Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Programming > C Programming > Program repeats itself, pointer trouble I suspect.

Reply
Thread Tools

Program repeats itself, pointer trouble I suspect.

 
 
Neil
Guest
Posts: n/a
 
      02-16-2007
On Feb 14, 7:24 pm, Barry Schwarz <(E-Mail Removed)> wrote:
> On 14 Feb 2007 16:50:11 -0800, "Neil" <(E-Mail Removed)> wrote:
>
>
>
>
>
> >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

 
Reply With Quote
 
 
 
 
Neil
Guest
Posts: n/a
 
      02-16-2007
On Feb 15, 7:56 am, Ben Bacarisse <(E-Mail Removed)> wrote:
> "Neil" <(E-Mail Removed)> writes:
> > #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


 
Reply With Quote
 
 
 
 
Neil
Guest
Posts: n/a
 
      02-16-2007
On Feb 14, 8:45 pm, "Beej" <(E-Mail Removed)> wrote:
> On Feb 14, 4:50 pm, "Neil" <(E-Mail Removed)> wrote:
>
> > 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.

 
Reply With Quote
 
Ben Bacarisse
Guest
Posts: n/a
 
      02-16-2007
"Old Wolf" <(E-Mail Removed)> writes:

> On Feb 16, 12:46 pm, Ben Bacarisse <(E-Mail Removed)> wrote:
>> "Old Wolf" <(E-Mail Removed)> writes:
>> > 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.
 
Reply With Quote
 
Neil
Guest
Posts: n/a
 
      02-16-2007
On Feb 14, 7:24 pm, Barry Schwarz <(E-Mail Removed)> wrote:
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



 
Reply With Quote
 
Neil
Guest
Posts: n/a
 
      02-16-2007
On Feb 15, 7:18 pm, "Neil" <(E-Mail Removed)> wrote:
> On Feb 14, 7:24 pm, Barry Schwarz <(E-Mail Removed)> wrote:
> 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


 
Reply With Quote
 
Neil
Guest
Posts: n/a
 
      02-16-2007
On Feb 14, 9:00 pm, Christopher Layne <(E-Mail Removed)> wrote:
> 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..........but OK.
I'll try that.
Thanks Chris..
-Neil

 
Reply With Quote
 
Barry Schwarz
Guest
Posts: n/a
 
      02-16-2007
On 15 Feb 2007 18:18:01 -0800, "Neil" <(E-Mail Removed)> wrote:

>On Feb 14, 7:24 pm, Barry Schwarz <(E-Mail Removed)> wrote:
>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
 
Reply With Quote
 
Neil
Guest
Posts: n/a
 
      02-16-2007
On Feb 15, 9:28 pm, Barry Schwarz <(E-Mail Removed)> wrote:
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


 
Reply With Quote
 
Richard Heathfield
Guest
Posts: n/a
 
      02-16-2007
Neil said:

> On Feb 15, 9:28 pm, Barry Schwarz <(E-Mail Removed)> wrote:
> 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.
 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
HTTP_ACCEPT_LANGUAGE; repeats and repeats value; ie recent update? cate Javascript 1 06-14-2010 03:30 PM
ASP.NET 2.0 - browser refresh repeats operation Amelyan ASP .Net 2 12-19-2005 02:45 AM
Number of times number repeats viuxrluxvbbc@mailinator.com C++ 4 12-07-2005 07:46 PM
Newbee : Can a Repeater repeats ascx control ? Mick ASP .Net 1 11-29-2004 01:41 PM
Refresh repeats last action kj12345 ASP .Net 3 09-29-2004 07:57 AM



Advertisments