I think I have gotten that part down thanks.
How I would un append that list.
---------- Post updated at 01:30 PM ---------- Previous update was at 01:22 PM ----------
I mean will the code below work if descr_list is a global variable?
Code:
int readjust_descr()
{
struct descr *l;
struct descr *r;
for(l = descr_list; l; l = l->next)
{
if (l->state == 0)
{
r = l;
l = l->next;
free(r);
}
}
}
---------- Post updated at 01:32 PM ---------- Previous update was at 01:30 PM ----------
I'm iffy on wether that will work or not because I thought pointers work differently.
Meaning I am worried that if r = l; and then l = l->next, then r will be pointing to
l->next and I will be freeing l->next when I free r.
---------- Post updated at 01:34 PM ---------- Previous update was at 01:32 PM ----------
also thanks again you've been very helpful. I have more questions to ask but I wont
ask untill I get to them.
Forget everything you know about pointers. They have no abilities to change themselves.
Code:
int array[32];
int addr1=16;
int addr2=10;
array[addr1]=5; // array[16]=5
array[addr2]=10;// array[10]=10
addr2=addr1; //addr2=16
// print position 16
printf("[addr2]=%d\n", array[addr2]);
addr2=addr1 does nothing at all to the contents of the array -- would you agree?
Code:
int initialize_descr(int newfd, int newval)
{
newval=newfd;
}
int fd=1, newval=10;
initialize_descr(fd, newval);
printf("%d\n", newval);
This will print 10, would you agree?
Pointers are just index numbers for the huge array of memory that belongs to your process. Copying them and moving them around does absolutely nothing to the contents.
Which means, this code is equivalent:
Code:
int array[32];
int *ptr1=array+16; // Points to position 16 in the array
int *ptr2=array+10; // Points to position 10 in the array
(*ptr1)=5; // Set array[16]=5
(*ptr2)=10;//Set array[10]=10
ptr2=ptr1; // ptr2 now points to position 16
// Should print the value of position 16
printf("*ptr2 = %d\n", *ptr2);
Code:
int readjust_descr()
{
struct descr *l, *r;
for(l = descr_list; l; l = l->next)
{
if (l->state == 0)
{
r = l;
l = l->next;
free(r);
}
}
}
You're getting much closer, but what happens to the descr pointing to the node you freed? It's just a number -- it doesn't change by itself just because you made a library call.
So it's still sitting there pointing to the memory you just freed. That will crash or do weird things next time you read it.
Which means you have to stop one early, so you can free the next node and tell the current node where the list ends.
Code:
void readjust_descr()
{
struct descr *l, *r;
// What if the very first node needs deleting?
while(descr_list->state == 0)
{
// This is easy: nothing but descr_list points to it.
// Save the one after it...
r=descr_list->next;
free(descr_list); // free the current...
descr_list=r; // and make descr_list point to the next.
// We've deleted the first node, and set descr_list to the next.
// If the current descr_list is also 0, we'll need to delete it too.
// That's why this is a while(), not an if().
// Except, if r was NULL, descr_list->state will now CRASH. Check first!
if(descr_list == NULL) return; // empty list, nothing left to do
}
while(l->next != NULL) // Loop until we're one from the end
{
// Check what comes next.
while(l->next->state == 0)
{
r=l->next->next; // Remember what comes after
free(l->next); // l->next now points to memory that doesn't exist!
l->next=r; // Make it point to the rest of the list instead.
// Now, how do we know the l->next we have now isn't ALSO
// zero? l=l->next will skip it! We have to check again.
// This is why this is a 'while' instead of an 'if'.
//...but if next is NULL, next->state will CRASH.
// So we have to check that too!
if(l->next == NULL) break; // End of the list! Stop!
}
l=l->next; // Move forward in the list
}
}
Last edited by Corona688; 09-29-2011 at 05:05 PM..
---------- Post updated at 03:52 AM ---------- Previous update was at 03:48 AM ----------
Does this loop through the entire descr_list?
while(descr_list->state == 0)
And why did you do this part?
while(l->next != NULL)
I feel like I'm missing something. Like cause I can't see the reason for looping
through l->next.
