Multiple delete in destructor

Question

If I have two dynamic arrays as private data members:

std::string* first_array;
std::string* second_array;

I know I can simply delete like this in the destructor

myClass::~myClass()
{
   delete[] first_array;
   delete[] second_array;
}

The concern I have is this, not all the time do I have data inside both array, so is something like this considered best practice ?

myClass::~myClass()
{
   if(first_array)
       delete[] first_array;
   if(second_array)
       delete[] second_array;
}

I tried both and it both worked, not sure which one is better in terms of performance.

1) calling delete on a null pointer value results in a NOP (No-Operation) and is perfectly valid, acceptable, and generally preferred. 2) Use `std::vector` instead. No seriously, **use it**. — Captain Obvlious, Jul 07 '15 at 00:14
Yes, I'm aware of `std::vector`, this is for learning purposes. — hello, Jul 07 '15 at 00:16
possible duplicate of [Is there any reason to check for a NULL pointer before deleting?](http://stackoverflow.com/questions/615355/is-there-any-reason-to-check-for-a-null-pointer-before-deleting) — i_am_jorf, Jul 07 '15 at 00:19

score 6 · Accepted Answer · answered Jul 07 '15 at 00:19

6

The C++ Standard specifies calling delete on a null pointer value will result in a NOP (No-Operation). It is perfectly valid, acceptable, and generally preferred.

answered Jul 07 '15 at 00:19

Captain Obvlious

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score 0 · Answer 2 · answered Jul 07 '15 at 00:44

Deleting a pointer that may be NULL is perfectly ok. As already stated by others, calling delete on a NULL pointer results in a NOP.

However, after deleting any pointer, no matter where, why, how, or when, you should assign the pointer to NULL immediately afterwards. Failing to do this can lead to accidental double-deletion of the pointer, which is catastrophically bad for your program (https://isocpp.org/wiki/faq/freestore-mgmt#double-delete-disaster).

For the same reason that you would not initialize a pointer to some random address, you do not want to leave your pointer dangling in the wind after deleting it, just waiting to be the bullet in your foot.

_"you should assign the pointer to NULL immediately afterwards"_ - Um yeah no. This is pretty pointless to do in a destructor since trying to delete an object twice is already undefined behavior. — Captain Obvlious, Jul 07 '15 at 00:53

Multiple delete in destructor

2 Answers2