I have a simple assignment that the professor wants us to do. Basically to pull in some numbers from a text file and load into a linked list. I don't want to get to much into the details but I have a basic question.
He provided us with a function like so:
INTLIST* init_intlist( int n )
{
INTLIST *lst;
lst = (INTLIST *)malloc(sizeof(INTLIST));
lst->datum = n;
lst->next = NULL;
return lst;
}
This function is used to initialize the linked list with the first element. Then he asked us to define a function with this signature:
int insert_intlist( INTLIST *lst, int n )
So I assume he just wants us to add to the linked list so I tried this:
int insert_intlist( INTLIST *lst, int n )
{
INTLIST* lstTemp;
lstTemp = (INTLIST *)malloc(sizeof(INTLIST));
lstTemp->datum = n;
lstTemp->next = lst;
lst = lstTemp;
free(lstTemp);
}
So what my thought process was is that it creates a temporary node, assigns the data value (Datum) and assigns the next pointer to point to where the current pointer is pointing at. Then I reassign the main pointer to this newly created temp node.
That way we have for instance 2 nodes:
[New Temp Node] -> [Prev Initialized Node]
When I step through the code it looks great...
Then back in main I have just a function to print the list:
while (lst!=NULL)
{
printf("The value is:%d", lst->datum);
lst=lst->next;
}
The problem is this only seems to print one digit (namely the first digit that I am reading in from the file, which I think is the last one in the list or at least I thought it was the last one in the list).
But it should keep going through as I have 10 digits in the file. I know the code is very dirty and I will clean it up...here is my entire main function if anyone needs more info:
#include <stdio.h>
#include <stdlib.h>
#include "intlist.h"
int main(int argc, char *argv[])
{
char c; /* Character read from the file. */
FILE* ptr; /* Pointer to the file. FILE is a
structure defined in <stdio.h> */
int index=0;
//INTLIST* aList[10]; //will use later
/* Open the file - no error checking done */
ptr = fopen("1.txt","r");
/* Read one character at a time, checking
for the End of File. EOF is defined
in <stdio.h> as -1 */
if(ptr==NULL) {
printf("Error: can't open file.\n");
/* fclose(file); DON'T PASS A NULL POINTER TO fclose !! */
return 1;
}
//aList[index] = malloc(sizeof(INTLIST)); WE NEED THIS LATER ON....
INTLIST *lst=NULL;
while ((c = fgetc(ptr)) != EOF)
{
if (c != ' ')
{
//make sure it isnt a space
int i = c - '0'; //get the value from the text file
if(c=='\n')
{
// aList[index]=lst;
// index++;
// aList[index] = malloc(sizeof(INTLIST));
while (lst!=NULL)
{
printf("The value is:%d", lst->datum);
lst=lst->next;
}
free(lst);
free(aList[index]);
return 0;
//new line in the file
//create another linked list
}
if (lst==NULL)
lst = init_intlist(i);
else
insert_intlist( lst, i);
}
}
fclose(ptr);
system("PAUSE");
return 0;
}
Here is intlist.h for anyone who may need it:
#ifndef __intlist_h__
#define __intlist_h__
/* each entry in the list contains an int */
typedef struct intlist {
int datum;
struct intlist *next;
} INTLIST;
INTLIST *init_intlist( int n ); /* initializes the intlist with initial datum n */
int insert_intlist( INTLIST *lst, int n ); /* Inserts an int (n) into an intlist from the beginning*/
void list_append(INTLIST *list, void *datum); /* Inserts entry to the end of the list */
INTLIST* list_front(INTLIST *list); /*return the element at the front of the list, and remove it
from the list*/
void list_map( INTLIST *list, void (*f)(void *) ); /*Applies a function to each element of the list */
void list_delete( INTLIST *list ); /* Deletes (and frees) all entries in the list */
#endif