【c++】string类---标准库(STL)中的string类

void Teststring()
{
	string s1; // 构造空的string类对象s1
	string s2("hello bit"); // 用C格式字符串构造string类对象s2
	string s3(s2); // 拷贝构造s3
}

union _Bxty
{ // storage for small buffer or pointer to larger one
	value_type _Buf[_BUF_SIZE];
	pointer _Ptr;
	char _Alias[_BUF_SIZE]; // to permit aliasing
} _Bx;

​struct _Rep_base
{
	size_type _M_length;
	size_type _M_capacity;
	_Atomic_word _M_refcount;
};

#pragma once
//#include <iostream>
#include <assert.h>
namespace dc
{
	class string
	{
	public:
		//指针版本
		typedef char* iterator;
		typedef const char* const_iterator;
		const_iterator begin() const
		{
			return _str;
		}
		const_iterator end() const
		{
			return _str + _size;
		}
		iterator begin()
		{
			return _str;
		}
		iterator end()
		{
			return _str + _size;
		}
		//String(char* str = nullptr)
		//	:_size(strlen(str))
		//{
		//	_capacity = _size;
		//	_str = new char[_capacity + 1];
		//	strcpy(_str, str);
		//}
		//String(const char* str = "\0")
		string(const char* str = "")
			:_size(strlen(str))
		{
			_capacity = _size;
			_str = new char[_capacity + 1];
			strcpy(_str, str);
		}
		string& operator=(const string& 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(const string& s)
		{
			_str = new char[s._capacity + 1];
			strcpy(_str, s._str);
			_size = s._size;
			_capacity = s._capacity;
		}
		~string()
		{
			delete[] _str;
			_str = nullptr;
			_size = _capacity = 0;
		}
		const char* c_str() const
		{
			return _str;
		}
		size_t size() const
		{
			return _size;
		}
		size_t capacity() const 
		{
			return _capacity;
		}
		//const对象刻可读不可写
		const char& operator[](size_t pos) const
		{
			assert(pos < _size);
			return _str[pos];
		}
		//普通对象可读可写
		char& operator[](size_t pos)
		{
			assert(pos < _size);
			return _str[pos];
		}
		void resize(size_t n, char ch = '\0')
		{
			if (n <= _size)
			{
				_str[n] = '\0';
				_size = n;
			}
			else
			{
				reserve(n);
				for (size_t i = _size; i < n; i++)
				{
					_str[i] = ch;
				}
				_str[n] = '\0';
				_size = n;
			}
		}
		void reserve(size_t n)
		{
			if (n > _capacity)
			{
				char* tmp = new char[n+1];
				strcpy(tmp, _str);
				delete[] _str;
				_str = tmp;
				_capacity = n;
			}
		}
		void push_back(char ch)
		{
			扩容2倍
			//if (_size == _capacity)
			//{
			//	reserve(_capacity == 0 ? 4 : 2 * _capacity);
			//}
			//_str[_size] = ch;
			//++_size;
			//_str[_size] = '\0';
			insert(_size, ch);
		}
		void append(const char* str)
		{
			扩容
			//size_t len = strlen(str);
			//if (_size + len > _capacity)
			//{
			//	reserve(_size + len);
			//}
			//strcpy(_str + _size, str);
			//_size += len;
			insert(_size, str);
		}
		string& operator+=(char ch)
		{
			push_back(ch);
			return *this;
		}
		string& operator+=(const char* str)
		{
			append(str);
			return *this;
		}
		void insert(size_t pos, char ch)
		{
			assert(pos <= _size);
			//扩容2倍
			if (_size == _capacity)
			{
				reserve(_capacity == 0 ? 4 : 2 * _capacity);
			}
			//size_t end = _size;
			//while (end >= (int)pos)
			//{
			//	_str[end + 1] = _str[end];
			//	--end;
			//}
			//_str[pos] = ch;
			//_size++;
			size_t end = _size+1;
			while (end > pos)
			{
				_str[end] = _str[end-1];
				--end;
			}
			_str[pos] = ch;
			_size++;
		}
		void insert(size_t pos, const char* str)
		{
			assert(pos <= _size);
			//扩容
			size_t len = strlen(str);
			if (_size + len > _capacity)
			{
				reserve(_size + len);
			}
			//string tmp;
			//tmp.reserve(_size + len);
			//tmp += str;
			//tmp += _str;
			//strcpy(_str + pos, tmp.c_str());
			//_size += len;
			size_t end = _size + len;
			while (end > pos + len - 1)
			{
				_str[end] = _str[end - len];
				--end;
			}
			strncpy(_str + pos, str, len);
			_size+=len;
		}
		void erase(size_t pos, size_t len = npos)
		{
			assert(pos < _size);
			if (len == npos || len >= _size - pos)
			{
				_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);
		}
		void swap(string& x, string& y)
		{
		