---------- Post updated at 03:53 AM ---------- Previous update was at 03:52 AM ----------
I'm just wondering if you did that second part just in case I want l to be iterated
through but I gotta make sure.
---------- Post updated at 05:57 AM ---------- Previous update was at 03:53 AM ----------
Ok help me with this part and I'll prolly understand the readjust_descr
function better. Ok the variables of the function here are the socket
that I will send messages to and a structure defined right before this
function is used. descr_list is a global structure descr structure posted
above the function in the code below. Ok the function works. It makes
the structure defined before it, equal to a Null part of a copy of descr_list.
My problem is the fact that I want descr_list to have struct descr *p as
a part of itself and I thought initializing a null part of d would do that but
now I am thinking that it wont.
Ok so heres a huntch I have at making the structure descr *d part of
descr_list. Maybe I just change the value adescr_list untill it is pointing to
a NULL structure and then make it equal to d. I thought maybe I'll do that at the end of initialize_descr. I'm thinking though about the descr_list
structure and if it will still point to the beginning of the list if I access it in a different function.
Code:
struct descr
{
short int newfd;
short int state; /* Maximum states allowed, 65536 */
struct queue *q;
struct descr *next;
};
int initialize_descr(int newfd, struct descr **p)
{
struct descr *d;
d = descr_list;
if( d != NULL)
{
while(d->next != NULL)
d = d->next;
if(!(d->next = malloc(sizeof(struct descr))))
{
nonfatal("malloc failure initializing descr");
return 0;
}
d = d->next;
}
else if(!(d = malloc(sizeof(struct descr))))
{
nonfatal("malloc failure initializing descr");
return 0;
}
d->newfd = newfd;
d->state = 1;
if(!(d->q = malloc(sizeof(struct descr))))
{
nonfatal("malloc failure initializing descr queue");
d->state = 0;
return 0;
}
d->q->next = NULL;
d->next = NULL;
*p = d;
}
What do I have to add to this function to make a list of player structures out of the global variable descr_list?
something like while descr_list->next != NULL descr_list= descr_list->next descr_list ->next = p. I am thinking that
that might not wrk because descr_list will now point to the structure before p and not at the very first structure
of itself.
---------- Post updated at 06:08 AM ---------- Previous update was at 05:57 AM ----------
I just don't understand.
---------- Post updated at 06:20 AM ---------- Previous update was at 06:08 AM ----------
I think I figured out a way to do this. I'll just add another structure to every
structure created by that thing that points to the first part of itself. I'm gonna post
the finished function when I'm done with it. Maybe you could look at it.
Code:
struct descr
{
short int newfd;
short int state; /* Maximum states allowed, 65536 */
struct queue *q;
struct descr *next;
struct descr *self;
};
---------- Post updated at 06:56 AM ---------- Previous update was at 06:20 AM ----------
So what do you think?
Will she work?
I think I have finally done it.
when you call free() on memory block 2, what happens to memory block 1? Absolutely nothing. It still points to memory block 2. It doesn't know it's the last node in the list! Next time you use the list it'll try to access block 2 anyway, and either crash or do strange things.
Whenever you're not at the first node in the list, you need to check and free the next node, not the current one, otherwise you'll leave dangling pointers all over the place.
Quote:
I'm just wondering if you did that second part just in case I want l to be iterated
through but I gotta make sure.
I explained exactly why I did absolutely everything in the comments I put in my code, I suggest you read them. If you don't understand my comments, ask questions about them, please don't just ignore them.
Quote:
My problem is the fact that I want descr_list to have struct descr *p as
a part of itself and I thought initializing a null part of d would do that but
now I am thinking that it wont.
If I get your meaning, it won't.
A pointer is a memory address and nothing more. Trying to initialize a NULL means trying to write to address 0 in memory, which crashes.
Since you never actually posted your data structures, I certainly can't show you how to fix them.
Quote:
Ok so heres a huntch I have at making the structure descr *d part of
descr_list. Maybe I just change the value adescr_list untill it is pointing to
a NULL structure and then make it equal to d.
