sizeof type pointed to by pointer?

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

Ole - 07 Dec 2006 10:41 GMT

Hi,

Doing this will work:

double *dPointer;
result = sizeof(*dPointer);

if I want the size (in this case 8) of the type that the pointer is pointing
at, but is there a more correct way to obtain it?

Thanks
Ole

Reply to this Message

William DePalo [MVP VC++] - 07 Dec 2006 15:24 GMT

> Doing this will work:
>
[quoted text clipped - 3 lines]
> if I want the size (in this case 8) of the type that the pointer is
> pointing at, but is there a more correct way to obtain it?

I don't know what "more correct" means in this context.

That said, both

sizeof(double)

and

sizeof(*dpointer)

will yield the same result while

sizeof(dpointer)

yields the size of the pointer itself.

Does that help?

Regards,
Will

Reply to this Message

Tom Widmer [VC++ MVP] - 07 Dec 2006 15:52 GMT

> Hi,
>
[quoted text clipped - 5 lines]
> if I want the size (in this case 8) of the type that the pointer is pointing
> at, but is there a more correct way to obtain it?

Nope, what you've got is fine. sizeof is guaranteed not to evaluate the
expression passed to it, so although your code appears to dereference an
uninitialized pointer, in fact it doesn't.

Tom

Reply to this Message

Ole - 07 Dec 2006 18:17 GMT

>> Hi,
>>
[quoted text clipped - 11 lines]
>
> Tom

Thanks, I was worried about if sizeof would evaluate to a different result
in some special cases like uninitialized pointers etc.

Ole

Reply to this Message

Ben Voigt - 07 Dec 2006 20:25 GMT

>>> Hi,
>>>
[quoted text clipped - 14 lines]
> Thanks, I was worried about if sizeof would evaluate to a different result
> in some special cases like uninitialized pointers etc.

No, sizeof is a purely compile-time operator, with no support for
polymorphism or RTTI. This allows you to use it in place of a literal
constant, for example to declare the size of an array:

union {
double dbl;
char bytes[sizeof(double)];
};

> Ole

Reply to this Message

sizeof type pointed to by pointer?

Free Magazines