Path: utzoo!attcan!uunet!crdgw1!uakari.primate.wisc.edu!uflorida!mephisto!prism!prism.gatech.EDU!ce1zzes
From: ce1zzes@prism.gatech.EDU (Eric Sheppard)
Newsgroups: comp.lang.c
Subject: Define a linked list of a linked list
Message-ID: <13821@hydra.gatech.EDU>
Date: 19 Sep 90 00:19:02 GMT
Sender: ce1zzes@prism.gatech.EDU
Organization: Georgia Institute of Technology
Lines: 46

I've just given myself a crash course in C, to bring myself up to speed. My 
first project, a FORTRAN to C program conversion, was a resounding success.
The resulting program uses linked structures for dynamic data input; no more
hard-coded arrays!  Makes the new program much more efficient and flexible.
My next project is to convert another one of my old FORTRAN programs, but this
one seems a bit more difficult.

The problem: I'm not quite sure how to handle a linked list of a linked list.
Structure :  First member 4 char header, successive members 6 char data and
               1 char flag.
aaaa
bbbbbb c
bbbbbb c
 ...
bbbbbb c     Number of successive members must be variable; best way to
             implement this is with a linked list.

I will be building a file of structures of the above format, and need to
manipulate and organize them, preferably in memory; a kind of database. 
Depending on how efficiently the structures can be organized, I shouldn't have
to worry about running out of memory (small-scale database running on 
mainframe).  Since the total number of linked lists is not fixed, how can a
linked list of the above linked list be defined?

One idea:  Place the header and next-structure-pointer into the outer list, 
and the successive members into the inner list.

struct inner { 
  char data[7]; 
  char flag; 
  struct inner *next; 
  };
typedef struct inner INNR;
typedef INNR *PT_INNR;

struct outer { 
  char header[5]; 
  struct INNR;               <- not sure about this declaration. Use pointer?
  struct outer *next; 
  };
typedef struct outer OUTR;
typedef OUTR *PT_OUTR;

Are there any dangers involved with this setup?  Advice would be appreciated...

Eric, tinkerer-at-large