Changing the pointers doesn't change the memory. Please read the examples I posted for you about array indexes.
Code:
// descr **p is pointless, returning a pointer is much less likely
// to be screwed up.
int initialize_descr(int newfd)
{
struct descr *d=descr_list;
// why are there absolutely no comments in your code?
if( d != NULL)
{
while(d->next != NULL)
d = d->next;
if(!(d->next = malloc(sizeof(struct descr))))
{
nonfatal("malloc failure initializing descr");
return 0;
}
d = d->next;
}
// We only allocate this memory when the list is empty.
// But you forgot to put it into descr_list.
// So the list will always stay empty!
else if(!(d = malloc(sizeof(struct descr))))
{
nonfatal("malloc failure initializing descr");
return 0;
}
d->newfd = newfd;
d->state = 1;
if(!(d->q = malloc(sizeof(struct descr))))
{
nonfatal("malloc failure initializing descr queue");
d->state = 0;
return 0;
}
d->q->next = NULL;
d->next = NULL;
*p = d;
}
How about:
Code:
struct descr *initialize_descr(int newfd, struct descr **p)
{
struct descr *d=descr_list;
if(d == NULL)
{
// The base of the list itself must be updated.
descr_list=malloc(sizeof(struct descr));
// then set our own pointer to it too.
d=descr_list;
// if malloc failed, return error.
if(d == NULL) return(NULL);
}
else
{
// find the end of the list.
while(d->next != NULL) d=d->next;
d->next=malloc(sizeof(struct descr));
// if malloc failed, return error
if(d->next == NULL) return(NULL);
// set d to the memory we just allocated.
d=d->next;
}
d->newfd = newfd;
d->state = 1;
if(!(d->q = malloc(sizeof(struct descr))))
{
nonfatal("malloc failure initializing descr queue");
d->state = 0;
return 0;
}
d->q->next = NULL;
d->next = NULL;
return(d);
}
Quote:
What do I have to add to this function to make a list of player structures out of the global variable descr_list?
something like while descr_list->next != NULL descr_list= descr_list->next descr_list ->next = p.
There's only two times you'd change the value of descr_list.
1) When the list is empty. descr_list must be set to the new first node.
2) When the first node is being deleted. descr_list must be set to the next node.
Code:
struct descr
{
short int newfd;
short int state; /* Maximum states allowed, 65536 */
struct queue *q;
struct descr *next;
struct descr *self;
};
If you need to add a 'self' pointer to keep your code together, you must be doing something very strange indeed.
---------- Post updated at 06:56 AM ---------- Previous update was at 06:20 AM ----------
So what do you think?
Will she work?
I think I have finally done it.[/quote] For yog's sake. If you've posted 5 times while I'm asleep, posting a 6th won't make me wake up.
I can't tell if your code works or not since you changed the structures again and didn't post what it now is, but it looks like you've added 3 or 4 useless pointers which are only helpful for working around bugs in your code.
[/QUOTE] It will not work, for all the reasons I gave you in my last post, which I really, really, really wish you'd read.
---------- Post updated at 11:43 AM ---------- Previous update was at 11:09 AM ----------
And you're still forgetting all your return 1's! The return 0's and error checking are useless if you don't return success when you actually have success!
Here's working code for a linked list.
Code:
#include <stdio.h>
#include <stdlib.h>
struct descr
{
int state;
struct descr *next;
};
// We pass a pointer to the head pointer for the list since we may need to
// change it.
struct descr *append_list(struct descr **head, int state) // Add new thing to the end
{
struct descr *list;
// Create new node
struct descr *n=malloc(sizeof(struct descr));
if(n == NULL) return(NULL); // Return error if malloc failed.
n->state=state;
n->next=NULL;
// Empty list? Set head and we're done.
if((*head) == NULL)
{
(*head)=n;
return(n); // return success
}
list=(*head); // set list to the first node.// We know the list must not be empty now.
