printing values of "arrays of pointers"

[arnuld]

PURPOSE: see the comments.
WHAT I GOT: infinite loop

/* This program will simply create an array of pointers to integers
* and will fill it with some values while using malloc to create
* pointers to fill the array and then will print the values pointed
* by those pointers
*
*/

#include <stdio.h>
#include <stdlib.h>

enum MAXSIZE { ARRSIZE = 100 };
int main( void )
{
int* arr_p[ARRSIZE];
int** pp;
int *mp, *np;
int i;

int null_int = 0;

pp = arr_p;
np = &null_int;
for( i = 0; i < ARRSIZE - 1; ++i )
{
mp = malloc( sizeof( int ) );
mp = &i;
arr_p[i] = mp;
}
arr_p[i] = np;

while( **pp )
{
printf("**pp = %d\n", **pp);
}

return 0;
}

--
http://lispmachine.wordpress.com/
my email ID is @ the above address

[Richard Heathfield]

arnuld said:

PURPOSE: see the comments.
WHAT I GOT: infinite loop

/* This program will simply create an array of pointers to integers
* and will fill it with some values while using malloc to create
* pointers to fill the array and then will print the values pointed
* by those pointers
*
*/

#include <stdio.h>
#include <stdlib.h>

enum MAXSIZE { ARRSIZE = 100 };
int main( void )
{
int* arr_p[ARRSIZE];
int** pp;
int *mp, *np;
int i;

int null_int = 0;

pp = arr_p;
np = &null_int;
for( i = 0; i < ARRSIZE - 1; ++i )
{
mp = malloc( sizeof( int ) );

You don't check to see whether this fails to allocate the requested
memory...

mp = &i;

....which doesn't really matter, since you throw it away here.

arr_p[i] = mp;
}

Well done. You just filled arr_p with a bunch of pointers to i. Why bother
with the malloc call, then? You could save yourself (ARRSIZE-1) *
sizeof(int) bytes of memory leak by removing the malloc call completely.

arr_p[i] = np;

while( **pp )

pp has the value &arr_p[0], so **pp attempts to find the int value at
*arr_p[0]. Since arr_p[0] points to i, we're looking for the value of i.
That value is indeterminate, because the object i never had a value
assigned to it. Thus, the behaviour is undefined. This loop could execute
forever (the most likely possibility) or not at all (probably the second
most likely) or something completely weird could happen.

{
printf("**pp = %d\n", **pp);
}

You don't even /try/ to iterate through the array, do you? You might want
to take a long hard look at Visual Basic or RCX.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[arnuld]

On Fri, 02 May 2008 13:44:50 +0000, Richard Heathfield wrote:

> for( i = 0; i < ARRSIZE - 1; ++i )
{
mp = malloc( sizeof( int ) );

You don't check to see whether this fails to allocate the requested
memory...

done

> mp = &i;

...which doesn't really matter, since you throw it away here.

well, then how can I generate a new variable every-time I enter into the
loop ?

Well done. You just filled arr_p with a bunch of pointers to i. Why bother
with the malloc call, then? You could save yourself (ARRSIZE-1) *
sizeof(int) bytes of memory leak by removing the malloc call completely.

I can but I did not because I want to understand the how pointers to
arrays to pointers behave and learn them.

You don't even /try/ to iterate through the array, do you?

okay, here is a little fixed version. I can't do anything about variable i
in for loop as I said, I can't find a way to generate new variables at
every iteration through the loop.

You might want to take a long hard look at Visual Basic

http://lispmachine.wordpress.com/200...urn-for-vbnet/

or RCX.

never heard of it
--
http://lispmachine.wordpress.com/
my email ID is @ the above address

[Bartc]

"arnuld" <No****@microso ft.comwrote in message
news:pa******** *************** *****@microsoft .com...

PURPOSE: see the comments.
WHAT I GOT: infinite loop

I've modified your code so that it behaves better:
#include <stdio.h>
#include <stdlib.h>

enum MAXSIZE { ARRSIZE = 100 };
int main( void )
{
int *arr_p[ARRSIZE];
int **pp;
int *np;
int i;

int null_int = 0;

pp = arr_p;
np = &null_int;
for( i = 0; i < ARRSIZE - 1; ++i )
{
arr_p[i] = malloc( sizeof( int ) );
*arr_p[i] = 1000+i; /* initial the ints to some recognisable
(and non-0!) value */
}
arr_p[i] = np; /* sentinel (*np contains 0) */

while( **pp) /* Step through array using pp */
{
printf("**pp = %d\n", **pp);
++pp;
}

return 0;
}

-- Bartc

[Ben Bacarisse]

[BTW, there seems to be somthing odd in the way you newsreader add
attribution lines. I've fixed it, I think.]

arnuld <No****@microso ft.comwrites:

On Fri, 02 May 2008 13:44:50 +0000, Richard Heathfield wrote:

>> for( i = 0; i < ARRSIZE - 1; ++i )
{
mp = malloc( sizeof( int ) );

>You don't check to see whether this fails to allocate the requested
memory...

done

>> mp = &i;

>...which doesn't really matter, since you throw it away here.

well, then how can I generate a new variable every-time I enter into the
loop ?

That is what malloc is for. C calls them objects, and you make them
exactly as you have written it. The error is overwriting the pointer
you get from malloc with one to i. Pointers to local variables like
i (automatic storage in C terms) are very rarely used.

--
Ben.

