Doubt in memcpy() and memset()

[Shhnwz.a]

Hi,
I want to know some of the situations , when to use memcpy() and when
to memset();

Thanx in Advance..

[Kenneth Brody]

Tom St Denis wrote:

>
Kenneth Brody wrote:

No, but if you are passing an int rather than unsigned char, it
may need to zero-fill the rest of the int before passing it.

unsigned char x;
int ix;

x = 4;
ix = x;

What am I missing?

totally legal conversion provided you keep the values in x to the
portable range.

I may be mistaken here, but...

extern void foo(unsigned char c);
extern void bar(int i);

void foobar()
{
unsigned char c = 'x';

foo(c);
bar(c);
}

Here, the call to foo() can push the single byte of c (if the system
allows one to push a byte), or load the byte into a register and then
push the register. However, the call to bar() requires that the byte
be loaded into a register, while zero-filling the register prior to
pushing it on the stack.

Perhaps something like:

load al,[c]
push eax
call foo

xor eax,eax
load al,[c]
push eax
call bar

(Yes, this example assumes the concept of registers and a stack.)

--
+-------------------------+--------------------+-----------------------+
| Kenneth J. Brody | www.hvcomputer.com | #include |
| kenbrody/at\spamcop.net | www.fptech.com | <std_disclaimer .h|
+-------------------------+--------------------+-----------------------+
Don't e-mail me at: <mailto:Th***** ********@gmail. com>

[CBFalconer]

Kenneth Brody wrote:

>

.... snip ...

>
Here, the call to foo() can push the single byte of c (if the system
allows one to push a byte), or load the byte into a register and then
push the register. However, the call to bar() requires that the byte
be loaded into a register, while zero-filling the register prior to
pushing it on the stack.

There is no reason to assume the system has either registers or a
stack. These are not specified in the C standard. In fact, I can
think of systems that dispense with at least one of those concepts
entirely, and handle C perfectly well.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net>

[Kenneth Brody]

CBFalconer wrote:

>
Kenneth Brody wrote:

... snip ...

Here, the call to foo() can push the single byte of c (if the system
allows one to push a byte), or load the byte into a register and then
push the register. However, the call to bar() requires that the byte
be loaded into a register, while zero-filling the register prior to
pushing it on the stack.

There is no reason to assume the system has either registers or a
stack. These are not specified in the C standard. In fact, I can
think of systems that dispense with at least one of those concepts
entirely, and handle C perfectly well.

Yes, I realize that. I was just using register-and-stack-based
system as an example of the difference between passing an int and
an unsigned char to a function, as noted in my last sentence:

(Yes, this example assumes the concept of registers and a stack.)

--
+-------------------------+--------------------+-----------------------+
| Kenneth J. Brody | www.hvcomputer.com | #include |
| kenbrody/at\spamcop.net | www.fptech.com | <std_disclaimer .h|
+-------------------------+--------------------+-----------------------+
Don't e-mail me at: <mailto:Th***** ********@gmail. com>