// Fast-forward until we're at the last descr.
while(list->next != NULL) list=list->next;
// Set the 'next' of the last descr to the new descr.
list->next=n;
// 'head' is fine where it is, so we're all done.
return(n);
}
// Deletes all nodes set to the number 'state'.
int delete_state(struct descr **head, int state)
{
struct descr *list;
if((*head) == NULL) return(1); // Nothing to do when empty, but that's okay// If the list goes 0-> 0-> 0-> 0, we'll need to delete
// the first node over and over. After we delete, the second
// becomes the first, so we start over.
while((*head)->state == state)
{
struct descr *tmp=(*head)->next;
free(*head); // Free the first node in the list
(*head)=tmp; // Set the head pointer to the new first node
if((*head) == NULL) return(1); // If list==NULL here, the list is empty and we're done!
}
// Below here, we're no longer changing the first node, so don't have to
// worry about updating (*head).
list=(*head);
while(list->next != NULL)
{
// Keep deleting the node after the current one until we find a node
// we don't need to delete. When we delete the node after,
// the node after that becomes the new 'next', so it's a loop.
while(list->next->state == state)
{
struct descr *tmp=list->next->next; // Save the node after
free(list->next);
list->next=tmp;
// if list->next is NULL, list->next->state will CRASH!
// So when it is, quit the loop immediately!
if(list->next == NULL) break;
}
list=list->next;
if(list == NULL) break; // NULL means we hit the end of the list and must stop NOW!
}
return(0);
}
void free_list(struct descr **head)
{
while((*head) != NULL)
{
struct descr *tmp=(*head)->next;
free(*head);
(*head)=tmp;
}
}
int main(void)
{
struct descr *head=NULL; // This is the head pointer our functions change with '(*head)'
struct descr *n, *a, *b, *c, *d, *e, *f; // These will point to nodes we make.// create a list 0->1->2->0->3->0
a=append_list(&head, 0);
b=append_list(&head, 1);
c=append_list(&head, 2);
d=append_list(&head, 0);
e=append_list(&head, 3);
f=append_list(&head, 0);
e->state=4; // Update the '3' node to '4'// print each node.
for(n=head; n!=NULL; n=n->next)
printf("-> %d", n->state);
printf("\n");
// delete all nodes where state==0
delete_state(&head, 0);
// print it again.
for(n=head; n!=NULL; n=n->next)
printf("-> %d", n->state);
printf("\n");
// Beware that pointers a, d, and f are invalid now since
// their memory was freed
// Don't use f->state or anything now.
// Free the entire list. It will set head to NULL, too.
free_list(&head);
}
Last edited by Corona688; 09-30-2011 at 02:56 PM..
I didn't spam so you would answer faster I just kept updating my post so
you would see that stuff before you replied. Stuff just hit me while I tried
to make this stuff work.
Anyways I have been using all the stuff you talked about. Could you just
look at my last modification of initialize descriptor and see if it will cause
errors or not.
I know that struct descr **p changes to what I want it to be
but I just wanted to know what you thought about making a linked
list of all the descriptors. I'm worried about the lines under the text // I think I'm updating my descr_list after this line */
Code:
/* this is defined globally */
struct descr *descr_list = NULL;
/* These are defined before main */
struct descr
{
int newfd; /* Player socket */
char char_name[11]; /* Character's name */
char char_pass[25]; /* Character's password */
short int sex; /* Character's sex */
short int state; /* Maximum states allowed, 65536 */
short int create_state /* Character creation state */
struct queue *q; /* Here to queue character input */
struct descr *next /* Used to create a linked list */
struct descr *list; /* Used to define the top of the linked list */
};
int initialize_descr(int newfd, struct descr **p)
{
struct descr *d;
/* ok creating descriptor for struct descr **p */
if(!(d = malloc(sizeof(struct descr))))
{
nonfatal("malloc failure initializing descr");
return 0;
}
d->newfd = newfd;
d->state = 1;
if(!(d->q = malloc(sizeof(struct descr))))
{
nonfatal("malloc failure initializing descr queue");
d->state = 0;
return 0;
}
d->q->next = NULL;
d->next = NULL;
/* *p = d works if I use a pointer to a descr structure initialize_descr(newfd, &init) init being struct descr *init; */
*p = d;
// I think I'm updating my descr_list after this line */
if(descr_list == NULL)
{
descr_list = d;
descr_list->list = descr_list;
}
else
{
while(descr_list->next != NULL)
{
descr_list=descr_list->next;
}
descr_list->next = d;
descr_list->next->list = descr_list->list;
descr_list = descr_list->list;
}
return 1;
}
/* ok these are defined before I use the function initialize_desc they are before my main server loop that loops infinetly */
descr_list->next = NULL;
descr_list->list = descr_list;
/* then I use the function just to make sure everything works the way I want it to */
struct descr *init;
/* newfd is just an open socket */
initialize_descr(newfd, &init);
You should not keep the head pointer inside the list, no. You'll still need another head pointer to point to the head pointer -- how else will your program find it? Which makes it a bit redundant.
