Clearing an array

[Terry Andersen]

I have an array that I initialize to zero, like:

Buffer[300] = {0x00};

How do I in my code reset this array to all zeros ones more? Without running
a whole for loop?

Best Regards
Terry

[Robert Stankowic]

Re: Clearing an array


"Terry Andersen" <terr@sea.com > schrieb im Newsbeitrag
news:bk4eck$4dn $1@news.net.uni-c.dk...[color=blue]
> I have an array that I initialize to zero, like:
>
> Buffer[300] = {0x00};
>
> How do I in my code reset this array to all zeros ones more? Without[/color]
running[color=blue]
> a whole for loop?
>[/color]

memset(Buffer, 0x00, sizeof Buffer);

Robert

[pete]

Re: Clearing an array

Terry Andersen wrote:[color=blue]
>
> I have an array that I initialize to zero, like:
>
> Buffer[300] = {0x00};
>
> How do I in my code reset this array to all zeros ones more?
> Without running a whole for loop?[/color]

A loop might be best.
There's no single operation that will do it.

[pete]

Re: Clearing an array

Robert Stankowic wrote:[color=blue]
>
> "Terry Andersen" <terr@sea.com > schrieb im Newsbeitrag
> news:bk4eck$4dn $1@news.net.uni-c.dk...[color=green]
> > I have an array that I initialize to zero, like:
> >
> > Buffer[300] = {0x00};
> >
> > How do I in my code reset this array to all zeros ones more?[/color]
> Without running a whole for loop?[color=green]
> >[/color]
>
> memset(Buffer, 0x00, sizeof Buffer);[/color]

Not knowing the representation of ((*Buffer)0),
memset() might or might not work right.

[Lew Pitcher]

Re: Clearing an array

On Mon, 15 Sep 2003 15:26:35 +0200, "Terry Andersen" <terr@sea.com > wrote:
[color=blue]
>I have an array that I initialize to zero, like:
>
>Buffer[300] = {0x00};
>
>How do I in my code reset this array to all zeros ones more? Without running
>a whole for loop?[/color]

#include <string.h>

memset(Buffer, 0, sizeof Buffer);
[color=blue]
>Best Regards
>Terry
>
>[/color]

--
Lew Pitcher
IT Consultant, Enterprise Technology Solutions
Toronto Dominion Bank Financial Group

(Opinions expressed are my own, not my employers')

[Ed Morton]

Re: Clearing an array



Terry Andersen wrote:
[color=blue]
> I have an array that I initialize to zero, like:
>
> Buffer[300] = {0x00};
>
> How do I in my code reset this array to all zeros ones more? Without running
> a whole for loop?
>
> Best Regards
> Terry[/color]

If you can put it inside a structure, you could create a zero-filled
instance and assign your buffer to that, e.g. this:

#include<stdio. h>
#include<string .h>

#define BUFFSIZE 9

typedef struct {
int Buffer[BUFFSIZE];
} BUFFSTRUCT;

static const BUFFSTRUCT ZeroBuffStruct;

void prtBuf(int buf[])
{
int i;
for (i=0; i<BUFFSIZE; i++)
printf("%d",buf[i]);
printf("\n");
}

int main()
{
BUFFSTRUCT BufStruct;
int *Buffer = BufStruct.Buffe r;

BufStruct = ZeroBuffStruct;
prtBuf(Buffer);

Buffer[3] = 4;
prtBuf(Buffer);

BufStruct = ZeroBuffStruct;
prtBuf(Buffer);

return 1;
}

produces the output:

Buffer="0000000 0"
Buffer="0004000 0"
Buffer="0000000 0"

If that's non-portable or has other problems, I'm sure someone will let
us know....

Regards,

Ed.

[Thomas Pfaff]

Re: Clearing an array

Lew.Pitcher@td. com (Lew Pitcher) writes:
[color=blue]
> On Mon, 15 Sep 2003 15:26:35 +0200, "Terry Andersen" <terr@sea.com > wrote:
>[color=green]
> >I have an array that I initialize to zero, like:
> >
> >Buffer[300] = {0x00};
> >
> >How do I in my code reset this array to all zeros ones more? Without running
> >a whole for loop?[/color]
>
> #include <string.h>
>
> memset(Buffer, 0, sizeof Buffer);
>[/color]

That's not guaranteed to work unless `Buffer' is of type unsigned char, is it?