			x.swap(y);
		}
		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* sub, size_t pos = 0) const
		{
			assert(pos < _size);
			const char* p = strstr(_str + pos, sub);
			if (p)
			{
				return p - _str;
			}
			else
			{
				return npos;
			}
		}
		string substr(size_t pos = 0, size_t len = npos)
		{
			string sub;
			if (len == npos || len >= _size - pos)
			{
				for (size_t i = pos; i < _size; i++)
				{
					sub += _str[i];
				}
			}
			else
			{
				for (size_t i = pos; i < pos + len; i++)
				{
					sub += _str[i];
				}
			}
			return sub;
		}
		void clear()
		{
			_size = 0;
			_str[_size] = '\0';
		}
		//bool operator==(const string& s)
		//{
		//	int ret = strcmp(_str, s._str);
		//	return ret == 0;
		//}
	private:
		char* _str;
		size_t _size;
		size_t _capacity;
	public:
		static const int npos;
	};
	const int string::npos = -1;
	//比较大小
	bool operator==(const string& s1, const string& s2)
	{
		int ret = strcmp(s1.c_str(), s2.c_str());
		return ret == 0;
	}	
	bool operator<(const string& s1, const string& s2)
	{
		int ret = strcmp(s1.c_str(), s2.c_str());
		return ret < 0;
	}
	bool operator<=(const string& s1, const string& s2)
	{
		return s1 < s2 || s1 == s2;
	}
	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);
	}
 
	ostream& operator<<(ostream& out, const string& s)
	{
		for (auto ch : s)
		{
			out << ch;
		}
		return out;
	}
	istream& operator>>(istream& in, string& s)
	{
		s.clear();
		char ch;
		//in >> ch;
		ch = in.get();
		char buff[128];
		size_t i = 0;
		while (ch != ' ' && ch != '\n')
		{
			buff[i++] = ch;
			if (i == 127)
			{
				buff[127] = '\0';
				s += buff;
				i = 0;
			}
			//s += ch;
			//in >> ch;
			ch = in.get();
		}
		if (i > 0)
		{
			buff[i] = '\0';
			s += buff;
		}
		return in;
	}
	istream& getline(istream& in, string& s)
	{
		s.clear();
		char ch;
		//in >> ch;
		ch = in.get();
		while (ch != '\n')
		{
			s += ch;
			//in >> ch;
			ch = in.get();
		}
		return in;
	}
	void test_string()
	{
		string s1;
		string s2("hello world");
		const string s3("111111");
		cout << s1.c_str() << endl;
		cout << s2.c_str() << endl;
		//String s1("hello world");
		//std::string s1("hello world");
		for (size_t i = 0; i < s2.size(); i++)
		{
			cout << s2[i] << " ";
		}
		cout << endl;
		//for (size_t i = 0; i < s2.size(); i++)
		//{
		//	s2[i]++;
		//}
		//cout << endl;
		for (size_t i = 0; i < s3.size(); i++)
		{
			cout << s3[i] << " ";
		}
		cout << endl;
	}
	void test_string2()
	{
		string s1("hello world");
		string::iterator it1 = s1.begin();
		while (it1 != s1.end())
		{
			*it1 -= 3;
			cout << *it1 << " ";
			++it1;
		}
		cout << endl;
		for (auto ch : s1)
		{
			cout << ch << " ";
		}
		cout << endl;
	}
	void test_string3()
	{
		string s1("hello world");
		string::const_iterator it1 = s1.begin();
		while (it1 != s1.end())
		{
			//*it1 -= 3;
			cout << *it1 << " ";
			++it1;
		}
		cout << endl;
		for (auto ch : s1)
		{
			cout << ch << " ";
		}
		cout << endl;
	}
	void test_string4()
	{
		string s1;
		s1.push_back('1');
		s1.push_back('2');
		s1.append("000");
		cout << s1.c_str() << endl;
		//for (auto ch : s1)
		//{
		//	cout << ch << " ";
		//}
		//cout << endl;
		s1 += 'x';
		cout << s1.c_str() << endl;
		s1 += "aaa";
		cout << s1.c_str() << endl;
 
