C++ ─── string的完整模拟实现

本博客实现了string的常见接口实现

下面是用到的一些函数，供大家回顾复习

改进1：流提取的改进

        原来的代码中流提取中是一个一个字符提取，扩容频率太快，消耗太多

采用buff的方式，buff在栈上，开空间快。

istream& operator>> (istream& is, string& str)
{
	str.clear();
	char buff[128];
	int i = 0;
	char ch = is.get();
	while (ch != ' ' && ch != '\n')
	{
		buff[i++] = ch;
		//0 - 126
		if (i == 127)
		{
			buff[i] = '
';
			str += buff;
			i = 0;
		}
		ch = is.get();
	}
	if (i != 0)
	{
		buff[i] = '
改进二：拷贝构造和赋值重载的改进
';
		str += buff;
	}
	return is;
}

//bit::string s1(s2)  原来的写法
string::string(const string& s)
{
	_str = new char[s._capacity+1];
	strcpy(_str, s._str);
	_size = s._size;
	_capacity = s._capacity;
}
//改进后
//bit::string s2=s1;
string::string(const string& s)
{
	string tmp(s._str);
	std::swap(tmp._str,_str);
	std::swap(tmp._size,_size);
	std::swap(tmp._capacity, _capacity);
}
string::string(const string& s)
{
	string tmp(s._str);
	swap(tmp);
}
注意有些平台s2没有初始化（this指针是随机制），s2与tmp交换后，tmp的_str为随机值，出了函数，tmp会调用析构函数就会崩
解决方案：
在.h文件定义中都加上缺省值
例如：
private:
		//char _buff[16];
		char* _str=nullptr;
		size_t _size = 0;
		size_t _capacity = 0;

​
	//原来的
    string& 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;
	}
//改进后
//s1 = s3
string& string::operator=(const string& s)
{
	if (this != &s)
	{
		string tmp(s._str);
		swap(tmp);
	}
	return *this;
}
string& string::operator=(string tmp)
{
    swap(tmp);
    return *this;
}
​

        传统写法就是1.开空间2.拷贝数据

        使用现代写法（利用构造函数）改进, 利用构造函数，两者实际效率一样但是现代写法更简单快捷

string.h

#define _CRT_SECURE_NO_WARNINGS 1
#pragma once
#include
#include
using namespace std;
namespace bit
{
	class string
	{
	public:
		typedef char* iterator;
		typedef const char* const_iterator;
		iterator begin();
		iterator end();
		const_iterator begin() const;
		const_iterator end() const;
		//string();
		string(const char* str = "");
		string(const string& s);
		string& operator=(const string& s);
		~string();
		const char* c_str() const;
		size_t size() const;
		size_t capacity() const;
		char& operator[](size_t pos);
		const char& operator[](size_t pos) const;
		void reserve(size_t n);
		void push_back(char ch);
		void append(const char* str);
		string& operator+=(char ch);
		string& operator+=(const char* str);
		void insert(size_t pos, char ch);//在pos前面插入
		void insert(size_t pos, const char* str);
		void erase(size_t pos = 0, size_t len = npos);//从pos开始删除
		size_t find(char ch, size_t pos = 0);
		size_t find(const char* str, size_t pos = 0);
		void swap(string& s);
		string substr(size_t pos = 0, size_t len = npos);
		bool operator(const string& s) const;
		bool operator=(const string& s) const;
		bool operator==(const string& s) const;
		bool operator!=(const string& s) const;
		void clear();
	private:
		//char _buff[16];
		char* _str;
		size_t _size;
		size_t _capacity;
		//	  
		//	const static size_t npos = -1;
		//	 ֧
		//	const static double N = 2.2;
		const static size_t npos;
	};
		istream& operator>> (istream& is, string& str);
		ostream& operator _capacity)
		{
			char* tmp = new char[n + 1];
			strcpy(tmp, _str);//复制字符串最后是''
			delete[] _str;
			_str = tmp;
			_capacity = n;
		}
	}
	void string::push_back(char ch)//等价与+=(char ch)
	{
		if (_size == _capacity)
		{
			size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;
			reserve(newcapacity);
		}
		_str[_size++] = ch;
		_str[_size] = '';
	}
	void string::append(const char* str)//等价与+=(const char* ch)
	{
		size_t len = strlen(str);
		if (_size == _capacity)
		{
			size_t newcapacity = _capacity + len;
			reserve(newcapacity);
		}
		//直接从str末尾加入字符串
		strcpy(_str + _size, str);
		_size += len;
	}
	string& string::operator+=(char ch)
	{
		push_back(ch);
		return (*this);
	}
	string& string::operator+=(const char* str)
	{
		append(str);
		return (*this);
	}
	void string::insert(size_t pos, char ch)
	{
		assert(pos  pos)
		{
			_str[end] = _str[end - 1];
			--end;
		}
		_str[end] = ch;
		_size++;
	}
	void string::insert(size_t pos, const char* str)
	{
		size_t len = strlen(str);
		assert(pos  pos)
		{
			_str[end] = _str[end - len];
			--end;
		}
		_size += len;
		//while (len)
		//{
		//	_str[end + len - 1] = str[len-1];
		//	--len;
		//}
		memcpy(_str + pos, str, len);
	}
	void string::erase(size_t pos, size_t len)
	{
		assert(pos  _size - pos)
		{
			_str[pos] = '';
			_size = pos;
		}
		else
		{
			strcpy(_str + pos, _str + pos + len);
			_size -= len;
		}
	}
	size_t string::find(char ch, size_t pos)
	{
		for (size_t i = pos; i  _size - pos)
		{
			string sub(_str + pos);
			return sub;
		}
		else
		{
			string sub;
			sub.reserve(len);
			for (size_t i = 0; i  (istream& is, string& str)
	{
		str.clear();
		char ch = is.get();
		while (ch != ' ' && ch != '\n')
		{
			str += ch;
			ch = is.get();
		}
		return is;
	}
	ostream& operator