need help with file I/O and double linked-list

This is a discussion on need help with file I/O and double linked-list within the C++ Programming forums, part of the General Programming Boards category; I'm trying to set up a double linked-list, that is a linked-list within a linked-list. the structure looks like this: ...

  1. #1
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    Feb 2003
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    need help with file I/O and double linked-list

    I'm trying to set up a double linked-list, that is a linked-list within a linked-list. the structure looks like this:

    Code:
    struct Dat
    {
          int acc;
          int spd;
          Dat *nextdat;
          Dat *prevdat;
    };
    
    struct Node
    {
          char name [64];
          char pass [16];
          int avg_acc;
          int avg_spd;
    
          Dat *dat,
                *dat_h,
                *dat_t;
    
          Node *next,     
    	*prev;
    };
    
    Node *node, //current node
             *list_h, //head
             *list_t; //tail
    my problem is saving the entire structure to a file, and then being able to open it up later. Saving the initial linked-list isn't a problem. But the pointers within the first linked-list which create the second linked-list may be a problem. Also, I can't come up with a successful way to get the data from the file and back into a linked list. My initial idea was to set up an initial node, open the file, save the data from the first node to the initial node, then create a new node, save the next data to that node, and so on until the eof is encountered. The problem is getting the second linked-list into the file, and back out. Here is my attempt at saving the file:

    Code:
    void LList::SaveToFile ()
    {
          int i;
    
          ofstream data ("data.dat");
    
          node = list_h;
    
          while (node)
          {
    	data.write((char*)node, sizeof(Node));  			node = node->next;   //does this write the internal linked-list as well? 
          }
    
          data.close ();
    }
    Can anyone help me with the syntax for this file operation or point me somewhere that describes this type of problem?
    Last edited by jamie; 02-20-2003 at 07:09 PM.

  2. #2
    Registered User matheo917's Avatar
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    279
    theoretically speaking you're on the right track...

    when it comes to saving linked list to a file, a "rule of thumb" is to only save the "data" portion of a linked list (of each node) into a file -----> not the entire node nor pointers associated with it, b/c the next time you run your program those pointers will have an address of a memory location that is not associated with your program, that's why it's called RAM (random access memory)

    the same pertains to reading in your values....like you stated you create a new node and read in DATA from the file and insert it into each data member of a particular node....


    anyways..........when it comes to having a linked list inside of a linked list (that is a node having a pointer to a node of completely different type) i would recommend creating a seperate file and storing DATA of each node of that linked list into that second DIFFERENT file..........

    after all, there are other ways of doing this as well, but i think this one might be one of the easiest...


    hope that helps

    ...............
    matheo917

  3. #3
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    This helped alot. Thank you sooo much. I was trying to save the entire node into the file, without really even thinking about memory allocation, etc... Thanks again for the help.

  4. #4
    Registered User matheo917's Avatar
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    glad I could help

    ......................
    matheo917

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