Simulate and implement common interfaces of string class

One ： understand string Class private

private:
char* _str;
size_t _size;// The effective length of the string 
size_t _capacity;// Space to store the maximum effective length of the string 

Two . Function realization

2.1 Constructors

	// Full default constructor 
		string(const char* s = "")
			:_size(strlen(s))
			,_capacity(strlen(s))
		{
			_str = new char[strlen(s)+1];
			strcpy(_str, s);
		}

2.2 Copy structure

// Implement deep copy problem 
		string(const string& s)
			:_size(strlen(s._str))// Prevent space waste 
			, _capacity(_size)
		{
			_str = new char[_size + 1];
			strcpy(_str, s._str);
		}

2.3 Destructor

~string()
		{
			if (_str)
			{
				delete[] _str;
				_str = nullptr;
				_size = _capacity = 0;
			}
		}

2.4 Return string

The application is c Returns a string in the form of

// Return string 
		const char* c_str()const// This is not const and const Can call 
		{
			return _str;
		}

2.5 Return string length

// Return string length 
		size_t size()const 
		{
			return strlen(_str);
		}

2.6 heavy load =

// heavy load =
		string& operator=(const string s)
		{
			if (this != &s)// Avoid wasting unnecessary time 
			{
				char* tmp = new char[s._capacity + 1];
				strcpy(tmp, s._str);
				_str = tmp;
				_size = s._size;
				_capacity = s._capacity;
			}
			return *this;
		}

2.7 heavy load []

	// heavy load []
		char& operator[](size_t pos)
		{
			assert(pos < strlen(_str));
			return _str[pos];
		}

2.8 Capacity expansion reserve and resize

// Realization reserve

		void reserve(size_t n)
		{
			if (n > _capacity)
			{
				char* tmp = new char[n + 1];
				strcpy(tmp, _str);
				delete[] _str;// Release _str Otherwise, there will be a risk of memory leakage 
				_str = tmp;

				_capacity = n;
			}
		}

// Realization resize
		void resize(size_t n, char ch = '\0')
		{
			if (n < _size)// Shrinkage capacity 
			{
				_size = n;
				_str[n] = '\0';
			}
			else
			{
				if (n > _capacity)
				{
					reserve(n);
				}
				strncpy(_str + _size, _str + n, ch);
				_size = n;
				_str[_size] = '\0';
			}
		}

2.9 Realize the end insertion character （push_back） Or string (append)

// Realization push_back()
		void push_back(char ch)
		{
			// Capacity expansion 
			if (_size == _capacity)
			{
				reserve(_capacity == 0 ? 4 : _capacity * 2);
			}

			_str[_size] = ch;
			++_size;
			_str[_size] = '\0';
		}

// Realization append
		void append(const char* str)
		{
			size_t len = strlen(str);
			// Judge whether to expand capacity 
			if (_size + len > _capacity)
			{
				reserve(_size + len);
			}
			strcpy(_str + _size, str);
			_size += len;
		}

// Realization +=
		string& operator+=(char ch)
		{
			// Reuse 
			push_back(ch);
			return *this;
		}

// Realization +=
		string& operator+=(const char* str)
		{
			append(str);
			return *this;
		}

2.10 Realize random insertion (insert) And random deletion （erase）

// Implement insert 
		string& insert(size_t pos, const char* str)
		{
			// Judge pos Is it legal 
			assert(pos <= _size);
			// Judge whether to expand capacity 
			size_t len = _size + strlen(str);
			if (len > _capacity)
			{
				reserve(len);
			}
			size_t end = _size + strlen(str);
			while (end > pos + strlen(str)-1)
			{
				_str[end] = _str[end-strlen(str)];
				end--;
			}
			strncpy(_str + pos, str, strlen(str));
			_size = len;
			return *this;
		}

Here it is private Define a npos

Initialize outside the class as -1;

const static size_t npos;

string& earse(size_t pos, size_t len = npos)
		{
			assert(pos < _size);
			if (len == npos || pos + len > _size)
			{
				_str[pos] = '\0';
				_size = pos;
			}
			else
			{
				size_t begin = pos + len;
				while (begin <= _size)
				{
					_str[begin - len] = _str[begin];
					begin++;
				}
				_size -= len;
			}
			return *this;
		}

 2.11 Realization find

//1. Find character 
		size_t find(const char ch, size_t pos = 0)
		{
			for (; pos < _size; pos++)
			{
				if (ch == _str[pos])
				{
					return pos;
				}
			}
			return npos;
		}
		//2. Find string 
		size_t find(const char* s, size_t pos = 0)
		{
			char* p = strstr(_str + pos, s);
			if (p != nullptr)
			{
				return p - _str;
			}
			else
				return npos;
		}

2.12 Implement the forward iterator  

ordinary string Use iterator,const The use of embellishments const_iterator

So we should realize overloading

typedef char* iterator;
typedef const char* const_iterator;
//begin
		iterator begin()
		{
			return _str;
		}
		const_iterator begin()const
		{
			return _str;
		}
		//end
		iterator end()
		{
			return _str+_size;
		}
		const_iterator end()const 
		{
			return _str + _size;
		}
		// Heavy load front ++
		iterator operator++()
		{
			return ++_str;
		}

2.13 heavy load << and >>

This can only be done outside the class , Ensure that the left operand is cout

Here, we need to use friend functions to avoid errors .

Friends use ：friend+ Function declaration . Just add this code to the class field .

// heavy load <<
	ostream& operator<<(ostream& out, const string& str)
	{
		for (auto ch : str)// Traverse 
		{
			out << ch;
		}
		return out;
	}
	// heavy load >>
	istream& operator>>(istream& in, string& str)
	{
		char ch;
		ch = in.get();// Read characters in buffer 
		// Avoid multiple expansion 
		char buff[128] = { '\0' };
		size_t i = 0;
		while (ch != ' ' && ch != '\n')
		{
			buff[i++] = ch;
			if (i == 127)
			{
				str += buff;
				i = 0;
				memset(buff, '\0', 128);
			}
			ch = in.get();
		}

		str += buff;
		return in;
	}

2.14 Overload ratio size

It uses C In language strcmp function .

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