[C++] Difference between delete[] and delete?

0. You shall use delete whenever you allocated with new.
1. You shall use delete[] whenever you allocated with new[].
2. You shall use free() whenever you allocated with malloc().
3. You shall never mix those.
4. You shall never mix those.
5. Goto 3.

[16.12] What if I forget the [] when deleteing array allocated via new T[n]?

At a high level, delete [] pairs with new [], and delete with new.

The technical reason is performance. Consider: delete [] must call a variable number of destructors. This number is stored somewhere (I've heard it is often stored in the memory directly preceding the allocated block). This value is retrieved, the destructors are called in some loop and then the memory is deallocated.

To avoid this overhead of memory and processing with single allocations, we have a separate allocation system for arrays and individuals. In theory, scalar new could be implemented as an array allocation of size one, with delete being the same as delete [].

So this be will a right way to use delete[]?


And this will be a right way to use delete?

Yes, both are correct.

Quote:

Original post by Portishead So this be will a right way to use delete[]? *** Source Snippet Removed *** And this will be a right way to use delete? *** Source Snippet Removed ***

Correct.

There is anyway a third way (but I suggest to first understand "manual" allocation and deallocation), namely using smart pointers, which would let you write code like



My suggestion: Not. Yet. First understand the RAII principle and pointers, and allocation/deallocation. secret hint: the destructors of shared_ptr<> and shared_array<> do the delete and delete[]


edit: Ninja'd by bubu.