Pointer question [ Newbie ]

[sieg1974]

Hi,

If I declare a pointer to an integer like this

int *intPtr;

what would &intPtr return?

Thanks,

Andre

 

[Joona I Palaste]

Hi,

If I declare a pointer to an integer like this

int *intPtr;

what would &intPtr return?

The address of the variable intPtr itself. This is *NOT* the same thing
as the address of the int that intPtr is pointing to.

--
/-- Joona Palaste ([email protected]) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"When a man talks dirty to a woman, that's sexual harassment. When a woman talks
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- Ruben Stiller

 

[Minti]

Hi,

If I declare a pointer to an integer like this

int *intPtr;

what would &intPtr return?

It's not that hard to figure out if you know what & operator is supposed to
"return". Look in your C manual.

 

[Robert Gamble]

Hi,

If I declare a pointer to an integer like this

int *intPtr;

what would &intPtr return?

&intPtr -- the address of the variable intPtr
intPtr -- the address of an integer (not initialized in your example)
*intPtr -- the value of the integer at the address stored in intPtr

Rob Gamble

 

[Derrick Coetzee]

If I declare a pointer to an integer like this
int *intPtr;
what would &intPtr return?

One useful way to think about this is that the following identity always
holds for any addressable expression e:

*(&e) == e

 

[Dan Pop]

If I declare a pointer to an integer like this

int *intPtr;

what would &intPtr return?

Exactly the same thing as in:

int myint;

where &myint yields the "address" of the variable myint. &intPtr yields
the "address" of the variable intPtr.

Pointers are trickier to the beginner because they have two associated
addresses: the address of the pointed-to object and the address of the
pointer itself. After

intPtr = &myint;

if intPtr is stored at address 0xf00 and myint is stored at address 0xdad
evaluating intPtr will yield 0xdad (represented as a pointer value, not
as an integer value), while &intPtr will yield 0xf00 (again, as a pointer
value).

Making a diagram with pencil and paper might help...

Dan

 

[sieg1974]

Hi,

If I declare a pointer to an integer like this

int *intPtr;

what would &intPtr return?

Thanks,

Andre

And how about ( void ** ) &intPtr ?

 

[Barry Schwarz]

And how about ( void ** ) &intPtr ?

Implementation dependent

If a void** can properly hold the value of an int**, then it will
return the same value as &intPtr but coerced into the form of a
void**.

If it cannot, then you have invoked undefined behavior.


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[Dan Pop]

What's the point of such a conversion? What *exactly* do you expect from
it? The type void ** has none of the nice properties of the type void *
and &intPtr can be safely converted to void *.

Implementation dependent

If a void** can properly hold the value of an int**, then it will
return the same value as &intPtr but coerced into the form of a
void**.

If it cannot, then you have invoked undefined behavior.

AFAICT, undefined behaviour can occur only if the int** value is not
properly aligned for a void**.

Dan

 

[Barry Schwarz]

What's the point of such a conversion? What *exactly* do you expect from
it? The type void ** has none of the nice properties of the type void *
and &intPtr can be safely converted to void *.


AFAICT, undefined behaviour can occur only if the int** value is not
properly aligned for a void**.

What if sizeof(void**) < sizeof(int**)?


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