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The C Users' Group Library 1994 August
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list.doc
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/*
HEADER: CUG308;
TITLE: documentation for generic linked list module;
DATE: 5/6/90;
VERSION: 2.01;
FILENAME: LIST.DOC;
SEE-ALSO: LIST.H, LIST.C;
AUTHOR: Michael Kelly
254 Gold Street, Boston Ma. 02127;
COPYRIGHT: May be used freely if authorship is acknowledged;
*/
- 2 -
*** CONTENTS ***
OVERVIEW --------------------------------- PAGE 3
WARNINGS --------------------------------- PAGE 3
REQUIREMENTS ------------------------- PAGE 3
COMMENTS --------------------------------- PAGE 4
NOTE --------------------------------- PAGE 4
EXAMPLE DECLARATION --------------------- PAGE 5
EXTERNAL LIST FUNCTION PROTOTYPES ------ PAGE 5
EXTERNAL LIST FUNCTION DESCRIPTIONS ------ PAGE 6 to PAGE 8
LIST MEMBER FUNCTION CALLS ----------------- PAGE 9
LIST MEMBER FUNCTION PROTOTYPES ---------- PAGE 9
LIST MEMBER FUNCTION DESCRIPTIONS ------ PAGE 10 to PAGE 25
- 3 -
*** OVERVIEW ***
The List module provides generic doubly linked list management
functions that can operate on data blocks of non-uniform size. The List
routines are accessed through List structure member function pointers to
allow changes in the implementation while minimizing client module
source changes.
Two external functions are also provided, initlist(), to initialize
a List variable, and compact_list_table(), to free unused list table
memory and move the remaining table entries to contiguous slots. The
latter is provided for applications that may use a large number of lists
initially, and delete most of them during program execution.
One example that comes to mind would be a "merge sort" with each
list containing a sorted "run". If this were developed on say, an MsDos
machine, using a version of the List code modified to include a
disk-swapping scheme, it may be possible to simply recompile the
application with the unmodified List code on a system that supports
virtual memory.
*** WARNINGS ***
The function listsfree() has been removed. See COMMENTS.
An integer member variable, "id" was added to the List structure.
See COMMENTS. See LIST.H.
The enumeration definition for the Lerror (List error indicator)
variable has been updated. See LIST.H.
*** REQUIREMENTS ***
Code written for prior versions will require minor modifications to
work with Version 2.0. See COMMENTS.
You MUST initialize your program List variables with the initlist()
function before calling any member List functions or a hung program will
be the most likely result.
If you have a problem, it may concern your C compiler, see
"requirements" note in LIST.C concerning dereferencing of function
pointers.
- 4 -
*** COMMENTS ***
In Versions prior to 2.0, static list tables were used, limiting
the number of available lists, no matter how much memory was available
in the system. Since the number of possible active lists is no longer
static, the function listsfree() has been removed.
Also, intermediary functions were used to pass a hidden list
pointer to the function that actually operated on the list. This was
done as a kind of experiment in simulating the C++ "this" pointer.
Version 2.0 uses a dynamically allocated array of list pointers to
make better use of system memory. An integer member variable, "id" was
added to the List structure. This variable is set in the initlist()
function and must be passed as the first parameter in list member
function calls. In Version 2.0 this "id" is used as an index into the
List table but it could also be used as a "handle" to implement a
disk-swapping scheme on systems without virtual memory.
Although this approach is not as much fun as the kludge in prior
versions (the "include" files have been eliminated), the code is now
smaller, faster and more flexible. Some global search and replace
should be able to update old client code.
*** NOTE ***
The destroy() member function in Versions prior to 2.0 set the List
structure variable to all zeros. If the program subsequently made a
call through a destroyed List, it would use a NULL function pointer to
unhappy results. In Version 2.0, after freeing the memory owned by the
List, the List member variable "id" is set to -1 and the function
pointers left intact. When List member functions are called they check
the List id, and if it is not valid, set "lerror" and return 0 or NULL.
This makes the module more robust, reducing system "lockup" during
debugging in unprotected environments.
- 5 -
*** EXAMPLE DECLARATION ***
#include "list.h"
List *mylist1, mylist2;
*** EXTERNAL LIST FUNCTION PROTOTYPES ***
extern int initlist(List *newlist, int (*cmpfunc)());
extern int compact_list_table(void);
- 6 -
*** EXTERNAL LIST FUNCTION DESCRIPTIONS ***
extern int initlist(List *newlist, int (*cmpfunc)());
ACTION:
Initializes the List member variables and functions.
Stores the address of the List variable.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
newlist is a pointer to a variable of type List
cmpfunc is a pointer to a function to compare two List items
that returns a signed integer that is:
== 0 if item1 == item2
< 0 if item1 < item2
> 0 if item1 > item2
WARNINGS:
A List variable MUST be initialized with this function
before any member functions for that List are called.
