Thread: Reading a TextFile into a Linked List

Hi guys,
Need some help reading a space delimited text file into a linked list.

The text file looks like this:
012452 John Smith 23.56
891756 Joe Bloe 24.94
268174 Sample Smith 18.56
718756 Terry Totts 27.86
261786 James Packer 25.98

Each record is one line in the above file. I need to read in 4 fields from the above:
int empNo; char firstname; char lastame; double rate;

How do I read one line at a time until the EOF, while at the same time capturing each of the four fields per record.

The catch is, I must not use an array!

Please let me know if anyone can help me start this code.

Cheers!

Well, first_name and last_name have to be arrays. Or pointers. And if that array catch does not encompass pointers than you could use fgets and memory allocated with malloc or similar. Does it seem like the teacher would want you to read in the data character by character and do all the conversions yourself? If so, are there any guarantee's other than four fields being space delimited that you could think of to make it easier for yourself?

Originally Posted by Tonto

Well, first_name and last_name have to be arrays. Or pointers. And if that array catch does not encompass pointers than you could use fgets and memory allocated with malloc or similar. Does it seem like the teacher would want you to read in the data character by character and do all the conversions yourself? If so, are there any guarantee's other than four fields being space delimited that you could think of to make it easier for yourself?

Hi,
Sorry there doesn't seem to be any other guarantees in the spec I've been given.

I guess, the first question for me to find an answer to is:
1. Is it possible to load records from such a text file, straight into a linked list, without the use of arrays? if so, what would the pseudo code look like?

Originally Posted by Dave_Sinkula

Have a structure that represents a single record. Read data into the structure. Add the structure to the list.

Hi Dave,
1. Have a structure that represents a single record.

Code:

struct charRecord
{
   char letter;
   int empNum;
   char lastName;
   char firstName;
   double hourRate;
   struct charRecord *next;
};

typedef struct charRecord charNode;

2. Read data into the structure.
Here is where I get stuck. Specifically the "read data" part.

3. Add the structure to the list.
If it was an array of strings, I can do it, but avoding arrays I don't know how.

Originally Posted by quzah

For starters, your record is wrong, unless everyone you know only has a single letter for their first and last name. Once you fix that, go read up on the file chapter of your book, or read up on fopen, fread, fwrite, fgets, fscanf, fclose, and all the other f-ing functions.


Quzah.

Ok thanks will do. Before I go on, is this correct data structure?

Code:

struct charRecord
{
   int empno;
   char lname[];
   char fname[];
   double rate;
   struct charRecord *next;
};

typedef struct charRecord employee

Please let me know.

Originally Posted by Dave_Sinkula

Only because I think you'll do it wrong and I'm just trying to skip to the chase with your linked list, I'll give you this little early Christams present with the file reading.

Code:

#include<stdio.h>

struct record
{
   char   letter;
   int    empNum;
   char   lastName[20];
   char   firstName[12];
   double hourRate;
};

int main(void)
{
   static const char filename[] = "file.txt";
   FILE *file = fopen(filename, "r");
   if ( file != NULL )
   {
      char line[BUFSIZ];
      struct record record;
      while ( fgets(line, sizeof line, file) != NULL &&
              sscanf(line, "%d %11s %19s %lf", 
                     &record.empNum, record.firstName, 
                     record.lastName, &record.hourRate) == 4 )
      {
#ifndef NDEBUG /* while debugging */
         printf("%10d %-20s %-12s %g\n", 
                record.empNum, record.lastName, 
                record.firstName, record.hourRate);
#else /* real code */
         /* add 'record' to linked list */
#endif
      }
      fclose(file);
   }
   else
   {
      perror(filename);
   }
   return 0;
}

/* my output
     12452 Smith                John         23.56
    891756 Bloe                 Joe          24.94
    268174 Smith                Sample       18.56
    718756 Totts                Terry        27.86
    261786 Packer               James        25.98
*/

So basically, fgets & sscanf.

Thanks Dave! Appreciate, will give that a go.