Deleting elements of a dynamic array one-by-one

Question

I want to delete a dynamically-allocated array by looping through all the elements and calling delete on each of them.
(I am doing this because I have to "move" an array to another location, that is, to copy the original array and then delete it, but that would take 2x the time than simultaneously copying each element and calling delete on them individually)

I have the following code:

int main()
{
 int *n=new int[2];
 delete n;
 delete (n+1);
} 

But i am getting a Segmentation error each time i run this....

Although, this works fine -:

int main()
{
 int *n=new int[1];
 delete n;
} 

So, my guess is that delete is somehow deleting the whole array instead of a single element!

Could anyone please explain if my guess is right, and if it is, suggest a possible workaround?

I am using GCC 4.7.3 on Ubuntu 13.04

• Manu343726: The most simplest way to do that is using C++ standard containers (std::vector in this case) instead of dynamic arrays, and simply use the erase method of the container. But, on the other hand, what are you trying to do? Why you want to delete elements one-by-one?
• Anmol Singh Jaggi: Actually, I was trying to make another vector-like container of my own. [ Just to gain a better understanding of how std::vectors work under the hood ]
• Manu343726: @Ammol to learn C++? ok. So your question is about the destructor of the vector? This is why you were trying to delete one element by one?
• Anmol Singh Jaggi: Ummm.. kind of! .. As mentioned in the question, I was trying to copy the array to another location and deallocate the original array... [ I was trying to mimic std::vector::resize() operation ]
• Anmol Singh Jaggi: Yeah, I did the same thing earlier. Thanks for the help anyways. :)

Answer 1

You cannot delete the elements individually. When you allocate with new [] you must deallocate with delete []. What you are doing here:

int *n=new int[1];
delete n; // ERROR: should be delete []

it not correct. You are invoking undefined behaviour. It seems to work by pure chance and cannot be relied on.

As for a workaround, it isn't clear what the problem is, but if you want to "move" the array, you could just assign it to a different pointer:

int* n=new int[2];
...
int* m = n;
n = nullptr;
....
delete [] m;

• Anmol Singh Jaggi: Yes, but what was wrong in delete (n+1)? Aren't the individual memory blocks allocated with new only??!
• juanchopanza: @AnmolSinghJaggi It is not allowed by the C++ standard.
• juanchopanza: @AnmolSinghJaggi the point is that new [] allocates a whole array. It doesn't make sense to de-allocate single elements of the array. What could the OS possibly do with them?

Answer 2

To delete

int *n=new int[2];

use

delete [] n;

the code

delete n;

is wrong when you allocate using new [].