string容器简单实现

string字符串在代码编辑中常常出现，本文主要介绍string内部常用函数的实现过程，关键点包含运算符的重载，左值拷贝和右值拷贝，左值运算符重载和右值运算符重载及迭代器的实现过程。相关函数未完全给出，以后会不断更新，敬请期待

#include<iostream>
#include<cstring>
using namespace std;

class String
{
public:
	String(const char* p = nullptr)
	{
		if (p != nullptr)
		{
			_pstr = new char[strlen(p) + 1];
			strcpy(_pstr, p);
		}
		else
		{
			_pstr = new char[1];
			*_pstr = '\0';
		}
	}
	~String()
	{
		delete[]_pstr;
		_pstr = nullptr;
	}
	//带左值引用的拷贝构造
	String(const String& str)
	{
		_pstr = new char[strlen(str._pstr) + 1];
		strcpy(_pstr, str._pstr);
	}
	//带左值引用的赋值运算符重载
	String& operator=(const String& str)
	{
		if (this == &str)
			return *this;
		delete[]_pstr;

		_pstr = new char[strlen(str._pstr) + 1];
		strcpy(_pstr, str._pstr);
		return *this;
	}
	//带右值引用的拷贝构造
	String(String&& str)
	{
		_pstr = str._pstr;
		str._pstr = nullptr;
	}
	//带右值引用的赋值运算符重载
	String& operator=(String&& str)
	{
		if (this == &str)
			return *this;
		delete[]_pstr;

		_pstr = str._pstr;
		str._pstr = nullptr;
		return *this;
	}
	int length() { return strlen(_pstr); }
	const char* c_str() { return _pstr; }
	bool operator==(const String& str) { return strcmp(_pstr, str._pstr) == 0; }
	bool operator!=(const String& str) { return strcmp(_pstr, str._pstr) != 0; }
	char& operator[](int val) { return _pstr[val]; }
	bool operator>(const String& str) { return strcmp(_pstr, str._pstr) > 0; }
	bool operator<(const String& str) { return strcmp(_pstr, str._pstr) < 0; }
	
	friend String operator+(String& str, String& lhs);
	friend ostream& operator<<(ostream& out, const String& str);
private:
	char* _pstr;
	class Iterator
	{
	public:
		Iterator(char* p = nullptr)
			:_p(p) {}
		bool operator!=(const Iterator& it){return _p != it._p;}
		void operator++(){++_p;}
		char& operator*() { return *_p; }
	private:
		char* _p;
	};
public:
	Iterator begin(){return Iterator(_pstr);}
	Iterator end(){return Iterator(_pstr + length());}
	Iterator rbegin() { return Iterator(_pstr + length()); }
	Iterator rend() { return Iterator(_pstr); }
};
ostream& operator<<(ostream& out, const String& str)
{
	out << str._pstr;
	return out;
}
String operator+(String& str, String& lhs)
{
	/*
		这里返回的是值,不是指针或者是引用,原因在于
		局部对象出作用域后会析构,无法找到局部对象的地址
	*/
	String tmp;
	tmp._pstr = new char[str.length() + lhs.length() + 1];
	strcpy(tmp._pstr, str._pstr);
	strcat(tmp._pstr, lhs._pstr);
	return tmp;
}

int main()
{
	String str("abc");
	String str2("def");
	String str3 = str + str2;
	cout << str3 << endl;
	string str4;
	auto it = str3.begin();
	/*
		调用Iterator构造函数,begin返回的_pstr初始化_p
	*/
	for (; it != str3.end(); ++it)
	{
		cout << *it << " ";
	}
	cout << endl;
	cout << (str == str2) << endl;
	return 0;
}