Do I have to release heap memory?

[declan]

Let's say I have a pointer like this:

int * meow = new int [25];

Then I create some other array:

int * bloop = new int [30];

Then stuff happens, and I make meow point to the new array:

meow = bloop;

So now meow points to the array of size 30. But what happens to the original stuff it was pointing at? Do I have to manually delete it, or does the heap memory automatically go back to the heap?

Thanks!

[filipe]

You need to delete[] it before you make the pointer point to something else, otherwise it's a memory leak.

[declan]

Ok, that kind of made sense to me, I just thought that c++ might figure out that nothing is holding onto it and let it go. So I want to do:

delete [] meow;

and then

meow = bloop;

? Just to make sure, delete only deletes the heap memory the pointer is pointing at, not the pointer itself, right?

[moorecm]

There are smart pointers that use reference counting and would know better but you have to explicitly use one of them.

Here's a link with more information (see boost::shared_ptr):
http://www.boost.org/doc/libs/1_43_0/libs/smart_ptr/smart_ptr.htm

Actually, if you're using a relatively new compiler it might have the TR1 headers available right out of the box.

[filipe]

Just to make sure, delete only deletes the heap memory the pointer is pointing at, not the pointer itself, right?

Yes. It leaves you with a dangling pointer.

[declan]

Ok, so when memory is leaked, how far does that extend? Let's say I leak lots of memory, but my program finishes execution. Is that memory still leaked, will it slow down my OS? Or will my OS clean it up?

[filipe]

The OS will clean it up. But I suggest not getting into the habit of leaking memory.

[declan]

Alright, thanks!