C++ memory freeing

mike7411

I am a little confused about when to use delete and delete[]. Is this correct?

int* numArray = new int[100];
delete numArray;

Or should it be this?

int* numArray = new int[100];
delete[] numArray;

I saw the former in an MIT lecture, and it looked suspicious. Both of them compile. Thanks.

Lost User

If you create an array with operator new as above, then you must tell delete that it is an array. So example 2 is the correct way to do it.

Mircea Neacsu

Array delete operator, delete[] invokes the destructor of each array element before freeing the array. For an array of integers, it doesn't make any difference. Meanwhile, if the objects in the array have a non-trivial destructor you should call the delete[] operator.

Mircea

jschell

As noted you should use the correct one. I know for a fact that long ago using the wrong one would cause memory stack corruption. I presume that now that isn't possible or is less likely. Although I would be curious if the spec deals with that specific issue.

k5054

In any case, smart pointers are preferable in almost all cases to new/delete. I imagine that there are some cases where new and delete are preferred to smart pointers, but for most applications, a smart pointer is the better option.

"A little song, a little dance, a little seltzer down your pants" Chuckles the clown

Daniel Pfeffer

Mircea Neacsu wrote:

For an array of integers, it doesn't make any difference.

It is true that no destructor is called for each element of an int[] array, but that does not mean that the memory layout is compatible with delete. For example, the compiler might allocate additional space for a variable containing the size of the array and return a pointer to memory after this variable. When using delete, the heap will be corrupted. The heap layout is implementation-dependent, and therefore you should always match new/delete and new[]/delete[]!

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Mircea Neacsu

While you are absolutely right, I don't know of any heap manager that behaves the way you describe. Let's say that calling delete on an int array is a smaller sin, a "peccadillo" that will place you on one of the first circles of hell. :laugh:

Mircea