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Jul 4th, 2009

Reading link list in files..

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Hello.. How can I read a link list from a file without reading a garbage node? I don't know much about how file works..
This is my code fragment:

c Syntax (Toggle Plain Text)
for(p = A; flag != 1;)
	 {
		  *p = (LIST) malloc(sizeof(celltype));
		  if((fread(*p, sizeof(celltype), 1, fp)) == 0)
				flag = 1;
		  p = &(*p)->next;
	 }
	 *p = NULL;
for(p = A; flag != 1;)
	 {
		  *p = (LIST) malloc(sizeof(celltype));
		  if((fread(*p, sizeof(celltype), 1, fp)) == 0)
				flag = 1;
		  p = &(*p)->next;
	 }
	 *p = NULL;

please help

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Whilliam

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Jul 4th, 2009

Re: Reading link list in files..

- read into temporary memory
- if successful, allocate a node, copy the data and append to the list.

Salem

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Jul 4th, 2009

Re: Reading link list in files..

Click to Expand / Collapse Quote originally posted by Salem ...

- read into temporary memory
- if successful, allocate a node, copy the data and append to the list.

I don't think that will ignore the garbage node..
should I just put a sentinel value in my structure when I wright files instead?

Whilliam

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Re: Reading link list in files..

C Syntax (Toggle Plain Text)
LIST *list = NULL;
while ( fread( &temp, sizeof temp, 1, fp ) == 1 ) {
  LIST *node = makeNewNode( &temp ); // allocate and copy
  list = append( list, node ); // append
}
LIST *list = NULL;
while ( fread( &temp, sizeof temp, 1, fp ) == 1 ) {
  LIST *node = makeNewNode( &temp ); // allocate and copy
  list = append( list, node ); // append
}

Where is the junk node?
If the file is empty, then the list at the end is NULL (an empty list).

Salem

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Re: Reading link list in files..

Click to Expand / Collapse Quote originally posted by Salem ...

C Syntax (Toggle Plain Text)
LIST *list = NULL;
while ( fread( &temp, sizeof temp, 1, fp ) == 1 ) {
  LIST *node = makeNewNode( &temp ); // allocate and copy
  list = append( list, node ); // append
}
LIST *list = NULL; while ( fread( &temp, sizeof temp, 1, fp ) == 1 ) { LIST *node = makeNewNode( &temp ); // allocate and copy list = append( list, node ); // append }
Where is the junk node?
If the file is empty, then the list at the end is NULL (an empty list).

it reads an extra loop which contains garbage values..

this is my "wright" code fragment:

c Syntax (Toggle Plain Text)
for(p = L; p != NULL; p=p->next)
	fwrite(p, sizeof(celltype), 1, fp);
for(p = L; p != NULL; p=p->next)
	fwrite(p, sizeof(celltype), 1, fp);

am I doing this right?

Whilliam

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Jul 4th, 2009

Re: Reading link list in files..

> p = A;
It seems you start off with a junk node to begin with.

Salem

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Re: Reading link list in files..

Click to Expand / Collapse Quote originally posted by Salem ...

> p = A;
It seems you start off with a junk node to begin with.

The node containing garbage value appears at the last..

Last edited by Whilliam; Jul 4th, 2009 at 8:54 am.

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Jul 5th, 2009

Re: Reading link list in files..

Click to Expand / Collapse Quote originally posted by Whilliam ...

The node containing garbage value appears at the last..

So if your concern is just the last but one node that is if you say that the node whose node->link is your junk node and you don't want to read it then you can just do this :

c Syntax (Toggle Plain Text)
for(p = L; p->next != NULL; p=p->next)
for(p = L; p->next != NULL; p=p->next)

So that you stop writing just before the last node.

Last edited by csurfer; Jul 5th, 2009 at 12:04 am.

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Re: Reading link list in files..

Click to Expand / Collapse Quote originally posted by Whilliam ...

The node containing garbage value appears at the last..

It would appear at the last, in case the way you append is something that you have written to actually add the node to the beginning rather than the end. Just make sure that is not the case.

SNIP

Last edited by happygeek; Jul 6th, 2009 at 10:18 am. Reason: fake sig snipped, please read the rules regarding signatures

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