Re: Change address of a pointer

From:

Maxim Yegorushkin <maxim.yegorushkin@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sun, 25 Oct 2009 16:00:38 +0000

Message-ID:

<4ae47626$0$9753$6e1ede2f@read.cnntp.org>

On 25/10/09 15:28, Ramon wrote:

How can I change the address of a pointer? Please look at the code
below. What I'm trying to do is to make c = &cell (without using this
notation of course). How can I assign the address of /cell/ (which is
stored in the variable /addr/) to the pointer named /c/??

// creating an object
Cell *cell = new Cell();

// getting the address of the mem location of the object
unsigned int addr = (unsigned int) &cell;

Note that the above line assumes that Cell** pointer can be stored in an
unsigned int. This may work on popular 32-bit architectures, but not on
64-bit ones.

There is an integer type defined in <stdint.h> for this purpose that can
be safely used for storing pointers:

uintptr_t int_addr = reinterpret_cast<uintptr_t>(&cell);

// changing the address of the new pointer to point to the
// 'cell' object
Cell *c = ??? <-- make c point to the address addr

Convert the integer back to Cell** address:

Cell* same_sell = *reinterpret_cast<Cell**>(int_addr); // load
*reinterpret_cast<Cell**>(int_addr) = new Cell; // store

Please note that such code is rather fragile because the compiler won't
check the types for you.

Any reason why you are converting pointers to integers and back?

--
Max