What's the difference between delete-ing a pointer and setting it to nullptr?

Question

Is saying delete pointer and pointer = nullptr the same? Probably not, but does the latter free up memory? What about delete pointer; pointer = nullptr / pointer = nullptr; delete pointer? Why not use that to make a safe way to delete pointers prematurely if required, where they would normally be deleted some other time and cause an error with a normal delete?

Answer 1

It is not the same, because while you may be setting the pointer to null, the contents that the pointer pointed to would still be taking up space.

Doing

delete pointer;
pointer = NULL;

Is fine, but

pointer = NULL;
delete pointer;

Is not, since you already set the pointer to NULL, the delete command will have nothing to delete (or so it thinks). You now have a memory leak because whatever the pointer pointed to beforehand (let's say a linked list) is now floating somewhere in your memory and is untrackable by the program.