Try my working code and get back to me.
In case you missed it it was:
Code:
#include <stdio.h>
#include <stdlib.h>
struct descr
{
int state;
struct descr *next;
};
// We pass a pointer to the head pointer for the list since we may need to
// change it.
struct descr *append_list(struct descr **head, int state) // Add new thing to the end
{
struct descr *list;
// Create new node
struct descr *n=malloc(sizeof(struct descr));
if(n == NULL) return(NULL); // Return error if malloc failed.
n->state=state;
n->next=NULL;
// Empty list? Set head and we're done.
if((*head) == NULL)
{
(*head)=n;
return(n); // return success
}
list=(*head); // set list to the first node.
// We know the list must not be empty now.
// Fast-forward until we're at the last descr.
while(list->next != NULL) list=list->next;
// Set the 'next' of the last descr to the new descr.
list->next=n;
// 'head' is fine where it is, so we're all done.
return(n);
}
// Deletes all nodes set to the number 'state'.
int delete_state(struct descr **head, int state)
{
struct descr *list;
if((*head) == NULL) return(1); // Nothing to do when empty, but that's okay
// If the list goes 0-> 0-> 0-> 0, we'll need to delete
// the first node over and over. After we delete, the second
// becomes the first, so we start over.
while((*head)->state == state)
{
struct descr *tmp=(*head)->next;
free(*head); // Free the first node in the list
(*head)=tmp; // Set the head pointer to the new first node
if((*head) == NULL) return(1); // If list==NULL here, the list is empty and we're done!
}
// Below here, we're no longer changing the first node, so don't have to
// worry about updating (*head).
list=(*head);
while(list->next != NULL)
{
// Keep deleting the node after the current one until we find a node
// we don't need to delete. When we delete the node after,
// the node after that becomes the new 'next', so it's a loop.
while(list->next->state == state)
{
struct descr *tmp=list->next->next; // Save the node after
free(list->next);
list->next=tmp;
// if list->next is NULL, list->next->state will CRASH!
// So when it is, quit the loop immediately!
if(list->next == NULL) break;
}
list=list->next;
if(list == NULL) break; // NULL means we hit the end of the list and must stop NOW!
}
return(0);
}
void free_list(struct descr **head)
{
while((*head) != NULL)
{
struct descr *tmp=(*head)->next;
free(*head);
(*head)=tmp;
}
}
int main(void)
{
struct descr *head=NULL; // This is the head pointer our functions change with '(*head)'
struct descr *n, *a, *b, *c, *d, *e, *f; // These will point to nodes we make.
// create a list 0->1->2->0->3->0
a=append_list(&head, 0);
b=append_list(&head, 1);
c=append_list(&head, 2);
d=append_list(&head, 0);
e=append_list(&head, 3);
f=append_list(&head, 0);
e->state=4; // Update the '3' node to '4'
// print each node.
for(n=head; n!=NULL; n=n->next)
printf("-> %d", n->state);
printf("\n");
// delete all nodes where state==0
delete_state(&head, 0);
// print it again.
for(n=head; n!=NULL; n=n->next)
printf("-> %d", n->state);
printf("\n");
// Beware that pointers a, d, and f are invalid now since
// their memory was freed
// Don't use f->state or anything now.
// Free the entire list. It will set head to NULL, too.
free_list(&head);
}
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