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#include<iostream>
#include<string.h>
using namespace std;
class String
{
//Agent pattern of 23 design patterns
class charProxy;
public:
String():_pstr(new char[2])
{
cout<<"String()"<<endl;
initRefcount();
}
String(const char *);
String(const String&);
String& operator=(const String&);
~String()
{
cout<<"~String()"<<endl;
decreaseRefcount();
if(0==useCount())
{
delete []_pstr;
}
}
int useCount()
{
return _pstr[strlen(_pstr)+1];
}
charProxy operator[](int index); //Distinguish between write operations. To return a temporary object here, it cannot be a reference
// char& operator[](int idx)const; //To distinguish read operations, the const keyword must be added, otherwise it will be overloaded with the previous function
private:
char* _pstr;
void initRefcount()
{
_pstr[strlen(_pstr)+1] = 1;
}
void increaseRefcount()
{
++_pstr[strlen(_pstr)+1];
}
void decreaseRefcount()
{
--_pstr[strlen(_pstr)+1];
}
class charProxy
{
public: //These functions must be public
charProxy(String& str,int index):_str(str),_index(index)
{
cout<<"charProxy(String&,int)"<<endl;
}
char& operator=(char ch); //嵌套类里面，也不能返回对象引用;因为嵌套类对象都是临时的
operator char()
{ //类型转换函数，由Charproxy转向char
cout<<"operator char()"<<endl;
return _str._pstr[_index];
}
private:
String& _str;
int _index;
};
friend ostream& operator<<(ostream&,const String&);
friend istream& operator>>(istream&,String&);
};
#if 0
//operator[]()不能区分读操作还是写操作
char & String::operator[](int idx)const //不能区分读写操作，废弃
{
cout<<"operator [](int)const"<<endl;
return _pstr[idx];
}
#endif
String::String(const char* tmp)
{
cout<<"String(const char*)"<<endl;
_pstr = new char[strlen(tmp)+2];
strcpy(_pstr,tmp);
initRefcount(); //引用计数设置为1
}
String::String(const String& lhs)
{
cout<<"String(const String&)"<<endl;
_pstr = lhs._pstr;
increaseRefcount();
}
String& String::operator=(const String& lhs)
{
cout<<"String& operator=(const String&)"<<endl;
decreaseRefcount();
if(0==useCount())
{
delete []_pstr;
}
_pstr = lhs._pstr; // 浅拷贝
increaseRefcount();
return *this;
}
ostream& operator<<(ostream& os,const String& rhs)
{
cout<<"ostream& operator<<(ostream& os,const String&)"<<endl;
os<<rhs._pstr<<endl;
return os;
}
istream& operator>>(istream& is,String& s)
{
cout<<"istream& operator>>(istream&,String&)"<<endl;
is>>s._pstr;
return is;
}
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String::charProxy String::operator[](int index)
{
cout<<"charProxy operator[](int)"<<endl;
return charProxy(*this,index); //return temporary nested class object
}
char& String::charProxy::operator=(char ch)
{
cout<<"char& operator=(char)"<<endl;
if(_index>=0&&_index<strlen(_str._pstr))
{
if(1==_str.useCount()) //When the object has no shared memory
{
_str._pstr[_index] = ch; //modify
return _str._pstr[_index];
}
else
{
_str.decreaseRefcount(); //There is shared memory
char* _strtmp = new char[strlen(_str._pstr)+2];
strcpy(_strtmp,_str._pstr);
_str = _strtmp; // The constructor and assignment constructor are called here, and the destructor is called after the operation
_str[_index] = ch; // Here again mobilize [] overloaded function to modify
_str.initRefcount ();
return _str._pstr[_index];
}
}
}
intmain()
{
String s1("hello,world");
String s2(s1);
cout<<"读操作："<<s1[1]<<endl;
cout<<s1.useCount()<<endl;
cout<<"--------------------------"<<endl;
cout<<"写操作："<<endl;
s1[1] = 'm';
cout<<"--------------------------"<<endl;
cout<<s1[1]<<endl;
cout<<s1.useCount()<<endl;
return 0;
}
//String(const char*)
//String(const String&)
//charProxy operator[](int)
//charProxy(String&,int)
//operator char()
//读操作：e
//2
//--------------------------
//写操作：
//charProxy operator[](int)
//charProxy(String&,int)
//char& operator=(char)
//String(const char*)
//String& operator=(const String&)
//~String()
//charProxy operator[](int)
//charProxy(String&,int)
//char& operator=(char)
//--------------------------
//charProxy operator[](int)
//charProxy(String&,int)
//operator char()
//m
//1
//~String()
//~String()
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| 这里要识别[]操作只能借助嵌套类来底层实现，因为不可能在String类中重写=运算符；所以当遇到[]操作符的时候就转化成CharProxy的对象，必须传引用对其本身操作，在这个类中就可以重写=运算符来区分读和写，因为这里的=我们后面不会再做其他用处只是区分读写；所以这里分三步： 重写[]运算符 先转换为嵌套类对象 重写=，区分s[]和是s[]= 改：  读：  读的时候cout不能输出CharProxy对象，除非重载；采用类型转换比较方便，会根据需要自动转换 |