C Array of pointers delete or delete

Question

Cosider the following code   class Foo       Monster  monsters 6        Foo                 for  int i   0  i  lt  6  i                          monsters i    new Monster                         virtual  Foo        What is the correct destructor   this   Foo   Foo         delete    monsters      or this   Foo   Foo         for  int i   0  i  lt  6  i                  delete monsters i             I currently have the uppermost constructor and everything is working okey  but of course I cannot see if it happens to be leaking     Personally  I think the second version is much more logical considering what I am doing  Anyway  what is the  proper  way to do this

User · Answer

For new you should use delete  For new   use delete    Your second variant is correct

User · Answer

delete   monsters   Is incorrect because monsters isn t a pointer to a dynamically allocated array  it is an array of pointers  As a class member it will be destroyed automatically when the class instance is destroyed   Your other implementation is the correct one as the pointers in the array do point to dynamically allocated Monster objects   Note that with your current memory allocation strategy you probably want to declare your own copy constructor and copy-assignment operator so that unintentional copying doesn t cause double deletes   If you you want to prevent copying you could declare them as private and not actually implement them

User · Answer

To simplify the answare let s look on the following code    include  stdafx h   include  lt iostream gt  using namespace std   class A   private      int m id      static int count  public      A    count    m id   count       A int id    m id   id         A    cout lt  lt   Destructor A      lt  lt m id lt  lt endl        int A  count   0   void f1            A  arr   new A 10         delete operate only one constructor  and crash      delete arr        delete   arr     int main         f1        system  PAUSE        return 0      The output is  Destructor A 1  and then it s crashing  Expression   BLOCK TYPE IS VALID phead- nBlockUse     We need to use  delete   arr  becuse it s delete the whole array and not just one cell   try to use delete   arr  the output is  Destructor A 10 Destructor A 9 Destructor A 8 Destructor A 7 Destructor A 6 Destructor A 5 Destructor A 4 Destructor A 3 Destructor A 2 Destructor A 1  The same principle is for an array of pointers   void f2         A   arr   new A  10       for int i   0  i  lt  10  i                  arr i    new A i             for int i   0  i  lt  10  i                  delete arr i    delete the A object allocations             delete   arr   delete the array of pointers     if we ll use delete arr instead of delete   arr  it will not delete the whole pointers in the array    memory leak of pointer objects

User · Answer

delete   monsters is definitely wrong  My heap debugger shows the following output   allocated non-array memory at 0x3e38f0  20 bytes  allocated non-array memory at 0x3e3920  20 bytes  allocated non-array memory at 0x3e3950  20 bytes  allocated non-array memory at 0x3e3980  20 bytes  allocated non-array memory at 0x3e39b0  20 bytes  allocated non-array memory at 0x3e39e0  20 bytes  releasing     array memory at 0x22ff38   As you can see  you are trying to release with the wrong form of delete  non-array vs  array   and the pointer 0x22ff38 has never been returned by a call to new  The second version shows the correct output    allocations omitted for brevity  releasing non-array memory at 0x3e38f0 releasing non-array memory at 0x3e3920 releasing non-array memory at 0x3e3950 releasing non-array memory at 0x3e3980 releasing non-array memory at 0x3e39b0 releasing non-array memory at 0x3e39e0   Anyway  I prefer a design where manually implementing the destructor is not necessary to begin with    include  lt array gt   include  lt memory gt   class Foo       std  array lt std  shared ptr lt Monster gt   6 gt  monsters       Foo                 for  int i   0  i  lt  6    i                        monsters i  reset new Monster                          virtual  Foo                    nothing to do manually

User · Answer

You delete each pointer individually  and then you delete the entire array  Make sure you ve defined a proper destructor for the classes being stored in the array  otherwise you cannot be sure that the objects are cleaned up properly  Be sure that all your destructors are virtual so that they behave properly when used with inheritance

User · Answer

The second one is correct under the circumstances  well  the least wrong  anyway    Edit   least wrong   as in the original code shows no good reason to be using new or delete in the first place  so you should probably just use   std  vector lt Monster gt  monsters    The result will be simpler code and cleaner separation of responsibilities

User · Answer

Your second example is correct  you don t need to delete the monsters array itself  just the individual objects you created

User · Answer

It would make sens if your code was like this    include  lt iostream gt   using namespace std   class Monster   public          Monster     cout  lt  lt   Monster    lt  lt  endl            virtual  Monster     cout  lt  lt   Monster Died   lt  lt  endl        int main int argc  const char  argv              Monster  mon   new Monster 6            delete    mon           return 0

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