cast pointer to different type, what is the impact?

[wenmang]

Hi, all:
I try to understand whether it is a portable to cast a pointer type,
e.g.,
char *ptr = char array[10]; -- a buffer
unsigned char *uptr = ptr;
:
:
function(uptr); -- execute a function that takes unsigned char * as
arg

What is the impact for such cast? is it safe to do this for
memory(buffer) manipulation?
Thanks.

[tom_usenet]

On 7 Jan 2004 06:26:53 -0800, we*****@yahoo.com (wenmang) wrote:

Hi, all:
I try to understand whether it is a portable to cast a pointer type,
It depends on the pointer types.
e.g.,
char *ptr = char array[10]; -- a buffer
unsigned char *uptr = ptr;
Well, obviously you need a cast there (a reinterpret_cast).
function(uptr); -- execute a function that takes unsigned char * as
arg

What is the impact for such cast? is it safe to do this for
memory(buffer) manipulation?

It is generally fine to cast char* to unsigned char* and back again.
Other casts generally aren't fine, but you can reinterpret_cast any
pointer to unsigned char* if you just want to examine or copy the
bytes making up the object pointed to.

Tom

C++ FAQ: http://www.parashift.com/c++-faq-lite/
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html

[Ron Natalie]

"wenmang" <we*****@yahoo.com> wrote in message news:9f**************************@posting.google.c om...

What is the impact for such cast? is it safe to do this for
memory(buffer) manipulation?
Thanks.

You have to reinterpret_cast it, unsigned char* and char* are distinct types.

In this case, it is safe. unsigned char and char (and signed char for that matter)
are required to be compatible.