Deleting an array of pointers to functions?

Question

Here is what I've copied from MSDN about new operator:

The new operator cannot be used to allocate a function, but it can be used to allocate pointers to functions. The following example allocates and then frees an array of seven pointers to functions that return integers.
int (**p) () = new (int (*[7]) ());
delete *p;

Well there is nothing strange with first line, it allocates an array of pointers to functions, but I just don't understand how the second deletes that array? I think it should be:

delete[] *p;

Can anyone explain this?

and how "delete *p;" is valid? that's what I can't figure out — codekiddy
– codekiddy, Commented Nov 17, 2011 at 6:40
@codekiddy, *p in this case is 0 (i.e. NULL), therefore delete *p is a no-op. If you had initialized the first element of the array to point to a function, the behavior of the program would have been undefined (it would have probably crash your program). — avakar
– avakar, Commented Nov 17, 2011 at 6:44
If you quote something, use the quote-formatting and provide a link to the source (I did that for you). — Björn Pollex
– Björn Pollex, Commented Nov 17, 2011 at 8:37

Dmitry Sapelnikov · Accepted Answer · 2011-11-17 08:30:24Z

5

Frankly speaking the right answer was written in the avakar's comment. The right code is

delete[] p;

delete *p; is incorrect for two reasons:

we must use delete[] for all dynamically allocated arrays. Using delete will cause an undefined behaviour.
pointers to static and member functions cannot be deleted

edited Nov 17, 2011 at 8:30

answered Nov 17, 2011 at 8:18

Dmitry Sapelnikov

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3 Comments

Damon Over a year ago

I think your second point is worded unluckily, although you're right that delete *p is wrong on two accounts. Pointers to <whatever> can certainly be deleted, supposed they were allocated. A pointer is, after all, just that, a pointer. However delete *p does not delete the pointer, but tries to delete the pointed-to-function.

Damon Over a year ago

Though admittedly my wording is not much better... since of course not the pointer is deleted, but what's pointed too. So probably "delete takes a pointer and *p isn't a pointer" is the wording that should be correct.

codekiddy Over a year ago

thanks for answer Dmitry, also big thanks to others for answering!

kennytm · Accepted Answer · 2011-11-17 08:44:11Z

2

If we add a typedef,

typedef int (*FPtr)();

the new statement can be rewritten as

FPtr *p = new FPtr[7];

so this is obvious that the resource should be released with

delete[] p;

as explained by others.

BTW, the MSDN page for VS 2008 and above does use the correct code.

int (**p) () = new (int (*[7]) ());
delete [] p;

answered Nov 17, 2011 at 8:44

kennytm

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4 Comments

Björn Pollex Over a year ago

This might be because I added the link by googling, and thus might have linked a different version than the one the OP was quoting. My bad.

kennytm Over a year ago

@codekiddy: It says delete[] in the 2008 US version.

codekiddy Over a year ago

this version doesn't: link

codekiddy Over a year ago

let's try again link

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