Program repeats itself, pointer trouble I suspect.

[Neil]

Hello all!
I wrote program with a array of pointers, and I suspect they are
pointing at each other in the Do ...While loop.
Something is messed up with the increment variable word. A program
clip of what I'm talking about.

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

int main(void)
{
char string[50] = {"Have a nice day folks"};
char *line_ptr;
char *list[20] = { '\0' }; //Initialize the array of pointers to
NULL.
int word = 0;

line_ptr = strtok(string, " ");

do
{
list[word] = line_ptr;
word++;
line_ptr = strtok(NULL," ");
} while (line_ptr != NULL);

return 0;
}
It's kinda weird, cause the program repeats itself when I run it. I
left out the output section, cause I know it works fine. In the
debugger it works OK. Is there a memory leak? Do you need to assign
pointers to NULL after you use them? Should I free up the memory from
the array of pointers before the program terminates? What is the best
way handle pointers after your done with them?

Thanks for all your help
Neil

[Neil]

On Feb 14, 7:24 pm, Barry Schwarz <schwa...@doezl .netwrote:

On 14 Feb 2007 16:50:11 -0800, "Neil" <neilwrit...@ho tmail.comwrote:

Hello all!

I wrote program with a array of pointers, and I suspect they are
pointing at each other in the Do ...While loop.
Something is messed up with the increment variable word. A program
clip of what I'm talking about.

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

int main(void)
{
char string[50] = {"Have a nice day folks"};
char *line_ptr;
char *list[20] = { '\0' }; //Initialize the array of pointers to
NULL.

This is why you should not use // style comments in usenet.

If you want assign each of the 20 pointer in the array the NULL value,
use NULL. While 0 and '\0' will both work, they are visually
misleading. Someone might be tempted to think that the pointers point
to a char containing '\0'.

int word = 0;

line_ptr = strtok(string, " ");

do
{
list[word] = line_ptr;
word++;
line_ptr = strtok(NULL," ");
} while (line_ptr != NULL);

return 0;
}
It's kinda weird, cause the program repeats itself when I run it. I
left out the output section, cause I know it works fine. In the

Define repeat.

It starts again from main(), There must be problem elsewhere.
-Neil

[Neil]

On Feb 15, 7:56 am, Ben Bacarisse <ben.use...@bsb .me.ukwrote:

"Neil" <neilwrit...@ho tmail.comwrites :

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

int main(void)
{
char string[50] = {"Have a nice day folks"};
char *line_ptr;
char *list[20] = { '\0' }; /* Initialize the array of pointers to NULL.*/
int word = 0;

line_ptr = strtok(string, " ");

do
{
list[word] = line_ptr; /* MARK */
word++;
line_ptr = strtok(NULL," ");
} while (line_ptr != NULL);

Other than and hint in a reply to another reply, no one has pointed
out that you are in danger of accessing outside the bounds of your
array "list".

If it reasonable (is it ever?) to simply discard tokens that don't
fit, you can write:

if (word < 20) list[word] = line_ptr;

where I put /* MARK */ in your code.

I don't know of this is the source of your problem, because the
description is rather vague.

--
Ben.- Hide quoted text -

- Show quoted text -

Ben your probably right, but I didn't want to go through whole
program, just the code clip I
mentioned. Thanks for the help, I'll try that....

-Neil

[Neil]

On Feb 14, 8:45 pm, "Beej" <[e-mail] ote:

On Feb 14, 4:50 pm, "Neil" <neilwrit...@ho tmail.comwrote:

line_ptr = strtok(string, " ");

Unless you're sure you're always going to have a token, you should
probably check line_ptr for NULL here, too.

Here's a compact form of that, if you don't mind assignments in your
expressions:

if ((p = strtok(string, " ")) != NULL) {
do {
printf("Token: %s\n", p);
} while ((p = strtok(NULL, " ")) != NULL);

}

do
{
list[word] = line_ptr;
word++;
line_ptr = strtok(NULL," ");
} while (line_ptr != NULL);

Here is my output when I ran it.

'Have'
'a'
'nice'
'day'
'folks'

Looks fine to me. What's your output?

-Beej

Beej the output section is a function that I left off, however the
program does begin
at the start, or the program crashes, from what I tried recently.
I'm trying to isolate the problem. thanks.
-Neil.

[Ben Bacarisse]

"Old Wolf" <ol*****@inspir e.net.nzwrites:

On Feb 16, 12:46 pm, Ben Bacarisse <ben.use...@bsb .me.ukwrote:

>"Old Wolf" <oldw...@inspir e.net.nzwrites:

Are you perhaps referring to the fact that the program might
break if its source is modified to introduce a bug, as
suggested by Ben Bacarisse?

