Deep shallow copy and deep copy. Beginners ' Notes

Both shallow and deep copies are relative copy constructors.

The following code implements a shallow copy,

1#include <stdio.h>2#include <iostream>3#include <string>4 using namespacestd;5 6 classA7 {8     Public :9AintA=0): M_num (a) {};TenAConstA &arr); One        intset_num (); A    Private: -      intM_num; - }; the  -A::a (ConstA &arr) -  { -m_num=Arr.m_num;  +  } - intA::set_num () +  { A     returnM_num; at  } - intMain (void) - { -A arr1 (5); - A arr2 (arr1); -cout <<"arr1="<<arr1.set_num () <<endl<<"arr2="<<arr2.set_num () <<Endl; in return 0; -}

Add one more class member pointer variable,

1#include <stdio.h>2#include <iostream>3#include <string>4 using namespacestd;5 6 classA7 {8     Public :9AintA=0)Ten        { Onecout <<"A"<<Endl; Am_num=A; -M_a=New int[M_num]; -        }; theAConstA &arr); -        intset_num (); -~A (); -    Private: +      intM_num; -      int*m_a; + }; A  atA::a (ConstA &arr) -  { -cout <<"&a"<<Endl; -M_a=arr.m_a; -m_num=Arr.m_num;  -  } in intA::set_num () -  { to     returnM_num; +  } -a::~A () the { *cout <<"~a"<<Endl; $     Delete[]m_a;Panax Notoginseng } - intMain (void) the { +A arr1 (5); A A arr2 (arr1); thecout <<"arr1="<<arr1.set_num () <<endl<<"arr2="<<arr2.set_num () <<Endl; + return 0; -}

The above program copy constructor copies the object's pointer address to the current object's pointer address,

When executing to a destructor, think there are two objects, not to be deleted two times, when running the first time without problems,

When you run the second program, it crashes.

It's going to be a deep copy to solve this problem.

1#include <stdio.h>2#include <iostream>3#include <string>4 using namespacestd;5 6 classA7 {8     Public :9AintA=0)Ten        { Onecout <<"A"<<Endl; Am_num=A; -M_a=New int[M_num]; -        }; theAConstA &arr); -        intset_num (); -        voidset_m_a (); -~A (); +    Private: -      intM_num; +      int*m_a; A }; at  - voida::set_m_a () - { -      for(intI=0; i<m_num;i++) -     { -m_a[i]=i; incout <<"m_a["<<i<<"]="<<m_a[i]<<Endl; -     } to      + } -A::a (ConstA &arr) the  { *m_num=Arr.m_num; $cout <<"&a"<<Endl;Panax NotoginsengM_a=New int[Arr.m_num]; -        for(intI=0; i<arr.m_num;i++) the       { +m_a[i]=Arr.m_a[i]; A       } the        +           -  } $ intA::set_num () $  { -     returnM_num; -  } thea::~A () - {Wuyicout <<"~a"<<Endl; the     Delete[]m_a; - } Wu intMain (void) - { AboutA arr1 (5); $ A arr2 (arr1); -cout <<"arr1="<<arr1.set_num () <<endl<<"arr2="<<arr2.set_num () <<Endl; -cout <<"arr1.m_a="; Arr1.set_m_a (); -cout<<Endl; Acout <<"arr2.m_a="; Arr2.set_m_a (); + return 0; the}

The assignment between this object is not an assignment between the addresses, nor is it freed two times in the same block memory.

Deep shallow copy and deep copy. Beginners ' Notes