[Robert Stankowic]

Re: Clearing an array


"pete" <pfiland@mindsp ring.com> schrieb im Newsbeitrag
news:3F65C3AD.6 A6@mindspring.c om...[color=blue]
> Robert Stankowic wrote:[color=green]
> >
> > "Terry Andersen" <terr@sea.com > schrieb im Newsbeitrag
> > news:bk4eck$4dn $1@news.net.uni-c.dk...[color=darkred]
> > > I have an array that I initialize to zero, like:
> > >
> > > Buffer[300] = {0x00};
> > >
> > > How do I in my code reset this array to all zeros ones more?[/color]
> > Without running a whole for loop?[color=darkred]
> > >[/color]
> >
> > memset(Buffer, 0x00, sizeof Buffer);[/color]
>
> Not knowing the representation of ((*Buffer)0),
> memset() might or might not work right.[/color]

You are ritght, of course. Somehow the 0x00 made me think of unsigned char.
Shame on me.
Robert

[Thomas Matthews]

Re: Clearing an array

Thomas Pfaff wrote:
[color=blue]
> Lew.Pitcher@td. com (Lew Pitcher) writes:
>
>[color=green]
>>On Mon, 15 Sep 2003 15:26:35 +0200, "Terry Andersen" <terr@sea.com > wrote:
>>
>>[color=darkred]
>>>I have an array that I initialize to zero, like:
>>>
>>>Buffer[300] = {0x00};
>>>
>>>How do I in my code reset this array to all zeros ones more? Without running
>>>a whole for loop?[/color]
>>
>> #include <string.h>
>>
>> memset(Buffer, 0, sizeof Buffer);
>>[/color]
>
>
> That's not guaranteed to work unless `Buffer' is of type unsigned char, is it?[/color]

It will work on any platform where the data type of buffer can be set
to zero in all bytes. If the platform has a data type where the value
of zero is not zeros in all bytes, then it won't work.

--
Thomas Matthews

C++ newsgroup welcome message:

http://www.slack.net/~shiva/welcome.txt

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alt.comp.lang.l earn.c-c++ faq:

http://www.raos.demon.uk/acllc-c++/faq.html

Other sites:
http://www.josuttis.com -- C++ STL Library book

[Christopher Benson-Manica]

Re: Clearing an array

pete <pfiland@mindsp ring.com> spoke thus:
[color=blue]
> Not knowing the representation of ((*Buffer)0),
> memset() might or might not work right.[/color]

Why is this so? Are you saying that if Buffer were

long Buffer[300];

that memset wouldn't work, even if you did

memset( Buffer, 0, 300 * sizeof(long) );

?

--
Christopher Benson-Manica | Jumonji giri, for honour.
ataru(at)cybers pace.org |

[Thomas Pfaff]

Re: Clearing an array

Christopher Benson-Manica <ataru@nospam.c yberspace.org> writes:
[color=blue]
> pete <pfiland@mindsp ring.com> spoke thus:
>[color=green]
> > Not knowing the representation of ((*Buffer)0),
> > memset() might or might not work right.[/color]
>
> Why is this so? Are you saying that if Buffer were
>
> long Buffer[300];
>
> that memset wouldn't work, even if you did
>
> memset( Buffer, 0, 300 * sizeof(long) );[/color]

See `Defect Report #263':

http://wwwold.dkuug.dk/JTC1/SC22/WG14/www/docs/dr_263.htm

[Lew Pitcher]

Re: Clearing an array

On 15 Sep 2003 17:13:24 +0200, Thomas Pfaff <thomas.pfaff@t iscali.no> wrote:
[color=blue]
>Lew.Pitcher@td .com (Lew Pitcher) writes:
>[color=green]
>> On Mon, 15 Sep 2003 15:26:35 +0200, "Terry Andersen" <terr@sea.com > wrote:
>>[color=darkred]
>> >I have an array that I initialize to zero, like:
>> >
>> >Buffer[300] = {0x00};
>> >
>> >How do I in my code reset this array to all zeros ones more? Without running
>> >a whole for loop?[/color]
>>
>> #include <string.h>
>>
>> memset(Buffer, 0, sizeof Buffer);
>>[/color]
>
>That's not guaranteed to work unless `Buffer' is of type unsigned char, is it?[/color]

You are correct, of course.

