This section will document any updates applied to the project since original release:

• revision #: <description> (DATESTAMP)

In this project, we take our first opportunity to undergo a complete code re-write of node functionality, and we will also introduce the necessary functionality for doubly linked node operations.

As this is a rewrite, dln0 is not based on any of the code you have written up to this point. As such, the transition process is slightly different:

lab46:~/src/data/sll4$ make get-dln0
...

The “get-” functionality is distinct from the “upgrade-” you have been using to transition between the sll* projects. When you upgrade, your existing code is copied over, because the next project builds upon what you did previously.

But when you “get” dln0, you are getting an entirely new project skeleton- NONE of your existing code is copied over (the structure has changed enough where copying your own code would have been rather problematic).

Once you run “make get-dln0” you should have a dln0 directory that you can access and commence working on just as you have with the other project directories.

For this project, we're going to be re-implementing MOST of the previous node and list functions. There have been a few changes, namely:

1

#ifndef _NODE_H
#define _NODE_H
 
#include <stdlib.h>
#include "data.h"
 
// node struct
//
struct node {
        char         value;
        struct node *after;
        struct node *prior;
};
 
// function prototypes
//
code_t  mknode(Node **, char  );       // allocate new node containing value
code_t  cpnode(Node *,  Node **);      // duplicate node
code_t  rmnode(Node **);               // deallocate node
 
#endif

There is an addition of a “prior” node pointer, to allow connections to our previous neighbors.

The node info element has been renamed to “value”, just to make sure you understand what is going on code-wise.

You'll notice that node.h includes a file called data.h; This header will contain predominantly useful #define statements, typedefs, and support function prototypes to make our lives easier. It will see additional content added with future projects.

1

#ifndef _DATA_H
#define _DATA_H
 
// custom types (mostly for shortening typing)
//
typedef struct node            Node;   // because we deserve nice things
typedef unsigned long long int code_t; // status code data type
typedef unsigned long long int ulli;
typedef   signed long long int slli;
 
// Status codes for the doubly linked node implementation
//
#define  DLN_SUCCESS         1    // 0x01, 0001, 00000001
#define  DLN_MALLOC_FAIL     2    // 0x02, 0002, 00000010
#define  DLN_ALREADY_ALLOC   4    // 0x04, 0004, 00000100
#define  DLN_NULL            8    // 0x08, 0010, 00001000
#define  DLN_ERROR           16   // 0x10, 0020, 00010000
#define  DLN_DEFAULT_FAIL    32   // 0x20, 0040, 00100000
#define  DLN_INVALID         64   // 0x40, 0100, 01000000
#define  DLN_RESERVED_CODE   128  // 0x80, 0200, 10000000
 
// Function prototypes
//
void lscodes(code_t);
 
#endif

You'll notice the presence of a set of #define's in the data.h header file. These are intended to be used to report on various states of node status after performing various operations.

They are not exclusive- in some cases, multiple states can be applied. The intent is that you will OR together all pertinent states and return that from the function.

• DLN_SUCCESS - everything went according to plan, no errors encountered, average case
• DLN_MALLOC_FAIL - memory allocation failed (considered in error)
• DLN_ALREADY_ALLOC - memory has already been allocated (considered in error)
• DLN_NULL - result is NULL (probably in error)
• DLN_DEFAULT_FAIL - default state of unimplemented functions (default error)
• DLN_ERROR - some error occurred
• DLN_INVALID - invalid use (NULL pointer)
• DLN_RESERVED_CODE - reserved for future use (not used at present time)

For example, in the case of “DLN_MALLOC_FAIL”, there are actually a total of three states raised:

• DLN_ERROR (a problem has occurred)
• DLN_MALLOC_FAIL (a problem has occurred when using malloc())
• DLN_NULL (no memory allocated, so node cannot be anything but NULL)

ALL THREE states must be returned from the function in question should such an occurrence take place.

You'll notice these #defines map to numeric values, and particular ones at that. This is to our supreme advantage: if you understand how numbers work, you should have an easy time of working with these status codes.

In src/node/, you will find skeletons of what was previously there, ready for you to re-implement.

Figure out what is going on, the connections, and make sure you understand it.

Be sure to focus on implementing the functionality from scratch (the more you do this from scratch, vs. referencing old code, the more it will help you).

To assist you in verifying a correct implementation, a fully working implementation of the node and list libraries should resemble the following (when running the respective verify script):

Here is what you should get for node:

lab46:~/src/data/dln0$ bin/verify-node.sh 
====================================================
=    Verifying Doubly-Linked Node Functionality    =
====================================================
 [mknode] Total:  12, Matches:  12, Mismatches:   0
 [cpnode] Total:  15, Matches:  15, Mismatches:   0
 [rmnode] Total:   4, Matches:   4, Mismatches:   0
====================================================
[RESULTS] Total:  31, Matches:  31, Mismatches:   0
====================================================
lab46:~/src/data/dln0$