navigating in a linked list

Hi,

I am having trouble making navigation in a linked list work.
I am tying to make it go to the first, last, next and previous record from a text file.

Do you know how to do this? could you give me a source code example?

thank you

kendals

You have to build the list from the text file first. Read the data from the file and place it in nodes. After that it's a simple matter of sending your iteration pointer through the list. Assuming it's a double linked list

Code:

---

/* Find first */
while ( iter->prev != NULL )
  iter = iter->prev;

/* Find last */
while ( iter->next != NULL )
  iter = iter->next;

/* Find next */
iter = iter->next;

/* Find previous */
iter = iter->prev;

---

A single linked list is a little more complex, to find the first you assign the iterator to the head pointer and to find the previous you will have to maintain a whisker variable. When your whisker finds the data you access the iterator and that will be the previous node.

Code:

---

/* Find first */
iter = head;

/* Find last */
while ( iter->next != NULL )
  iter = iter->next;

/* Find next */
iter = iter->next;

/* Find previous */
while ( whisker->data != key ) {
  iter = iter->next;
  whisker = iter->next;
}

---

-Prelude

How do you build the list from the text file first and Read the data from the file and place it in nodes?

could you tell me and give me an example.

thanks

kendals

Once you have the file open, just read a line and parse that line into the data for the linked list. Consider a list that has a simple string as the data member of a node:

Code:

---

char buffer[BUFSIZ];
while ( fgets ( buffer, sizeof buffer, INFILE ) != NULL ) {
  iter->next = malloc ( sizeof ( struct node ) );
  iter = iter->next;
  strncpy ( iter->data, buffer, strlen ( buffer ) );
}

---

This code should read a line from the file, then place it in a new node until it reaches the end of the file or there is an error.

-Prelude

Hi,

When i make my menu in the menu functions do i put those next and previous codes in?

I have an idea of a menu i can do can you tell me if this is ok?

do i make it like:

MENU

1) view records
2) make reports
3) exit program

From here im not sure how to make this display, like how do i put the next and previous on the screen. Do i need to have them at the bottom like a bottom navigation using gotoxy?

like this:

record displayed

------------------------------------------
(1)Next (2) Back (3) First (4) Last

Is this ok? or is there a better way?

Thanks

How about a separate menu for View Records. When the user selects that option a new menu will pop up.

Please select an option:
1) Go to the first record
2) Go to the previous record
3) Go to the next recod
4) Go to the last record

Beneath the menu would be the information for the current record so that the user knows which way to go.

Or more along the lines of your idea
Record #
-------
/* Data for the record here */

-------
Go to:
(1) First (2) Previous (3) Next (4) Last

-Prelude

thanks, i never heard of that way before, how can you do this?

I've found a switch statement to work best for a menu such as this. If the switch reads a view case then you clear the screen and write the new menu. Go into the nested case and do your processing of the new menu.

Code:

---

switch ( selection ) {
  case 1:
    clearScr();
    printViewMenu();
    /* Get Input */
    switch ( input ) {
      case 1:
        /* Work */
        break;
      case 2:
        /* Work */
        break;
    .
    .
    .

---

-Prelude

Hi,

Thanks, Im thinking of putting a help section in the menu so it will help the user, you think i should make the help file in txt and make printf dump the text on to the screen. Is that ok or you know a better way?

thanks

>Is that ok
I don't see why not

-Prelude

Hi prelude

Thanks for your help

p.s what if the text is too big scan you scroll down the page? how you do that?

In console mode it should automatically scroll. Some systems won't let you scroll back up, so you solve that problem by only printing out a few lines at a time and use getchar() to let the user read at their leisure and continue when they want.

Code:

---

while ( !end of data ) {
  Print a few lines
  printf ( "Press enter to continue\n" );
  getchar();
}

---

-Prelude