class String
{
	public:
		String()
		{
			data = new char[1];  //這里為什么使用new char[1]呢，雖然是一個字符，這是為了和析構(gòu)函數(shù)保持對稱，因為在別的構(gòu)造函數(shù)中使用的char[]
			data[0]='\0';
			length = 0;
		}
		String(const char* str)
		{
			length = strlen(str);
			data = new char[length+1];
			strcpy(data,str);
			data[length]='\0';
		}
		String(const char* str,int n)
		{
			length = n;
			data = new char[n+1];
			strncpy(data,str,n);
			data[length] ='\0';
		}
		String(const String& src) //拷貝構(gòu)造函數(shù) 也就是復(fù)制構(gòu)造函數(shù)
		{
			length = src.length;
			data = new char[length+1];
			strcpy(data,src.data);
		}
		String& operator=(const String& src) //賦值構(gòu)造函數(shù)
		{
			if(this == &src)
				return *this;
			delete [] data;
			data = new char[src.length+1];
			strcpy(data,src.data);
			return *this;
		}
		String& operator=(const char* src) //另一種的賦值構(gòu)造函數(shù)
		{
			delete [] data;
			length = strlen(src);
			data = new char[length+1];
			strcpy(data,src);
			return *this;
		}
		char& operator[](int n)
		{
			return data[n];
		}
		const char& operator[](int n) const  //對于const成員函數(shù) 最好就是返回const的引用，這樣是為了避免返回值被修改
		{
			return data[n];
		}
	friend	ostream& operator<<(ostream& os,const String& st)； 
		 
		~String()
		{
			delete [] data;	
		}
	private:
		char* data;
		int length;	
};
ostream& operator<<(ostream& os,const String& st)
{
   os<<st.data;
  return os;
}