segfault on strtok

[Fatih Gey]

Hi,

.. following causes a segfault. .. didn't
know why ?!

int main() {
char name[15];
strcpy (name, "ab8bc8cd8e d");

char cur[800];
strcpy (cur, strtok(name, "8"));

while (cur) {
printf ("Output: %s\n", cur);
printf ("Stringleng th %i\n", strlen(cur));
strcpy(cur,strt ok(0, "8"));
printf ("next\n");
}

}

output: -----------------------

Output: ab
Stringlength 2
next
Output: bc
Stringlength 2
next
Output: cd
Stringlength 2
next
Output: ed
Stringlength 2
Segmentationfau lt
------------------------------

Thanks for any help
Regards
Fatih Gey

[Andreas Kahari]

In article <bn************ *@news.t-online.com>, Fatih Gey wrote:
[cut]

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

int main() {
char name[15];
strcpy (name, "ab8bc8cd8e d");

char cur[800];
strcpy (cur, strtok(name, "8"));

while (cur) {
cur is never going to be zero.
printf ("Output: %s\n", cur);
printf ("Stringleng th %i\n", strlen(cur));
strcpy(cur,strt ok(0, "8"));
(strictly speaking, the zero on that line should be a null
pointer)
printf ("next\n");
}

}

Check the return value of strtok(). It returns NULL when no
more tokens remains. NULL is defined in <stdlib.h>.

Cheers,
Andreas
--
Andreas Kähäri

[Kevin Goodsell]

Andreas Kahari wrote:

In article <bn************ *@news.t-online.com>, Fatih Gey wrote:

printf ("Output: %s\n", cur);
printf ("Stringleng th %i\n", strlen(cur));
strcpy(cur,strt ok(0, "8"));

(strictly speaking, the zero on that line should be a null
pointer)

0 converted to a pointer *is* a null pointer. There's nothing wrong with
using 0 here.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

[pete]

Andreas Kahari wrote:

In article <bn************ *@news.t-online.com>, Fatih Gey wrote:
[cut]

#include <stdio.h>
#include <string.h> NULL is defined in <stdlib.h>.

NULL is also defined in stdio.h and string.h,
as well as in other header files.

stddef.h has the NULL macro and the _t typedefs.
NULL and all of the other macros and typedefs,
are also defined in each header file that has a prototype
for any function, which is defined as either
being able to accept them [NULL and friends], as arguments,
or return them as values.

--
pete

[Andreas Kahari]

In article <3F***********@ mindspring.com> , pete wrote:

Andreas Kahari wrote:

[cut]

NULL is defined in <stdlib.h>.

NULL is also defined in stdio.h and string.h,
as well as in other header files.

Ah, yes.
--
Andreas Kähäri

[Andreas Kahari]

In article
<Ol************ ****@newsread4. news.pas.earthl ink.net>, Kevin
Goodsell wrote:

Andreas Kahari wrote:

[cut]

(strictly speaking, the zero on that line should be a null
pointer)

0 converted to a pointer *is* a null pointer. There's nothing wrong with
using 0 here.

Yes, the integer zero is a null pointer, but only if it's cast
to void * and converted into a pointer type. Besides, it looks
better if one says NULL where one means NULL.

--
Andreas Kähäri

[Sheldon Simms]

On Thu, 23 Oct 2003 23:35:08 +0000, Andreas Kahari wrote:

In article
<Ol************ ****@newsread4. news.pas.earthl ink.net>, Kevin
Goodsell wrote:

Andreas Kahari wrote:

strcpy(cur,strt ok(0, "8"));
(strictly speaking, the zero on that line should be a null
pointer)
0 converted to a pointer *is* a null pointer. There's nothing wrong with
using 0 here.

Yes, the integer zero is a null pointer, but only if it's cast
to void * and converted into a pointer type.

The first argument to strtok() above is not "the integer zero". It
is a null pointer constant and there is no need to cast it to
void *

In fact, NULL is often defined like this:

#define NULL 0
Besides, it looks better if one says NULL where one means NULL.

That is a matter of opinion.

[Fatih Gey]

>

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

int main() {
char name[15];
strcpy (name, "ab8bc8cd8e d");

char cur[800];
strcpy (cur, strtok(name, "8"));

while (cur) {

cur is never going to be zero.

printf ("Output: %s\n", cur);
printf ("Stringleng th %i\n", strlen(cur));
strcpy(cur,strt ok(0, "8"));

(strictly speaking, the zero on that line should be a null
pointer)

printf ("next\n");
}

}

Check the return value of strtok(). It returns NULL when no
more tokens remains. NULL is defined in <stdlib.h>.

ok .. i added the both include-lines, changed
while (cur) {
in
while (cur != NULL) {
and replaced 0 with NULL in subsequenced strtok-func, but it keeps
producing segfaults :-(

I think, the problem causes when while run last time and strtok returns
NULL. Is there anything wrong with strcpy-ing this NULL pointer to var
"cur" ? (see also the output-wrap in first msg of thread)
Fatih Gey

[Andreas Kahari]

In article <bn************ *@news.t-online.com>, Fatih Gey wrote:
[cut]

ok .. i added the both include-lines, changed
while (cur) {
in
while (cur != NULL) {
and replaced 0 with NULL in subsequenced strtok-func, but it keeps
producing segfaults :-(

I think, the problem causes when while run last time and strtok returns
NULL. Is there anything wrong with strcpy-ing this NULL pointer to var
"cur" ? (see also the output-wrap in first msg of thread)

Yes, that's a problem since strcpy() will probably try to
dereference the opinters given to it, and you can't dereference
a NULL pointer. Assign the retun value from strtok() to a char
pointer and check its value before using it with strcpy().
--
Andreas Kähäri

[pete]

Andreas Kahari wrote:

Yes, the integer zero is a null pointer, but only if it's cast
to void * and converted into a pointer type.

A constant expression with a value of zero,
is called a "null pointer constant"
(you can find that phrase in the standard),
whther or not it's cast to (void*).

--
pete