( see example on next page )
- 7 -
*** EXTERNAL LIST FUNCTION DESCRIPTIONS ***
*** initlist() EXAMPLE ***
#include <stdio.h>
#include <string.h>
#include "list.h"
List *mylist1, mylist2;
char list_ptr_use[] = "using List pointer variable";
char list_var_use[] = "using List variable";
main()
{
int status;
mylist1 = (List *) malloc(sizeof(List));
if(! mylist1) {
printf("\nmalloc() Failure!\n");
exit(EXIT_FAILURE);
}
if(! initlist(mylist1, strcmp)) {
printf("\nInitialization failed\n");
exit(EXIT_FAILURE);
}
/*
* need "&" to point to static List structure
*/
if(! initlist(&mylist2, strcmp)) {
printf("\nInitialization failed\n");
exit(EXIT_FAILURE);
}
status = mylist1->add(mylist1->id, list_ptr_use,
strlen(list_ptr_use) + 1, CURRENT);
status += mylist2.add(mylist2.id, list_var_use,
strlen(list_var_use) + 1, CURRENT);
if(status != 2) {
printf("\nError adding items to Lists\n");
exit(EXIT_FAILURE);
}
...
}
- 8 -
*** EXTERNAL LIST FUNCTION DESCRIPTIONS ***
extern int compact_list_table(void);
ACTION:
Moves active List pointers to lowest position in List
table and frees unused table memory.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
None.
EXAMPLE:
/*
* mylist is a dynamic array of List *
* purge 3 of every 4 Lists (for some purpose or other)
* and reclaim the memory
*/
for(i = 0;i < TOTAL_LISTS;i++)
if(i % 4)
mylist[i]->destroy(mylist[i]->id);
if(compact_list_table()) {
List **tmplist;
tmplist = realloc(mylist, (TOTAL_LISTS / 4));
if(tmplist)
mylist = tmplist;
else {
printf("\nList compaction error\n");
exit(EXIT_FAILURE);
}
}
...
- 9 -
*** LIST MEMBER FUNCTION CALLS ***
These are the List member functions that are bound to the List on
which they operate by the initlist() function. They are called as a
member of the List variable ( e.g. mylist.next(mylist.id) ). All the
examples in this section will assume a variable of type List named
mylist.
*** LIST MEMBER FUNCTION PROTOTYPES ***
/*
* int add(int id, void *item, size_t itemsize, enum Place place);
* int chgcompare(int id, int (int id, *newcompare)());
* int cmpitem(int id, void *item1);
* int delete(int id);
* int destroy(int id);
* int find(int id, void *item1);
* int first(int id);
* int getitem(int id, void *itembuf);
* void *getptr(int id);
* size_t getsize(int id);
* int last(int id);
* int next(int id);
* int prev(int id);
* int remitem(int id, void *itembuf);
* int replitem(int id, void *newitem, size_t newsize);
* int sort(int id);
*/
- 10 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int add(int id, void *item, size_t itemsize, enum Place place);
ACTION:
Adds an item to a particular List.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
item is a void pointer to the item to store
itemsize is an unsigned integer that is the size in bytes
of the item ( must be > 0 )
place is one of FIRST, LAST or CURRENT (defined in list.h)
position in the List
FIRST stores the item at the head of the List
LAST stores the item at the tail end of the List
CURRENT stores the item immediately after the "current"
item in the List
in all three cases the stored item becomes the "current" item
EXAMPLE:
main()
{
FILE *fp;
List mylist;
struct record {
char name[40];
char phone[20];
}rec;
if(initlist(&mylist,strcmp)) {
fp = fopen("phone.dat","rb");
while(!feof(fp))
if(fread(&rec,sizeof rec,1,fp) == 1)
if(!mylist.add(mylist.id, &rec, sizeof rec, LAST))
break;
}
- 11 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int chgcompare(int id, int (*newcompare)());
ACTION:
Binds a different compare function to the List variable.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
newcompare() follows the description given for cmpfunc()
in initlist()
COMMENTS:
You may have called initlist() with a function that compares two
structures using the "last_name" field as the key, but now you wish to
sort the List by telephone number area code. chgcompare() allows
the substitution of another compare function.
EXAMPLE:
if(! mylist.chgcompare(mylist.id, cmpnums)) {
printf("\nError changing compare function\n");
exit(EXIT_FAILURE);
}
...
- 12 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int cmpitem(int id, void *item1);
ACTION:
Compares item1 to the "current" item in the List.
RETURNS:
The integer result of a comparison between item1 and
the "current" item, using the compare function that
was passed to initlist() or chgcompare().
ARGUMENTS:
id is the List member variable whose value is
assigned by initlist()
item1 is a void pointer to the item to compare.
EXAMPLE: if(mylist.cmpitem(mylist.id, &rec1) == 0)
mylist.replitem(mylist.id, &rec1, sizeof rec1);
- 13 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int delete(int id);
ACTION:
Deletes the "current" item from the List.
Sets the "current" pointer to the first item in the List.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
EXAMPLE:
if(! mylist.delete(mylist.id))
if(lerror == EMPTY_LIST)
return;
- 14 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int destroy(int id);
ACTION:
Returns dynamic memory allocated to the List.
Removes table entry for the List.
