Deep copy problem

When a pointer object is inside a class, there is a crash problem because a shallow copy is pointing to the same piece of memory by two objects! To solve this, a deep copy, write-time copy is introduced.

1. Shallow copy (new open a pointer to do reference counting)

Shallow copy + reference count (pointer) class string{public:string (char* str= "")//default when given \0:_str (new Char[strlen (str) +1]), _pcount (new int (1)) { strcpy (_STR,STR); *_pcount=1;} String (string & S): _str (S._STR), _pcount (S._pcount) {(*_pcount) + +;} string& operator= (const string& s) {if (this!=&s) {this->_release (); _str=s._str;_pcount=s._pcount; (*_ Pcount) + +;} return *this;} ~string () {_release ();} void Print () {printf ("%s%d\n", _str,*_pcount);} protected:char* _str;int* _pcount;void _release () {if (--(*_pcount) ==0) {Delete [] _str;delete _pcount;}}; int main () {String s ("Hello"); S.print (); String S1 (s); S1. Print (); String S2=s;s2. Print (); System ("pause"); return 0;}

2. Shallow copy (leave int data size deposit counter in original string)

Shallow copy + reference count (_str before giving an int data size deposit counter) class string{public:string (char* str= ""): _str (new Char[strlen (str) +5]) {_str+=4; strcpy (_STR,STR); _getcount (_STR) = 1;} String (const string& s)//:_str (new Char[strlen (S._STR) +5])//Copy construction is not a construction, why not open space. Shallow copy points to the same piece of space without opening//: _str (S._STR) {_str+=4;_str=s._str;_getcount (_STR) +=1;} string& operator= (const string& s) {if (this!=&s) {this->_release (); _str+=4;_str=s._str;_getcount (_ STR) +=1;} return *this;} ~string () {_release ();} void Print () {printf ("%s%d\n", _str,_getcount (_STR));} protected:char* _str;int count;void _release () {if (--_getcount (_STR) ==0) {delete [] (_str-4);}} int& _getcount (char* str) {return * ((int*) str-1);}; int main () {String s ("Hello"); S.print (); String S1 (s); S1. Print (); String S2=s;s2. Print (); System ("pause"); return 0;}

3. Deep copy

Deep Copy Class string{public:string (char* str= ""): _str (new Char[strlen (str) +1]) {strcpy (_STR,STR);} String (const string& s)//:_str (new Char[strlen (S._STR) +1])///This method has a wood error: _str (NULL) {//strcpy (_STR,S._STR); String tmp (S._STR); swap (_STR,TMP._STR);} string& operator= (const string& s) {//strcpy (_STR,S._STR); why not. 2 pointers point to the same piece of space. 1) Release 2 times. 2) One move, two changes. 3) _str original memory does not release string tmp (S._STR); swap (_STR,TMP._STR); return *this;} ~string () {delete [] _str;} void Print () {printf ("%s\n", _str);} Protected:char* _str;}; int main () {String s ("Hello"); S.print (); String S1 (s); S1. Print (); String S2=s;s2. Print (); System ("pause"); return 0;}

Use the figure to analyze: 650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M02/7D/F3/wKioL1bzp96QYF5CAAB6iRpf6wo573.png "title = "C++.png" alt= "Wkiol1bzp96qyf5caab6irpf6wo573.png"/>

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Deep copy problem