= *it;
			ans *= _FNV_prime;
		}
		return ans;
	}
}