How does delete[] "know" the size of the operand array?

The information is not standardised. However in the platforms that I have worked on this information is stored in memory just before the first element. Therefore you could theoretically access it and inspect it, however it's not worth it.

Also this is why you must use delete [] when you allocated memory with new [], as the array version of delete knows that (and where) it needs to look to free the right amount of memory - and call the appropriate number of destructors for the objects.

When you allocate memory on the heap, your allocator will keep track of how much memory you have allocated. This is usually stored in a "head" segment just before the memory that you get allocated. That way when it's time to free the memory, the de-allocator knows exactly how much memory to free.

ONE OF THE approaches for compilers is to allocate a little more memory and to store a count of elements in a head element.

Example how it could be done:

Here

int* i = new int[4];

compiler will allocate sizeof(int)*5 bytes.

int *temp = malloc(sizeof(int)*5)

Will store "4" in the first sizeof(int) bytes

*temp = 4;

and set i

i = temp + 1;

So i will points to an array of 4 elements, not 5.

And deletion

delete[] i;

will be processed in the following way:

int *temp = i - 1;
int numbers_of_element = *temp; // = 4
... call destructor for numbers_of_element elements
... that are stored in temp + 1, temp + 2, ... temp + 4 if needed
free (temp)