模拟实现C++中string的常规操作

Posted 2021-08-30 L_add

string中常规操作

• • reserve
  • resize
  • push_back
  • append
  • insert
  • +=
  • []（改）
  • find
  • erase
  • 其他
  • • size()
    • c_str()
    • 其余代码
    • 比较
    • <<
    • >> / getline

reserve

void reserve(size_t n)//开空间，扩展capacity
		{
			if (n > _capacity)
			{
				char* tmp = new char[n + 1];
				strcpy(tmp, _str);
				delete[] _str;
				_str = tmp;
				_capacity = n;
			}
		}

resize

void resize(size_t n,char val = '\\0')//开空间+初始化，扩展capacity,且初始化空间
		{
			//n < size
			if (n < _size)
			{
				_size = n;
				_str[_size] = '\\0';
			}
			else
			{
				//n > capacity
				if (n > _capacity)
				{
					reserve(n);
				}
				// size < n < capacity
				for (size_t i = _size; i < n; i++)
				{
					_str[i] = val;
					
				}
				_str[n] = '\\0';
				_size = n;
			}
			
			
		}

push_back

void push_back(char ch)
		{
			/*if (_size == _capacity)
			{
				reserve(_capacity == 0 ? 4 : _capacity * 2);
			}
			_str[_size] = ch;
			_str[_size + 1] = '\\0';
			_size++;*/
			insert(_size, ch);
		}

append

void append(const char* str)
		{
			/*size_t len = _size + strlen(str);
			if (len > _capacity)
			{
				reserve(len);
			}
			strcpy(_str + _size, str);
			_size = len;*/
			insert(_size, str);
		}

insert

string& insert(size_t pos, char ch)
		{
			assert(pos <= _size);
			if (_size = _capacity)
			{
				reserve(_capacity == 0 ? 4 : _capacity * 2);
			}
			//不推荐
			/*int end = _size;
			while (end > (int)pos)
			{
				_str[end - 1] = _str[end];
				end--;
			}*/
			/*size_t end = _size + 1;
			while (end > pos)
			{
				_str[end] = _str[end - 1];
				end--;
			}*/
			//还可以用指针
			char* end = _str + _size;
			while (end >= _str + pos)
			{
				*(end + 1) = *end;
				end--;
			}
			_str[pos] = ch;
			_size++;
			return *this;
		}
		string& insert(size_t pos, const char *str)
		{
			assert(pos <= _size);
			size_t len = strlen(str);
			if (_size + len > _capacity)
			{
				reserve(_size + len);
			}
			//挪动数据
			char* end = _str + _size;
			while (end >= _str + pos)
			{
				*(end + len) = *end;
				end--;
			}
			strncpy(_str + pos, str, len);
			_size += len;
			return *this;
		}

+=

string& operator += (char ch)
		{
			push_back(ch);
			return *this;
		}
		string& operator += (const char *_str)
		{
			append(_str);
			return *this;
		}

[]（改）

const char& operator[](size_t i) const// 读
		{
			assert(i < _size);

			return _str[i];
		}
		char& operator[](size_t i)//可读可写
		{
			assert(i < _size);
			return _str[i];
		}

find

size_t find(char ch, size_t pos = 0)
		{
			assert(pos < _size);
			for (size_t i = pos; i < _size; i++)
			{
				if (_str[i] == ch)
				{
					return i;
				}
			}
			return npos;
		}
		size_t find(const char* str, size_t pos = 0)
		{
			assert(pos < _size);
			const char* ret = strstr(_str + pos, str);
			if (ret)
			{
				return ret - _str;
			}
			else
			{
				return npos;
			}
		}

erase

string& erase(size_t pos, size_t len = npos)//npos = -1
		{
			assert(pos < _size);
			size_t leftlen = _size - pos;
			//剩余的字符长度小于要删的长度
			if (len >= leftlen)
			{
				_str[pos] = '\\0';
				_size = pos;
			}
			else//剩余的字符长度大于要删的长度
			{
				strcpy(_str + pos, _str + pos + len);
				_size -= len;
			}
			return *this;
		}

其他

size()

size_t size() const 
		{
			return _size;
		}

c_str()

const char* c_str() const
		{
			return _str;
		}

其余代码

class string
	{
	public:
		typedef char* iterator;
		typedef const char* const_iterator;
		iterator begin()
		{
			return _str;
		}
		const_iterator begin() const
		{
			return _str;
		}
		iterator end()
		{
			return _str + _size;
		}
		const_iterator end() const
		{
			return _str + _size;
		}
		string(const char* str = "")
		{
			_size = strlen(str);//_size最后一位留给\\0
			_capacity = _size;
			_str = new char[_capacity + 1];
			strcpy(_str, str);
		}
		void swap(string& s)
		{
			::swap(_str, s._str);
			::swap(_size, s._size);
			::swap(_capacity, s._capacity);
		}
		string(const string& s)
			:_str(nullptr)
			, _size(0)
			, _capacity(0)
		{
			string tmp(s._str);//构造
		/*	swap(_str, tmp._str);
			swap(_size, tmp._size);
			swap(_capacity, tmp._capacity);*/
			//this->swap(tmp)
			swap(tmp);
		}
		string& operator= (string s)
		{
			/*swap(_str, s._str);
			swap(_size, s._size);
			swap(_capacity, s._capacity);*/
			swap(s);
			return *this;
		}
		~string()
		{
			delete[] _str;
			_str = nullptr;
			_size = 0;
			_capacity = 0;
		}

比较

inline bool operator <(const string& s1, const string s2)
	{
		return strcmp(s1.c_str(),s2.c_str()) < 0;
	}
	inline bool operator ==(const string& s1, const string s2)
	{
		return strcmp(s1.c_str(), s2.c_str()) == 0;
	}
	inline bool operator <=(const string& s1, const string s2)
	{
		return s1 < s2 || s1 == s2;
	}
	inline bool operator >(const string& s1, const string s2)
	{
		return !(s1 <= s2);
	}
	
	inline bool operator >=(const string& s1, const string s2)
	{
		return !(s1 < s2);
	}
	
	inline bool operator !=(const string& s1, const string s2)
	{
		return !(s1 == s2);
	}

<<

ostream& operator <<(ostream& out, const string&s)
	{
		for (auto ch : s)
		{
			out << ch;
		}
		return out;
	}

>> / getline

istream& operator >>(istream&in, string& s)
	{
		s.clear();
		char ch;
		ch = in.get();
		while(ch != ' '&& ch != '\\n')
		{
			s += ch;
			ch = in.get();
		}
		return in;
	}
	istream& getline(istream& in, string& s)
	{
		s.clear();
		char ch;
		ch = in.get();
		while ( ch != '\\n')
		{
			s += ch;
			ch = in.get();
		}
		return in;
	}