删除前删除指针是否会导致内存泄漏？

Question

int *p = new int;

p = NULL;

delete p;

is this a memory leak ??? because the memory location pointed to by pointer p is not freed, its just the pointer that has been NULLed and when we delete, it does not vacate that memory location. Is that so ?

Answer 1

Yes, it does. Yes, it is so. Need more characters!

Answer 2

The reason you will get a memory leak is because p will no longer point to the object that you want to delete.

You typically want to make p NULL after you delete, mostly as a safeguard to double delete, but it is not required. There is no ill effect in delete'ing a NULL pointer, though.

Answer 3

A pointer is just a value pointing to some address of memory - the pointer is not(!) allocated memory! Hence having a new will ask some allocator to reserve some amount of memory and return the address. A delete will ask the same allocator to free that memory. Setting the pointer to zero (before deletion) defeats it and leads to a memory leak.

Answer 4

First of all, deleting a NULL pointer in C++ is actually 'no work done'. It does not give any error too, which sometimes may give you an illusion that the NULL pointer got successfully deleted.

Secondly, since the address to which the pointer p was pointing, let say 1000 (memory address value), had no one else other than this very pointer to identify it, and now that you have changed this only recognizer of 1000 and set it to NULL, the thing which happened is that this 1000 has acquired a memory space but now could not be deleted as "how the hell could I delete something if I don't even know where it is". Hence it is a memory leak.