[pete]

arnuld wrote:

PURPOSE: see the comments.
WHAT I GOT: infinite loop

/* This program will simply create an array of pointers to integers
* and will fill it with some values while using malloc to create
* pointers to fill the array and then will print the values pointed
* by those pointers
*
*/

#include <stdio.h>
#include <stdlib.h>

enum MAXSIZE { ARRSIZE = 100 };
int main( void )
{
int* arr_p[ARRSIZE];
int** pp;
int *mp, *np;
int i;

int null_int = 0;

pp = arr_p;
np = &null_int;
for( i = 0; i < ARRSIZE - 1; ++i )
{
mp = malloc( sizeof( int ) );
mp = &i;
arr_p[i] = mp;
}
arr_p[i] = np;

while( **pp )
{
printf("**pp = %d\n", **pp);
}

return 0;
}

/* BEGIN new.c */
/*
** This program will simply create an array of pointers to integers
** and will fill it with some values while using malloc to create
** pointers to fill the array and then will print the values pointed
** by those pointers
*/
#include <stdio.h>
#include <stdlib.h>

#define MAXSIZE 100

void free_ptrs(int **p, size_t n);

int main(void)
{
int i;
int *arr_p[MAXSIZE];
int **pp;

puts("/* BEGIN new.c output */\n");
for (i = 0; i < MAXSIZE - 1; ++i ) {
arr_p[i] = malloc(sizeof *arr_p[i]);
if (arr_p[i] == NULL) {
printf("arr_p[%d] == NULL\n", i);
break;
}
*arr_p[i] = i;
}
arr_p[i] = NULL;
for (pp = arr_p; *pp != NULL; ++pp) {
printf("**pp = %d\n", **pp);
}
free_ptrs(arr_p , i);
puts("\n/* END new.c output */");
return 0;
}

void free_ptrs(int **p, size_t n)
{
while (n-- != 0) {
free(*p);
*p++ = NULL;
}
}

/* END new.c */

--
pete

[Bartc]

"santosh" <sa*********@gm ail.comwrote in message
news:fv******** **@registered.m otzarella.org.. .

arnuld wrote:

Path: news.motzarella .org!motzarella .org!newsfeed.s traub-nv.de!
goblin1!goblin2 !goblin.stu.nev a.ru!news.net.u ni-c.dk!dotsrc.org !
filter.dotsrc.o rg!news.dotsrc. org!not-for-mail
From: arnuld <No****@microso ft.com>

You have no legal right to use that email address unless you are an
employee of Microsoft and have received their permission to do so.

Don't know the OP's newsreader but: if you open a news account with Outlook
Express, it does ask:

"Email address: ..... for example: so*****@microso ft.com"

Could someone really be sued for following this advice too literally?

-- Bartc

[Richard Tobin]

In article <fv**********@r egistered.motza rella.org>,
santosh <sa*********@gm ail.comwrote:

>You have no legal right to use that email address unless you are an
employee of Microsoft and have received their permission to do so.

Do you have any basis for this claim? I don't recall any laws being
passed on the subject. Trademark law isn't relevant, since he's not
engaged in trade. He is clearly not using their name for any
fraudulent purpose. He's not misrepresenting himself (even if that
were illegal) since no-one would take it as a real email address.
RFCs have no legal force.

Nothing stops me from going around wearing a badge saying "Bill Gates,
Microsoft", unless I do it for some illegal purpose. Why should a
header in a news posting be any different?

At most he might be violating his ISP's terms and conditions.

-- Richard
--
:wq

[santosh]

Richard Tobin wrote:

In article <fv**********@r egistered.motza rella.org>,
santosh <sa*********@gm ail.comwrote:

>>You have no legal right to use that email address unless you are an
employee of Microsoft and have received their permission to do so.

Do you have any basis for this claim? I don't recall any laws being
passed on the subject. Trademark law isn't relevant, since he's not
engaged in trade. He is clearly not using their name for any
fraudulent purpose. He's not misrepresenting himself (even if that
were illegal) since no-one would take it as a real email address.
RFCs have no legal force.

Nothing stops me from going around wearing a badge saying "Bill Gates,
Microsoft", unless I do it for some illegal purpose. Why should a
header in a news posting be any different?

At most he might be violating his ISP's terms and conditions.

I don't know about other countries, but I believe we have rules in our
so-called "Cyber Laws" that prohibit willfull impersonation and
misrepresentati on. This would be particularly applicable if arnuld were
to comment upon Microsoft under this false email address. And why would
no one take it as a real email address? It's a perfectly valid domain
and hostname, though the latter may not exist. It's not a proper munged
address, nor an invalid address.

More practically Sunsite could terminate his account with them if they
were to be alerted to his behaviour. Their rules clearly say that users
are only to use their own email addresses which actually exist and can
be delivered to, in the Sender field.

[Flash Gordon]

santosh wrote, On 03/05/08 11:51:

Richard Tobin wrote:

>In article <fv**********@r egistered.motza rella.org>,
santosh <sa*********@gm ail.comwrote:

>>You have no legal right to use that email address unless you are an
employee of Microsoft and have received their permission to do so.

Do you have any basis for this claim? I don't recall any laws being
passed on the subject. Trademark law isn't relevant, since he's not

<snip>

I don't know about other countries, but I believe we have rules in our
so-called "Cyber Laws" that prohibit willfull impersonation and
misrepresentati on. This would be particularly applicable if arnuld were
to comment upon Microsoft under this false email address. And why would
no one take it as a real email address? It's a perfectly valid domain
and hostname, though the latter may not exist. It's not a proper munged
address, nor an invalid address.

Also some of us (well, me anyway) deliberately use addresses in our
domains that look like spamtraps. I've found that spam@ gets spammed
less than other addresses I've used.

More practically Sunsite could terminate his account with them if they
were to be alerted to his behaviour. Their rules clearly say that users
are only to use their own email addresses which actually exist and can
be delivered to, in the Sender field.

Ah well, I'm sure at some point someone will decide to report him to
them if he continues.
--
Flash Gordon