I'm not seeing it. Can you post a correction to my message (or
explain it to me and I'll post a correction)?

Your message appears to be saying that the program could
break if the input string were modified to have more than
20 words in it, which would be a bug. But the original
post only had 4 words in the string, so there is no problem.

Ah, OK. Crossed wires.

(Of course it is not a bad idea to add in checking, as
you suggested).

....but probably not in any way a fix for the OP's problem if it failed
with a four token string.

--
Ben.

[Neil]

On Feb 14, 7:24 pm, Barry Schwarz <schwa...@doezl .netwrote:
This is why you should not use // style comments in usenet.
Huh?....Didn't know that.

Barry, I'm using an old Borland Turbo C++ for DOS Compiler to write
this program, it's crashed a couple of times writing I what I think
what looks like elementry code.

If you don't intialize a pointer, but you declared it main() and just
leave it.
Does this present a problem after the program terminates?

Can two char pointers in an array of pointers point to each other
after the program terminates?

Thanks for tip..

-Neil

[Neil]

On Feb 15, 7:18 pm, "Neil" <neilwrit...@ho tmail.comwrote:

On Feb 14, 7:24 pm, Barry Schwarz <schwa...@doezl .netwrote:
This is why you should not use // style comments in usenet.

Huh?....Didn't know that.

Barry, I'm using an old Borland Turbo C++ for DOS Compiler to write
this program, it's crashed a couple of times writing I what I think
what looks like elementry code.

If you don't intialize a pointer, but you declared it main() and just
leave it.

I ment inside main() :)

-Neil

[Neil]

On Feb 14, 9:00 pm, Christopher Layne <[e-mail] dizedwrote:

Neil wrote:

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

int main(void)
{
char string[50] = {"Have a nice day folks"};
char *line_ptr;
char *list[20] = { '\0' }; //Initialize the array of pointers to

Cleaner version:

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

enum constants {
STRING_MAX = 50,
WORD_MAX = 20

};

int main(void)
{
char string[STRING_MAX] = "Have a nice day folks";
char *word[WORD_MAX];
int i;

for (i = 0; i < WORD_MAX; i++) {
if ((word[i] = strtok(i ? NULL : string, " ")) == NULL)
break;
fprintf(stdout, "word[%d] = %s\n", i, word[i]);
}

return 0;

Huh? ........Better then mine..........b ut OK.
I'll try that.
Thanks Chris..
-Neil

[Barry Schwarz]

On 15 Feb 2007 18:18:01 -0800, "Neil" <ne*********@ho tmail.comwrote:

>On Feb 14, 7:24 pm, Barry Schwarz <schwa...@doezl .netwrote:
This is why you should not use // style comments in usenet.
Huh?....Didn 't know that.

Barry, I'm using an old Borland Turbo C++ for DOS Compiler to write
this program, it's crashed a couple of times writing I what I think
what looks like elementry code.

Post a compilable example of the code that exhibits the behavior.

>
If you don't intialize a pointer, but you declared it main() and just
leave it.
Does this present a problem after the program terminates?

Unless you attempt to evaluate its value, the fact that a pointer is
uninitialized (technically called indeterminate) cannot be a problem.

>
Can two char pointers in an array of pointers point to each other
after the program terminates?

Unless you have a very strange operating system, after your program
terminates none of your objects exist. Since they no longer exist,
one of the many things they don't do is point anywhere, let alone to
each other.

While your program is running, it is still not possible for one char
pointer to point to another. By definition, a char pointer must point
to a char (if it points anywhere). It makes no difference whether the
pointers are in an array or not.
Remove del for email

[Neil]

On Feb 15, 9:28 pm, Barry Schwarz <schwa...@doezl .netwrote:
Post a compilable example of the code that exhibits the behavior.

Barry, I would if I knew where the problem is in the program..
Obviouly the pointers are not causing the problem.

Thanks for all your help
-Neil

[Richard Heathfield]

Neil said:

On Feb 15, 9:28 pm, Barry Schwarz <schwa...@doezl .netwrote:
Post a compilable example of the code that exhibits the behavior.

Barry, I would if I knew where the problem is in the program..

If you knew where the problem was, you wouldn't need to ask about it at
all. Since you don't know where the problem was, it makes sense to post
the whole program.

Obviouly the pointers are not causing the problem.

But you just said you don't know where the problem is.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at the above domain, - www.