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?

Quote:

Originally Posted by cisco_leon

How do I read one line at a time until the EOF

I prefer to think of it as, "while successfully reading the intended data".
http://www.daniweb.com/techtalkforum...155265-18.html

Quote:

Originally Posted by cisco_leon

The catch is, I must not use an array!

That would be a reasonable assumption considering the intent is to implement a linked list.

Quote:

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?

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

Sure. However, you will either need to have written the pointers (or space they take up anyway) to disk also when you have created the file, or you need to have a seperate structure which just contains the useful information. If the latter, your linked list will end up looking something like:

Code:

struct node { struct node *next, *prev; struct data d; };

Then you read into the 'data' structure directly from disk.

Code:

fread( &node->d, sizeof( node->d ), 1, fp );

You follow these steps:

Code:

while not done make a new node read into the node if no error link node to list

Quzah.

Quote:

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.

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.

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.

Quote:

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.

Quote:

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.

Quote:

and all the other f-ing functions

:)

What strikes me as odd is that the OP has insisted on no arrays, but here you go...

Code:

char line[BUFSIZ];

Code:

char lastName[20]; char firstName[12];

...arrays.

All those arrays should be char*, which I guess you could then allocate 20*sizeof(char) if you wish to accomplish a similar effect.

Quote:

Originally Posted by jafet

What strikes me as odd is that the OP has insisted on no arrays, but here you go...

Code:

char line[BUFSIZ];

Code:

char lastName[20]; char firstName[12];

...arrays.

I interpreted the assignment as, "Reading a TextFile into a Linked List". That is, using a linked list of structures rather than an array of structures.

If you think instead the intent is to completely avoid an array of any kind, including C-strings, then offer some coding help in that direction.