Does delete on a pointer to a subclass call the base class destructor

Question

I have an class A which uses a heap memory allocation for one of its fields  Class A  is instantiated and stored as a pointer field in another class  class B  When I m done with an object of class B  I call delete  which I assume calls the destructor    But does this call the destructor of class A as well  Edit  From the answers  I take that  please edit if incorrect    delete of an instance of B calls B   B    which calls A   A    A   A should explicitly delete all heap-allocated member variables of the A object  Finally the memory block storing said instance of class B is returned to the heap - when new was used  it first allocated a block of memory on heap  then invoked constructors to initialize it  now after all destructors have been invoked to finalize the object the block where the object resided is returned to the heap

User · Answer

If you have a usual pointer  A   then the destructor will not be called  and memory for A instance will not be freed either  unless you do delete explicitly in B s destructor  If you want automatic destruction look at smart pointers like auto ptr

User · Answer

class B   public      B                p   new int 1024               virtual  B                 cout lt  lt  B destructor  lt  lt endl            p will not be deleted EVER unless you do it manually            int  p       class D   public B   public      virtual  D                 cout lt  lt  D destructor  lt  lt endl             When you do   B  pD   new D    delete pD    The destructor will be called only if your base class has the virtual keyword    Then if you did not have a virtual destructor only  B   would be called   But since you have a virtual destructor  first  D   will be called  then  B     No members of B or D allocated on the heap will be deallocated unless you explicitly delete them    And deleting them will call their destructor as well

User · Answer

The destructor of A will run when its lifetime is over  If you want its memory to be freed and the destructor run  you have to delete it if it was allocated on the heap  If it was allocated on the stack this happens automatically  i e  when it goes out of scope  see RAII    If it is a member of a class  not a pointer  but a full member   then this will happen when the containing object is destroyed   class A       char  someHeapMemory  public      A     someHeapMemory new char 1000           A     delete   someHeapMemory        class B       A  APtr  public      B     APtr new A            B     delete APtr        class C       A Amember  public      C     Amember           C         A is freed   destructed automatically      int main         B  BPtr   new B        delete BPtr     Calls  B   which calls  A        C  CPtr   new C        delete CPtr      B b      C c       b and c are freed destructed automatically   In the above example  every delete and delete   is needed   And no delete is needed  or indeed able to be used  where I did not use it   auto ptr  unique ptr and shared ptr etc    are great for making this lifetime management much easier   class A       shared array lt char gt  someHeapMemory  public      A     someHeapMemory new char 1000           A          someHeapMemory is delete  d automatically     class B       shared ptr lt A gt  APtr  public      B     APtr new A            B           APtr is deleted automatically     int main         shared ptr lt B gt  BPtr   new B         BPtr is deleted automatically

User · Answer

I was wondering why my class  destructor was not called  The reason was that I had forgot to include definition of that class   include  class h    I only had a declaration like  class A   and the compiler was happy with it and let me call  delete

User · Answer

No  the pointer will be deleted  You should call the delete on A explicit in the destructor of B

User · Answer

You have something like  class B      A   a    B   b   new B  b- gt a   new A    If you then call delete b   nothing happens to a  and you have a memory leak   Trying to remember to delete b- gt a  is not a good solution  but there are a couple of others   B   B    delete a     This is a destructor for B that will delete a    If a is 0  that delete does nothing   If a is not 0 but doesn t point to memory from new  you get heap corruption    auto ptr lt A gt  a      b- gt a reset new A     This way you don t have a as a pointer  but rather an auto ptr lt    shared ptr lt   will do as well  or other smart pointers   and it is automatically deleted when b is   Either of these ways works well  and I ve used both

User · Answer

You should delete A yourself in the destructor of B

User · Answer

no it will not call destructor for class A  you should call it explicitly  like PoweRoy told   delete line  delete ptr   in example to compare         include  lt iostream gt     class A          public          A               A            A   A            std  cout  lt  lt   Destructor of A   lt  lt  std  endl         class B          public          B   ptr   new A               B         private          A  ptr          B   B            delete ptr       std  cout  lt  lt   Destructor of B   lt  lt  std  endl         int main            B  b   new B         delete b       return 0

User · Answer

The destructor for the object of class A will only be called if delete is called for that object   Make sure to delete that pointer in the destructor of class B   For a little more information on what happens when delete is called on an object  see  http   www parashift com c  -faq-lite freestore-mgmt html faq-16 9

User · Answer

When you call delete on a pointer allocated by new  the destructor of the object pointed to will be called   A   p   new A   delete p        A  A   called for you on obkect pointed to by p

User · Answer

It is named  destructor   not  deconstructor    Inside the destructor of each class  you have to delete all other member variables that have been allocated with new   edit  To clarify   Say you have  struct A     class B       A  a  public      B      a  new A          B     delete a        class C       A  a  public      C      a  new A                 int main          delete new B      delete new C      Allocating an instance of B and then deleting is clean  because what B allocates internally will also be deleted in the destructor   But instances of class C will leak memory  because it allocates an instance of A which it does not release  in this case C does not even have a destructor

[c++] Does delete on a pointer to a subclass call the base class destructor?

Examples related to c++

Examples related to memory-management

Examples related to destructor

Examples related to delete-operator

Examples related to base-class