[SOLVED]C-Style Input Output with a linked list

Mythios (1058)
Well if anyone can point out what I'm doing wrong. Output seems fine but the input crashes on me. As it's not reading the file correctly.


1
1.000000
1
1.000000
1
1.000000
1
1.000000
1
1.000000
1
1.000000
1
1.000000



1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
 
void SaveListToFile(Node **pStart, Node **pCurrent)
{
	FILE *pFile = fopen("linkedlist.txt", "w");

	while( (*pStart)->next != NULL )
	{
		//Save To File Here
		fprintf(pFile, "%d\n", (*pStart)->age);
		fprintf(pFile, "%f\n", (*pStart)->height);
		*pStart = (*pStart)->next;
	}

	fclose(pFile);
}

void OpenListFromFile(Node **pStart, Node **pCurrent)
{
	FILE *pFile = fopen("linkedlist.txt", "r");

	if( pFile != NULL )
	{
		while( !feof(pFile) )
		{
			fscanf(pFile, "%d\n%f\n", &(*pStart)->age, &(*pStart)->height); 
			*pStart = (*pStart)->next;
		}
	}

	fclose(pFile);
}


pCurrent isn't used at the moment. Just trying to figure out what I'm doing wrong while reading the file.

Cheers,
Myth.
Last edited on
kbw (9488)
SaveListToFile is fine.

OpenListFromFile should create a new node, read the data from the file into it and add it to the front or back of the list.

You're reading data from the file into the same note each time and (re)setting the next ponter to the head node. You end up with a list with a single node that points to itself as the next node. The should cause SaveListToFile to drop into an infinite loop displaying the last entry of the file.
Mythios (1058)
Any idea on how exactly I should change it so I'm not infinite looping. As I feel that this could be done without a temporary variable.

Thanks kbw

It's reading the file like this though as well

+ pFile 0x695e1448 {_ptr=0x007934a9 "
1.111111
2
2.222222
3
3.333333
4
4.444444
5
5.555555
6
6.666666
7
7.777777

7
7.777777
ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ _ _iobuf *


So It's taking 7 and 7.77777 twice and I gather Í is for some form of non-initialized variable. Hmmm?

The saving file was wrong. Just fixed it by doing this.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
 
void SaveListToFile(Node **pStart, Node **pCurrent)
{
	FILE *pFile = fopen("linkedlist.txt", "w");

	while( *pStart != NULL )
	{
		//Save To File Here
		fprintf(pFile, "%d\n", (*pStart)->age);
		fprintf(pFile, "%f\n", (*pStart)->height);
		*pCurrent = *pStart;
		*pStart = (*pStart)->next;
	}
	fclose(pFile);
}

Was looking at the next Node pointer within the struct when I should of been looking at the struct itself
Last edited on
Mythios (1058)
It's cool just figured it out..
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
 
void OpenListFromFile(Node **pStart, Node **pCurrent)
{
	FILE *pFile = fopen("linkedlist.txt", "r");

	if( pFile != NULL )
	{
		while( !feof(pFile) )
		{
			Node *pTemp, *pTempTwo;
			pTemp = new Node;
			fscanf(pFile, "%d\n", &pTemp->age );
			fscanf(pFile, "%f\n", &pTemp->height );

			pTemp->next = NULL;
			
			// Set up link to this node
			if( *pStart == NULL )
			{ 
				*pStart = pTemp;
				*pCurrent = *pStart;
			}
			else
			{ 
				pTempTwo = *pStart;

				while ( pTempTwo->next != NULL )
				{  
					pTempTwo = pTempTwo->next;
					// Move to next link in chain
				}
				pTempTwo->next = pTemp;
			}
		}
	}
	fclose(pFile);
}


Did a wonderful job ;)
kbw (9488)
That'll do.

You could maintain a pointer to the end of the list (the last node added), and that would save you from walking down to the end each time, giving constant time insertion rather than O(n) insertion.
Topic archived. No new replies allowed.