C++-手把手教你模拟实现string

#pragma once
#include<iostream>
#include<assert.h>
using namespace std;

static size_t npos = -1;
namespace zxf
{
	class string
	{
	public:
		typedef char* iterator;
		typedef const char* const_iterator;
		iterator begin()
		{
			return _str;
		}
		iterator end()
		{
			return _str + _size;
		}
		const_iterator begin()const
		{
			return _str;
		}
		const_iterator end()const
		{
			return _str + _size;
		}
		//string()
		//{
		//	_capacity = 0;
		//	_size = 0;
		//	_str = new char[1];
		//	_str[0] = '\0';
		//}
		string(const char* str="")
		{
			_capacity = strlen(str);
			_size = _capacity;
			_str = new char[_capacity+1];
			strcpy(_str, str); 
		}
		//s2(s1)传统写法
		//string(const string& s)
		//{
		//	_str = new char[s._capacity + 1];
		//	strcpy(_str, s._str);
		//	_size = s._size;
		//	_capacity = s._capacity;
		//}
		//现代写法
		string(const string& s)
		{
			string tmp(s._str);
			swap(tmp);
		}
		~string()
		{
			delete[] _str;
			_str = nullptr;
			_capacity = 0;
			_size = 0;
		}
		const char* c_str() const
		{
			return _str;
		}
		size_t size() const
		{
			return _size;
		}
		size_t capacity() const
		{
			return _capacity;
		}
		void reserve(size_t n)
		{
			char* tmp = new char[n + 1];
			strcpy(tmp, _str);
			delete[]_str;
			_str = tmp;
			_capacity = n;
		}
		void push_back(char ch)
		{
			if (_size == _capacity)
			{
				size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;
				reserve(newcapacity);
			}
			_str[_size] = ch;
			_size++;
			_str[_size] = '\0';
		}
		void append(const char* str)
		{
			size_t len = strlen(str);
			if (_size + len > _capacity)
			{
				reserve(_size + len);
			}
			strcpy(_str + _size, str);
			_size += len;
		}
		void insert(size_t pos,char ch)
		{
			assert(pos >= 0 && pos <= _size);
			if (_size == _capacity)
			{
				size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;
				reserve(newcapacity);
			}
			int end = _size;
			while (end >= (int)pos)
			{
				_str[end+1] = _str[end];
				end--;
			}
			_str[pos] = ch;
			_size++;
		}
		void insert(size_t pos, const char* str)
		{
			assert(pos <= _size);
			size_t len = strlen(str);
			if (_size + len > _capacity)
			{
				reserve(_size + len);
			}
			int end = _size;
			while (end >= (int)pos)
			{
				_str[end + len] = _str[end];
				end--;
			}
			strncpy(_str + pos, str,len);
			_size += len; 
		}
		void erase(size_t pos, size_t len = npos)
		{
			assert(pos < _size);
			if (len == npos || pos + len >= _size)
			{
				_str[pos] = '\0';
				_size = pos;
			}
			else
			{
				strcpy(_str + pos, _str + pos + len);
				_size -= len;
			}
		}
		void swap(string& s)
		{
			std::swap(_str, s._str);
			std::swap(_size, s._size);
			std::swap(_capacity, s._capacity);
		}
		size_t find(char ch,size_t pos = 0)
		{
			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)
		{
			const char* ptr = strstr(_str, str);
			if (ptr == nullptr)
			{
				return npos;
			}
			else
			{
				return ptr - _str;
			}
		}
		void clear()
		{
			_str[0] = '\0';
			_size = 0;
		}
		string substr(size_t pos = 0,size_t len = npos)
		{
			assert(pos < _size);
			size_t end = pos + len;
			if (len == npos || pos + len >= _size)
			{
				end = _size;
			}
			string str;
			str.reserve(end - pos);
			for (size_t i = pos; i < end; i++)
			{
				str += _str[i];
			}
			return str;
		}
		string& operator+=(char ch)
		{
			push_back(ch);
			return *this;
		}
		string& operator+=(const char* str)
		{
			append(str);
			return *this;
		}
		//string& operator=(const string& s)
		//{
		//	if (this != &s)
		//	{
		//		char* tmp = new char[s._capacity + 1];
		//		strcpy(tmp, s._str);
		//		delete[] _str;

		//		_str = tmp;
		//		_size = s._size;
		//		_capacity = s._capacity;
		//	}
		//	return *this;
		//}
		string& operator=(string s)
		{
			swap(s);
			return *this;
		}
		const char& operator[](size_t pos) const
		{
			assert(pos <= _size);
			return _str[pos];
		}
	    char& operator[](size_t pos) 
		{
			assert(pos <= _size);
			return _str[pos];
		}
	private:
		size_t _capacity;
		size_t _size;
		char* _str;
	};

	ostream& operator<<(ostream& out, const string& s)
	{
		for (size_t i = 0; i < s.size(); i++)
		{
			out << s[i];
		}
		return out;
	}
	istream& operator>>(istream& in,string& s)
	{
		char ch;
		in >> ch;
		while (ch != ' ' && ch != '\n')
		{
			s += ch;
			in >>ch;
		}
		return in;
	}
	void Print_string(const string& s)
	{
		for (int i = 0; i < s.size(); i++)
		{
			cout << s[i];
		}
		cout << endl;
	}
	void test_string1()
	{
		string s1("hello world");
		cout<<s1.c_str() << endl;
		string::iterator it = s1.begin();
		while (it != s1.end())
		{
			cout << *it;
			it++;
		}
		cout << endl;
		string::const_iterator cit = s1.begin();
		while (cit != s1.end())
		{
			cout << *cit;
			cit++;
		}
		cout << endl;
	}
	void test_string2()
	{
		string s1("hello world");
		s1 += " ";
		s1 += "zxf";
		string::iterator it = s1.begin();
		while (it != s1.end())
		{
			cout << *it;
			it++;
		}
		cout << endl;
	}
	void test_string3()
	{
		string s1("hello world");
		string s2 = s1;
		cout << s2.c_str() << endl;
		string s3 = s1.substr(2, 4);
		cout << s3.c_str() << endl;
		cout << s3 << endl;
	}
}