explicit call to destructor is not destroying my object why?

Question

I\'m calling the destructor to deallocate memory but it is not deleting my object. What is the reason behind it?

my code is like this:

class A
{
publ         


        

Answer 1

You do not call a destructor like that (well, you can but it's generally not done).

For automatic variables like your b, the destructor will be called at some point when the variable goes out of scope. You don't ever need to call the destructor explicitly.

For objects allocated on the heap with new, the destructor will be called after you delete them. In this case, you also don't call the destructor explicitly.

C++03 states in 12.4 Destructors:

Destructors are invoked implicitly:

• for a constructed object with static storage duration (3.7.1) at program termination;
• for a constructed object with automatic storage duration (3.7.2) when the block in which the object is created exits;
• for a constructed temporary object when the lifetime of the temporary object ends;
• for a constructed object allocated by a new-expression, through use of a delete-expression;
• in several situations due to the handling of exceptions.

Destructors can also be invoked explicitly.

Note: explicit calls of destructors are rarely needed. One use of such calls is for objects placed at specific addresses using a new-expression with the placement option. Such use of explicit placement and destruction of objects can be necessary to cope with dedicated hardware resources and for writing memory management facilities.

You especially don't do what you're trying to do since the destructor will be called twice, once explicitly by you and once implicitly when b goes out of scope. From that same section of the standard:

Once a destructor is invoked for an object, the object no longer exists; the behavior is undefined if the destructor is invoked for an object whose lifetime has ended. Example: if the destructor for an automatic object is explicitly invoked, and the block is subsequently left in a manner that would ordinarily invoke implicit destruction of the object, the behavior is undefined.

This text remains unchanged in the latest draft of C++11 that I have (n3225, November 2010) and it's unlikely it would have changed in essence between that and approval in August 2011.