what's wrong with my code of linked list?

[questions?]

I am testing a problem with linked list.
I just do a lot of times: create a list, then free it.

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

struct element {
int index;
struct element *next;
};

void free_list(struct element * first){
struct element *current,*next;
current=first;
next=current->next;
while(next !=NULL){
printf("free the %d the element\n",current->index);
free(current);
current=next;
next=current->next;
}
free(current);
}

void print_list(struct element *first){
struct element *current;
current=first;
while(current !=NULL){
printf("the %d th element visited\n",current->index);
current=current->next;
}
}
struct element *create_list(void){
struct element *temp,*leading,*previous;
int i;
leading=malloc(sizeof(struct element));
leading->index=0;
previous=leading;

for(i=1;i<1000;i++){
temp=malloc(sizeof(struct element));
temp->next==NULL;
temp->index=i;
previous->next=temp;
previous=temp;
}
return leading;
}

int main(){
int i;
struct element *dummy;
for(i=0;i<2;i++){
dummy=create_list();
print_list(dummy);
free_list(dummy);
}
return 0;
}

************************************************** ****
What's wrong this this code? it is fine when I use for(i=0;i<1;i++) in
main().

Thanks

[Simple Simon]

un************@hotmail.com wrote...

temp->next==NULL;

[Keith Thompson]

"questions?" <un************@hotmail.com> writes:

I am testing a problem with linked list.
I just do a lot of times: create a list, then free it.

#############################################
# include <stdio.h>
# include <stdlib.h> [snip]
************************************************** ****
What's wrong this this code? it is fine when I use for(i=0;i<1;i++) in
main().

You're going to have to give us a hint. What is the program supposed
to do, and what does it actually do?

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Richard Bos]

"questions?" <un************@hotmail.com> wrote:

I am testing a problem with linked list.
I just do a lot of times: create a list, then free it.

#############################################
[ Snip linked list code ]
************************************************** ****
What's wrong this this code? it is fine when I use for(i=0;i<1;i++) in
main().

What's your problem with it? It runs fine for me, and at first glance I
can't find anything wrong with it. The only nit I would pick is that
what you call "leading" is conventionally called the head node, but
that's not an actual error, it's a style issue.

Richard

[Richard Bos]

Simple Simon <ss****@domain.invalid> wrote:

un************@hotmail.com wrote...

temp->next==NULL;

Argh! That's what's wrong with first glances: they miss the obvious...

Richard

[Michael Rasmussen]

On Wed, 29 Mar 2006 23:28:26 -0800, questions? wrote:

A minor glitch

temp->next==NULL;

temp->next = NULL;

Try next time to add this option to your compile statement: -Wall
Then you would have received this warning:
test.c: In function 'create_list':
test.c:41: warning: statement with no effect

--
Hilsen/Regards
Michael Rasmussen
http://keyserver.veridis.com:11371/p...rch=0xE3E80917

[Marek Dzikiewicz]

questions? wrote:

void free_list(struct element * first){
struct element *current,*next;
current=first;
next=current->next;

This is illegal if the list is empty (next == NULL).

[Chris Torek]

Others already picked out various nits.

In article <11**********************@v46g2000cwv.googlegroups .com>,
questions? <un************@hotmail.com> wrote:

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

struct element {
int index;
struct element *next;
};
I usually put the forward link first, not that it matters much in
this case. Also, I like to use the macros from the BSD <sys/queue.h>
headers, but that might be overkill in this case.
void free_list(struct element * first){
struct element *current,*next;
current=first;
next=current->next;
while(next !=NULL){
printf("free the %d the element\n",current->index);
free(current);
current=next;
next=current->next;
}
free(current);
}
To avoid redundant code and problems with freeing an empty list
and so on, I prefer to write:

void free_list(struct element *head) {
struct element *p, *next;

for (p = head; p != NULL; p = next) {
next = p->next;
free(p);
}
}
void print_list(struct element *first){
struct element *current;
current=first;
while(current !=NULL){
printf("the %d th element visited\n",current->index);
current=current->next;
}
}
Again, I would use a "for" loop; this time the match is so good
that we do not even need a separate "next" variable:

for (p = head; p != NULL; p = p->next)
printf("...\n", p->...);
struct element *create_list(void){

[contents snipped]

Here is where the BSD macros become particularly handy.

In general, I find that the list elements themselves might be
created with a "factory" (to steal a term more often applied to
OO-ish languages like C++). If the list is ordered in some
way, and/or if list-elements might be on multiple lists --
"every element in the entire system" but also "parent/child"
relationships with sibling and grandchild nodes and so forth,
and perhaps hash lists and timer queues and on and on -- I
can use the BSD macros to embed multiple "list" or "queue"
points inside each element.

Then, I can have multiple queue heads of various sorts, and
use TAILQ_APPEND, CIRCLEQ_INSERT_AFTER, and so on to do the
list manipulation.

Each type of queue has particular features and costs, as summarized
in the queue(3) manual (q.v.; use google).
--
In-Real-Life: Chris Torek, Wind River Systems
Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W) [phone]
email: forget about it http://web.torek.net/torek/index.html
Reading email is like searching for food in the garbage, thanks to spammers.

[August Karlstrom]

Simple Simon wrote:

un************@hotmail.com wrote...

temp->next==NULL;

One more item to add to the "Case Against C" list. ;-)
August

--
I am the "ILOVEGNU" signature virus. Just copy me to your
signature. This email was infected under the terms of the GNU
General Public License.

[Richard Tobin]

In article <gm*******************@newsb.telia.net>,
August Karlstrom <fu********@comhem.se> wrote:

temp->next==NULL;

One more item to add to the "Case Against C" list. ;-)

A reasonable compiler will warn you about this.

-- Richard

[August Karlstrom]

Richard Tobin wrote:

In article <gm*******************@newsb.telia.net>,
August Karlstrom <fu********@comhem.se> wrote:

temp->next==NULL;

One more item to add to the "Case Against C" list. ;-)

A reasonable compiler will warn you about this.

Yes, you're right. It's unfortunate however that "no warnings" are
usually the default setting.
August

--
I am the "ILOVEGNU" signature virus. Just copy me to your
signature. This email was infected under the terms of the GNU
General Public License.

[Ben Pfaff]

August Karlstrom <fu********@comhem.se> writes:

Richard Tobin wrote:

A reasonable compiler will warn you about this.

Yes, you're right. It's unfortunate however that "no warnings" are
usually the default setting.

A reasonable programmer quickly learns to enable warnings :-)
--
"C has its problems, but a language designed from scratch would have some too,
and we know C's problems."
--Bjarne Stroustrup

[questions?]

Ben Pfaff wrote:

August Karlstrom <fu********@comhem.se> writes:

Richard Tobin wrote:

A reasonable compiler will warn you about this.

Yes, you're right. It's unfortunate however that "no warnings" are
usually the default setting.

A reasonable programmer quickly learns to enable warnings :-)
--
"C has its problems, but a language designed from scratch would have some too,
and we know C's problems."
--Bjarne Stroustrup

Thanks you all for a lot of good discussions.
I made an error in that line of ==.
I was trying to mimic what I did in my bigger program by giving a
simple example.
The error actually is not happening in the construct/free list process.

I found the package valgrind really helpful for finding errors.