Thread: Deleting Pointers?

Originally Posted by dwks

Correct.

Just declaring a pointer, and setting it to point at memory allocated for another variable, does not use any memory. In your case, you don't have to free or delete currentNode at all.

Think of it this way. Every new should have one matching delete. Thus, currentNode does not need to be deleted because it was never new'ed.

Ahhhh ok. I get it! Good way of putting it.

Ok, now what happens if I don't do anything with that pointer.

And then back in main, I call delete. Are those pointers within the function still pointing to the object? So it will cause a seg fault?

>> And then back in main, I call delete. Are those pointers within the function still pointing to the object?
If you're back in main, then the function is done. The execution flow of a program follows a specific path. If you call a function and it uses a pointer that points to an object that has been deleted, you will have problems.

There is a concept called ownership of a resource. When you use new to allocate memory, you are creating a resource. Something has to own that resource. Whatever owns that resource is responsible for cleaning it up (in this case by deleting it). Your task as a C++ programmer is to identify which part of the code owns the resource, and make sure that no other code will attempt to use it after the owner has destroyed it.

Of course, in C++, there are many tools available that make managing resources easier. For example, the vector class helps manage a dynamic array. Smart pointers like shared_ptr or auto_ptr help manage raw pointers like the ones you're using. There are container classes like set that do the dirty work and provide most of what you need in a data structure. You should strive to use those tools to make a better problem that doesn't have as many errors when it comes to managing resources. (That doesn't mean it's not a good idea to learn how to do it yourself, though, just don't do it yourself in your real programs if you don't have to.)

Unfortunately, this is a really bad way of solving this issue. You can't rely on the debugger to tell you what to delete and what not to. You have to design and understand the logic of your code to figure out what to delete. Every pointer address returned by new should be deleted once and only once. If you make copies of that address then you need to keep track of the copies and make sure only one is the official copy that gets deleted.

If you have trouble doing this, then you should consider using the tools C++ gives you that manage this for you.