	}
	void test_string5()
	{
		string s1("123456");
		cout << s1.size() << endl;
		//s1.insert(0, '0');
		//s1.insert(s1.size(), '7');
		//cout << s1.c_str() << endl;
		s1.insert(0, "xx");
		cout << s1.size() << endl;
		s1.insert(s1.size(), "888");
		cout << s1.size() << endl;
		cout << s1.capacity() << endl;
		cout << s1.c_str() << endl;
		s1.insert(1, "yy");
		cout << s1.c_str() << endl;
 
	}
	void test_string6()
	{
		string s1("0123456789");
		//s1.erase(0, 1);
		s1.erase(3, 3);
		s1.erase(3);
 
		cout << s1.c_str() << endl;
	}
	void test_string7()
	{
		string s1("hello world");
		string s2(s1);
		string s3;
		s3 = s1;
		s1.resize(20);
		cout << s1.c_str() << endl;
		s1.resize(5);
		cout << s1.c_str() << endl;
		s1.resize(20, 'x');
		cout << s1.c_str() << endl;
		cout << s2.c_str() << endl;
		cout << s3.c_str() << endl;
	}
	void test_string8()
	{
		string s1("hello world");
		string s2("xxxxx xxxxx");
		s1.swap(s2);
		cout << s1.c_str() << endl;
		cout << s2.c_str() << endl;
	}
	void test_string9()
	{
		string s1("hello world");
		cout << s1.find('l', 0) << endl;
		cout << s1.find('l', 5) << endl;
		//char ch[] = "wor";
		//cout << s1.find(ch) << endl;
		cout << s1.find("world",0) << endl;
		cout << s1.substr(5).c_str() << endl;
		cout << s1.substr(5, 2).c_str() << endl;
	}
	void test_string10()
	{
		string s1("123456");
		string s2("123456");
		cout << (s1 == s2) << endl;
		cout << ("123456" == s1) << endl;
		cout << (s1 == "123456") << endl;
	
		cout << s1 << endl;
		cin >> s1 >> s2;
		cout << s1;
		cout << s2;
	}
	void test_string11()
	{
		string s1;
		cout << s1 << endl;
		getline(cin, s1);
		cout << s1 << endl;
		cout << s1.capacity() << endl;
 
 
	}
}

#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
#include <string>
using namespace std;
#include"Class_String_2.h"
//using namespace dc;
int main()
{
	//String s1();
	//String s1("hello word");
	//dc::test_string();
	//dc::test_string2();
	//dc::test_string3();
	//dc::test_string4();
	//dc::test_string5();
	//dc::test_string6();
	//dc::test_string7();
	//cout << typeid(std::string::iterator).name() << endl;
	//cout << typeid(dc::string::iterator).name() << endl;
	//dc::test_string8();
	//dc::test_string9();
	//dc::test_string10();
	dc::test_string11();
 
}

class String
{
public:
	String(const char* str = "")
	{
		// 构造String类对象时，如果传递nullptr指针，可以认为程序非
		if (nullptr == str)
		{
			assert(false);
			return;
		}
		_str = new char[strlen(str) + 1];
		strcpy(_str, str);
	}
	String(const String& s)
		: _str(new char[strlen(s._str) + 1])
	{
		strcpy(_str, s._str);
	}
	String& operator=(const String& s)
	{
		if (this != &s)
		{
			char* pStr = new char[strlen(s._str) + 1];
			strcpy(pStr, s._str);
			delete[] _str;
			_str = pStr;
		}
		return *this;
	}
	~String()
	{
		if (_str)
		{
			delete[] _str;
			_str = nullptr;
		}
	}
private:
	char* _str;
};

class String
{
public:
	String(const char* str = "")
	{
		if (nullptr == str)
		{
			assert(false);
			return;
		}
		_str = new char[strlen(str) + 1];
		strcpy(_str, str);
	}
	String(const String& s)
		: _str(nullptr)
	{
		String strTmp(s._str);
		swap(_str, strTmp._str);
	}
	// 对比下和上面的赋值那个实现比较好？
	String& operator=(String s)
	{
		swap(_str, s._str);
		return *this;
	}
	/*
	String& operator=(const String& s)
	{
	if(this != &s)
	{
	String strTmp(s);
	swap(_str, strTmp._str);
	}return *this;
 }
 */
	~String()
	{
		if (_str)
		{
			delete[] _str;
			_str = nullptr;
		}
	}
private:
	char* _str;
};