class String
{
	friend ostream &operator<<(ostream &os,String &s);
public:
	String(const char *str="");  //全缺省的构造函数，解决空字符串的问题
	String(const String &ps);    //深拷贝
	String &operator=(String s);
	String &operator+=(const char * s);
	const char *C_Str()const    //得到C风格的字符指针
	{
		return _pstr;
	}
	char &operator[](size_t index)
	{
		return _pstr[index];
	}
	size_t Size()const
	{
		return _size;
	}
	void PushBack(char c);
	String &Insert(size_t pos,const char *str);
	//String &operator=(String &s)
	//{
	//	cout<<"String &operator=(String &s)"<<endl;
	//	if(this != &s)
	//	{
	//		delete[]_pstr;
	//		_pstr=new char[strlen(s._pstr)+1];
	//		strcpy(_pstr,s._pstr);
	//	}
	//	return *this;
	//}
	~String()
	{
		cout<<"~String()"<<endl;
		if(_pstr != NULL)
		{
			delete[]_pstr;
		    _pstr=NULL;
		    _size=0;
		    _capacity=0;
		}
	}
private:
	void CheckCapacity(int count);
private:
	int _size;
	int _capacity;
	char *_pstr;
};

ostream &operator<<(ostream &os,String &s)
{
	os<<s._pstr;
	return os;
}

String::String(const char *str)
	:_size(strlen(str))
	,_capacity(strlen(str)+1)
	,_pstr(new char[_capacity])
{
	cout<<"String()"<<endl;
	strcpy(_pstr,str);
}

String::String(const String &ps)
	:_size(ps._size)
	,_capacity(strlen(ps._pstr)+1)
	,_pstr(new char[_capacity])
{
	cout<<"String(const String &ps)"<<endl;
	strcpy(_pstr,ps._pstr);
}

String &String::operator=(String s)
{
	cout<<"String &operator=(String s)"<<endl;
	std::swap(_pstr,s._pstr);
	std::swap(_size,s._size);
	std::swap(_capacity,s._capacity);
	return *this;
}

void String::CheckCapacity(int count)
{
	if(_size+count >= _capacity)
	{
		int _count=(2*_capacity)>(_capacity+count)?(2*_capacity):(_capacity+count);
		char *tmp=new char[_count];
		strcpy(tmp,_pstr);
		delete[]_pstr;
		_pstr=tmp;
		_capacity=_count;
	}
}

void String::PushBack(char c)
{
	CheckCapacity(1);
	_pstr[_size++]=c;
	_pstr[_size]='\0';
}

String &String::operator+=(const char * s)
{

	CheckCapacity(strlen(s));
	while(*s)
	{
		_pstr[_size++]=*s;
		s++;
	}
	_pstr[_size]='\0';
	return *this;
}

String &String::Insert(size_t pos,const char *str)
{
	char *tmp=new char[strlen(_pstr+pos)];
	strcpy(tmp,_pstr+pos);
	CheckCapacity(strlen(str));
	while(*str)
	{
		_pstr[pos++]=*str;
		str++;
	}
	strcpy(_pstr+pos,tmp);
	return *this;
}

void text1()
{
	String str1("hello");
	String str2(str1);
	String str3;
	str3=str1;
	cout<<str1<<endl;
	cout<<str2<<endl;
	cout<<str3<<endl;

	cout<<strlen(str1.C_Str())<<endl;   //5

	str1[4]='w';
	cout<<str1<<endl;   //hellw
}

void text2()
{
	String str1("abcd");
	cout<<str1<<endl;
	str1.PushBack('e');
	str1.PushBack('f');
	str1.PushBack('g');
	str1.PushBack('h');
	str1.PushBack('i');
	cout<<str1<<endl;

	cout<<str1.Size()<<endl;
}

void text3()
{
	String str1("hello");
	String str2("hello world");
	String str3(str2);
	str1+=" ";
	str1+="world";
	cout<<str1<<endl;

	str2.Insert(6," abc ");
	cout<<str2<<endl;
}

//写时拷贝的方式
class String
{
	friend ostream& operator<<(ostream & os,String &s);
public:
	String(const char *str="")
		:_str(new char[strlen(str)+1+4])
	{
		cout<<"构造"<<endl;
		_str+=4;
		*((int *)(_str-4))=1;
		strcpy(_str,str);
	}
	String(String &s)
	{
		cout<<"拷贝构造"<<endl;
		++*((int *)(s._str-4));
		_str=s._str;
	}
	String &operator=(const String &s)
	{
		cout<<"赋值语句"<<endl;
		if(--*(int *)(_str-4) == 0)
		{
			delete[](_str-4);
		}
		++(*(int *)(s._str-4));
		_str=s._str;
		return *this;
	}
	char &operator[](int index)  //写时拷贝
	{
		assert(index >= 0 && index < (int)strlen(_str));
		if(*(int *)(_str-4) > 1)
		{
			--*(int *)(_str-4);
			char *tmp=new char[strlen(_str)+5];
			strcpy(tmp+4,_str);
			delete[](_str-4);
			_str=tmp+4;
			*(int *)(_str-4)=1;
		}
		return _str[index];
	}
	~String()
	{
		cout<<"析构"<<endl;
		if(--*(int *)(_str-4) == 0) 
		{
			cout<<"释放"<<endl;
			delete[](_str-4);
		}
	}
private:
	char *_str;
};
ostream& operator<<(ostream &os,String &s)
{
	os<<s._str;
	return os;
}

void test1()
{
	String str1("abcd");
	cout<<str1<<endl;
	String str2(str1);
	cout<<str2<<endl;
	String str3;
	str3=str1;
	cout<<str3<<endl;
}

void test2()
{
	String str1("abcd");
	cout<<str1<<endl;
	String str2;
	str2=str1;
	cout<<str2<<endl;
	str2[2]='w';
	cout<<str2<<endl;
}