Saving and Loading Linked Lists With File i/o

I am in desperate need of help here. I have been trying for weeks to get this program to work, and its no go. My program seems rather simple. Read in user info as a linked list, save it to a file, and then be able to choose one of those entries( Like a log in function) Now, Saving is easy. It saves fine this way...

outfile << UserList->user.Fname;

now, next, after all of the names and info have been stored in the binary file, I am supposed to be able to load it back into the program, 1 entry at a time, and choose an entry so I can put more info into that single entry. I am totally lost at this point, and have tried a huge amount of different ways to complete this part of my assignment. I even tried using a buffer and strcmp to search for partial matches. I would ask the teacher, but we ahve a sub for another 2 months who doesn't know the difference between a monitor and a toaster oven.

any help would be GREATLY appreciated.

>doesn't know the difference between a monitor and a toaster oven.
This describes most programming teachers.

This sounds like a pretty straightforward assignment, read data from a file into a linked list and find a user input key to search for so that the data at the node can be updated. Perhaps you could be a bit more specific in what the problem you are having is?

-Prelude

The error is simple. I don't know how to write the function that will read the linked list back into the program from the file.

The same way you would create a linked list from user input except you read the input from a file.

Code:

---

while ( in.good() ) {
  iter->next = new node;
  iter = iter->next;
  in>>iter->data;
  iter->next = NULL;
}

---

-Prelude

is "iter" a new list to load the info, or a previously entered list?

It's a new list, you have to rebuild the links when you load the data from the file.

-Prelude

here is the relevant code from my program, I am just gonna post it here now because I do not have access from home.
I'' try your suggestion, looks promising.

Code:

---

void Save(Users* &head)
{
        Users *savelist;
       
        savelist=head;
        int i=0;
        for(savelist=head;savelist;savelist=savelist=savelist->next)
        {
                //cout << savelist->Fname<<endl;
                //cout << savelist->Sname<<endl;
                i++;
        //        getch();
        }
        /*FILE *fp;
                if ((fp =fopen("D:\\Profiles.dat","r+b")) == NULL)
                        {
                        fp =fopen("D:\\Profiles.dat","w+b");
                // error
                        //tprintf("Creating File, retry to create user");
                        getch();
                        }
               
        savelist=head;
        while (savelist!=NULL)
        {
                cout <<"saving" <<endl;
                fwrite(&savelist->Fname,sizeof(&savelist),1,fp);
                savelist=savelist->next;
        }
        fclose(fp);*/
        savelist=head;
        ofstream outfile;
        outfile.open("Profiles.dat",ios::out| ios::app |ios::binary);
        //outfile <<head<<"\n";
                //outfile<<"Begin" <<"\n";
        do
        {
                outfile <<savelist->user.Fname <<"\n";
                outfile <<savelist->user.Sname <<"\n";
                outfile <<savelist->user.SepID <<"\n";
                outfile <<savelist->user.UserID <<"\n";
               
               
               
                savelist=savelist->next;
        }
        while(savelist!=NULL);

        outfile << "END";
        outfile.close();
        cout << "Save succesful";

 
}
void Login(int i,Users* &head)
{
        int profileID;
        clrscr();
        cout <<"Enter your student ID(if you have not created a profile with your user ID, you will need to return to the main menu)"<<endl;
        cin>>profileID;
        char ch ='\0';
        int length;
  char * buffer;
        i=0;
        Users *newrec;//=head;
        int endloop=1;
        ifstream readfile;
        readfile.open("Profiles.dat",ios::in |ios::binary);
        readfile.seekg((profileID-1)*sizeof(newrec),ios::beg);
        readfile.read((char *) &newrec,sizeof(Users));
        readfile >> newrec->user.Fname;
        cout <<newrec->user.Fname;
cout <<"done"<<endl;
        getch();

        /*readfile.seekg(ios::beg);
        static char reader[10];
        readfile.read(reader,endloop);
        //cout <<reader<<endl;
        do
        {
                //cout << "hello"<<endl;
        //        getch();
                //endloop++;
        readfile.read(reader,endloop);
        if(reader[10]=' ')
        {

//        cout <<reader<<endl;
//        getch();
        }
        }while (endloop != 5);
       
*/
        readfile.close();
        cout << "Load succesful";
       
 
getch();

               
}

---

Quote:

---

Originally posted by Prelude
The same way you would create a linked list from user input except you read the input from a file.

Code:

---

while ( in.good() ) {
  iter->next = new node;
  iter = iter->next;
  in>>iter->data;
  iter->next = NULL;
}

---

-Prelude

---

Crash error, Nothing specific.

What the h---. I'm bored at work. No compiler to make sure this works though.

Code:

---

#include <iostream.h>

struct node
{
  int num;
  node * next;
}

int main()
{
  //declare a list
  node * head = NULL;
  node * curr;
  int i;
//add new node to end of list each time.
for(i = 0; i < 3; i++)
{
  curr = head;
  //declare a new node to add to list
  node *newNode = new node;
  //initialize members of new node
  newNode->num = i * i;
  newNode->next = NULL;

  if(head == NULL)//this is first node in list
  {
      head = newNode;
    }
    else
  {
      //find end of list
      while(curr->next != NULL)
      {
          curr = curr->next;
      }
        //and add new node there
      curr->next = newNode;
  }
}

//write list data to file top to bottom
ofstream fout("listData.txt");
curr = head;
while(curr != NULL)
{
  fout << curr->num << endl;
  curr = curr->next;
}

fout.close();

//now read it back into a new list
ifstream fin("listData.txt")
node * newHead = NULL;
while(!fin.eof())
{
  curr = newHead;
  //declare a new node to hold file data
  node * newNode = new node;
  //read in file data one node's worth at a time
  fin >> newNode->num;
  newNode->next = NULL;
 
  //and add to end new list
  if(newHead == NULL)
  newHead = newNode;
  else
  {
    while(curr->next != NULL)
    {
        curr = curr->next;
      }
      curr->next = newNode;
  }
}

fin.close();

//display new list
curr = newHead;
while(curr)
{
  cout << curr->num << endl;
}

//delete memory from the lists
curr = newHead;
while(curr)
{
  while(curr->next != NULL)
  {
      curr = curr->next;
    }
    delete curr;
    curr = newHead;
}

curr = head;
while(curr)
{
  while(curr->next != NULL)
  {
    curr = curr->next;
  }
  delete curr;
  curr = head;
}

return 0;
}

---