Thread: WIP Borland C Doubly linked list

Originally Posted by Salem

OK, but you're still reading from a file opened for writing

> fread(p, sizeof(item), 1, in);
> scanf("%s",&p->name);
I thought you just read the information from the file, why are you also reading from the user, and overwriting what you read from the file?

According your notice i changed file mode to rb
so now it looks like this

Code:

in=fopen("data.txt","rb");
    do { p=(item *)new item;
    fread(p, sizeof(item), 1, in);

I still can't understand

1.So I open file
2.And read 1 structure sizeof(item) from file
3. But what to do next?

If im not mistaken struct item consist of data and pointers? so what to do with them? or they wasnt saved with data?
I decided to use scanf. Is this right choice? Or the procedure shouold be different?
I have too many questions but I can't find answers anythere

Code:

  in=fopen("data.txt","rb");
    do { p=(item *)new item;
    fread(p, sizeof(item), 1, in);
    scanf("%s",&p->name);
    scanf("%d",&p->prc);
    scanf("%d",&p->col);
    p->prev=pr;
  if(pr != NULL)
    pr->next=p;
  else
    head=p;
    pr=p;
}
while (!feof(in));
    tail=p;
    tail->next=NULL;
}

So I need to rewrite the add function to append data from user as well as from file?
what does the list mean in your code?

btw is this single linked list?
Oh

This code dose not produce any errors. It creates list and fills is, then saves to file and try to load. I tryed to printf the content loaded from file. Works fine. But is it podssible to do such a way

read one structure from file and use it to fill new structure? till the end of file
Also I wounder does my clear memory function work?

Code:

#include <stdio.h>
#include <conio.h>
#include <alloc.h>
#include <string.h>
struct item
{char name[20];int prc; int col;
  struct item *prev;
  struct item *next;
};
void build(void);
void view(struct item *);
void load(void);
struct item *head,*tail;
main(){
clrscr();
build();
view(head);
getch();
clrscr();
printf("\nfrom file");
load();
view(head);
getch();
}
void build(void)
{item *p,*pr;
  pr=NULL;

    do { p=(item *)malloc(sizeof(item));
    clrscr();
    printf("Name : ");
    scanf("%s",&p->name);
    printf("\nPrc : ");
    scanf("%d",&p->prc);
    printf("\nCol: ");
    scanf("%d",&p->col);
    p->prev=pr;
  if(pr != NULL)
    pr->next=p;
  else
    head=p;
    pr=p;
    printf("Esc");
}
while (getch()!=27);
    tail=p;
    tail->next=NULL;
}
void load(void)
{
item *p,*pr;
FILE *in;
while(p!=NULL)
{
p=p->next; //Clears memory
free(p);
}
in=fopen("data.txt","rb");
do{p=(item *)malloc(sizeof(item));
  fread(p,sizeof(item),1,in);
 p->prev=pr;
  if(pr != NULL)
    pr->next=p;
  else
    head=p;
    pr=p;
    printf("Esc");
}
while (!feof(in));
    tail=p;
    tail->next=NULL;
}

void view(item *p)
{
     int i=1;
     FILE *in;
     clrscr();
     in=fopen("data.txt","wb");
     if( in != NULL )
     {
         while (p != NULL)
         {
               printf("\n %-2d   %-15s\t%3d\t%3d",i,p->name, p->prc, p->col);

               if(!fwrite(p, sizeof(item),1,in))
               {
                   perror("fwrite");
                   getchar();
                   fclose(in);
                   return;
               }
               i++;
               p = p->next;
         }
         fclose(in);
     }
     else
     {
         printf("Error: File cannot be created/opened\n");
         printf("Press any key to continue...\n");
         getchar();
         return;
     }
}

Or can you help me to change variables in your append and load functions to mine which i used in my code? Such as item p next prev etc.
Please

Can load from file function be realized such a way. If im not misstaken I read one structure from file to memory. Then if I want to prin it I can use something like this

printf("\n %d %s\t%d\t%d",i,p->name, p->prc, p->col)

so p->name, p->prc, p->col mean that I can read them from memory. But can I use them to create new item of the list? If yes how to get them an assign to new thread

I though it can be realized such a way bout its just fought. Can somebody answer my questions?

Code:

void load(void)
{item *p, *ni, *pr;
FILE *in;
p = head;
while(p!=NULL)
{
    item *pTemp;
    pTemp=p->next;
    free(p);
    p = pTemp;
}
in=fopen("data.txt","rb");
do{
  ni=(item *)malloc(sizeof(item));
  fread(p,sizeof(item),1,in);
  p->name=ni->name;
  p->prc=ni->prc;
  p->col=ni->col;
  ni->prev=pr;
  if(pr != NULL)
    pr->next=p;
  else
    head=ni;
    pr=ni;
    printf("Esc");
}
while (!feof(in));
    tail=ni;
    tail->next=NULL;
}