--
Lew Pitcher
IT Consultant, Enterprise Technology Solutions
Toronto Dominion Bank Financial Group

(Opinions expressed are my own, not my employers')

[Joe Wright]

Re: Clearing an array

Ed Morton wrote:[color=blue]
>
> Terry Andersen wrote:
>[color=green]
> > I have an array that I initialize to zero, like:
> >
> > Buffer[300] = {0x00};
> >
> > How do I in my code reset this array to all zeros ones more? Without running
> > a whole for loop?
> >
> > Best Regards
> > Terry[/color]
>
> If you can put it inside a structure, you could create a zero-filled
> instance and assign your buffer to that, e.g. this:
>
> #include<stdio. h>
> #include<string .h>
>
> #define BUFFSIZE 9
>
> typedef struct {
> int Buffer[BUFFSIZE];
> } BUFFSTRUCT;
>
> static const BUFFSTRUCT ZeroBuffStruct;
>
> void prtBuf(int buf[])
> {
> int i;
> for (i=0; i<BUFFSIZE; i++)
> printf("%d",buf[i]);
> printf("\n");
> }
>
> int main()
> {
> BUFFSTRUCT BufStruct;
> int *Buffer = BufStruct.Buffe r;
>
> BufStruct = ZeroBuffStruct;
> prtBuf(Buffer);
>
> Buffer[3] = 4;
> prtBuf(Buffer);
>
> BufStruct = ZeroBuffStruct;
> prtBuf(Buffer);
>
> return 1;
> }
>
> produces the output:
>
> Buffer="0000000 0"
> Buffer="0004000 0"
> Buffer="0000000 0"
>
> If that's non-portable or has other problems, I'm sure someone will let
> us know....
>
> Regards,
>
> Ed.[/color]

You're crazy! I love the way your mind works. Really! How about this..

#include <stdio.h>

#define SA 10

typedef struct arr {
int arr[SA];
} arr;

arr st_arr;


int main(void) {
int array[SA] = { 0 }; /* initialize array */
printf("%5d\n", array[0]); /* show that array[0] == 0 */
array[0] = SA; /* change it to something else */
printf("%5d\n", array[0]); /* show the change */
printf("%5d\n", st_arr.arr[0]); /* show that the struct was 0 */
printf("%5lu%5l u\n", sizeof array, sizeof st_arr);
*((arr *)array) = st_arr; /* assign the struct to the local array */
printf("%5d\n", array[0]); /* show that it worked */
return 0;
}
C makes arrays difficult. Their expression results in a pointer to its
first element, they cannot be passed by value. Shucks. But what of a
struct consisting of an array? You can do anything with the struct that
you can with the array. What I have not realized until today is, you can
assign the 'value' of a struct (the whole thing) to a local array of the
same size (carefully), as above.

*((arr *)array) = st_arr; /* assign the struct to the local array */

This works (I think) because array in this context is pointer. Casting
it to a struct pointer and dereferencing it creates perfect lvalue
target for the assignment of a struct.

Have I been asleep all these years? Have I made a new discovery? Thanks
Ed.
--
Joe Wright mailto:joewwrig ht@earthlink.ne t
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[Thomas Pfaff]

Re: Clearing an array

Joe Wright <joewwright@ear thlink.net> writes:[color=blue]
> C makes arrays difficult. Their expression results in a pointer to its
> first element, they cannot be passed by value.[/color]

Well since the value of an array is a pointer to its initial element,
I'd say arrays are indeed being passed by value ;-)

[Martin Dickopp]

Re: Clearing an array

Thomas Pfaff <thomas.pfaff@t iscali.no> writes:
[color=blue]
> Lew.Pitcher@td. com (Lew Pitcher) writes:
>[color=green]
> > #include <string.h>
> >
> > memset(Buffer, 0, sizeof Buffer);[/color]
>
> That's not guaranteed to work unless `Buffer' is of type unsigned char, is it?[/color]

As you correctly point out elsewhere in this thread, it is guaranteed to
work for all integer types according to Defect Report #263. :)

Martin