Sets id member variable to an "invalid" value.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
EXAMPLE:
do {
printf("\n%s",mylist.getptr(mylist.id))
}
while(mylist.next(mylist.id));
mylist.destroy(mylist.id);
return;
COMMENTS:
Instead of setting the List member functions to NULL, V. 2.0
sets the id variable to -1 so that calls from Lists that have
been destroyed set lerror to an error code and return NULL or 0.
- 15 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int find(int id, void *item1);
ACTION:
Performs a linear search of the List for an item that
compares equal to item1, using the comparison function
that was passed to initlist() or chgcompare().
RETURNS:
0 if no match is found
1 if a match is found and the matching item in the List
is now the "current" item
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
item1 is a void pointer to the item to match
EXAMPLE:
if(! mylist.find(mylist.id, &employee_rec))
mylist.add(mylist.id, &employee_rec,
sizeof employee_rec, LAST);
- 16 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int first(int id);
ACTION:
Makes the first item in List the "current" item.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
EXAMPLE:
if(! mylist.first(mylist.id)) /* quit if List empty */
exit(0);
else
do_something();
- 17 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int getitem(int id, void *itembuf);
ACTION:
Copies the "current" item in the List to itembuf.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
itembuf is a void pointer to the memory destination
of the copy operation
WARNINGS:
Make sure itembuf is large enough to hold the "current"
item. You can get the size in bytes of the "current"
item with the getsize() member function.
EXAMPLE:
mylist.first(mylist.id);
if(mylist.entries > 0)
do {
mylist.getitem(mylist.id, &record);
fwrite(&record,sizeof record, 1, fp);
}
while(mylist.next(mylist.id));
- 18 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
void *getptr(int id);
ACTION:
Returns the address of the "current" item in the List.
RETURNS:
on success:
void pointer to the "current" item in the List
on failure:
NULL and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
WARNINGS:
Included for efficiency. Beware of corrupting the
memory block if you write data to this address that
is larger than that allocated for the "current" item.
You can get the size in bytes of the "current" item in
the List with the getsize() member function.
EXAMPLE:
if(! mylist.first(mylist.id)) { /* List is empty */
fclose(fp);
exit(0);
}
do {
fwrite(mylist.getptr(mylist.id),
mylist.getsize(mylist.id), 1, fp);
}
while(mylist.next(mylist.id));
fclose(fp);
- 19 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
size_t getsize(int id);
ACTION:
Returns the size in bytes of the "current" item in the List.
RETURNS:
on success:
an unsigned integer equal to the size of the current
item in bytes ( must be > 0 )
on failure:
0 and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
EXAMPLE:
if(mylist.getsize(mylist.id) > buffer_size) {
void *tmpbuf;
buffer_size = mylist.getsize(mylist.id);
tmpbuf = realloc(buffer, buffer_size);
if(! tmpbuf) {
printf("realloc failure!");
exit(EXIT_FAILURE);
}
buffer = tmpbuf;
}
mylist.remitem(mylist.id, buffer);
- 20 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int last(int id);
ACTION:
Makes the last item in the List the "current" item.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
EXAMPLE:
/* show sorted List in rev order */
mylist.sort(mylist.id);
if(mylist.last(mylist.id))
do {
printf("\n%s",mylist.getptr(mylist.id))
}
while(mylist.prev(mylist.id));
- 21 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int next(int id);
ACTION:
Makes the next item in the List the "current" item.
RETURNS:
0 if next link is NULL ( does not move pointer ) or
sets lerror to error code if id is invalid (see list.h)
1 on success
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
EXAMPLE:
if(mylist.first(mylist.id)) {
int i;
i = 1;
while(mylist.next(mylist.id))
++i;
if(i != mylist.entries) {
printf("List Module Error : Big Bug!");
exit(EXIT_FAILURE);
}
}
else
list_is_empty();
- 22 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int prev(int id);
ACTION:
Makes the previous item in the List the "current" item.
RETURNS:
0 if previous link is NULL ( does not move pointer ) or
sets lerror to error code if id is invalid (see list.h)
1 on success
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
EXAMPLE:
mylist.last(mylist.id);
while((mylist.cmpitem(mylist.id, &newrecord) < 0)
&& mylist.prev(mylist.id))
; /* empty loop -- insert in List in sorted order */
mylist.add(mylist.id, &newrecord,sizeof newrecord, CURRENT);
- 23 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int remitem(int id, void *itembuf);
ACTION:
Copies the "current" item in the List to itembuf,
then removes the "current" item from the List.
Makes the first item in the List the "current" item.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
WARNINGS:
Make sure itembuf is large enough to hold the "current"
item. You can get the size in bytes of the "current"
item with the getsize() member function.
EXAMPLE:
if(sizeof buffer >= mylist.getsize(mylist.id))
mylist.remitem(mylist.id, buffer);
- 24 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int replitem(int id, void *newitem, size_t newsize);
ACTION:
Replaces the "current" item in the List with the item
pointed to by newitem. If the replacement is successful
the old "current" item is deleted from the List.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
newitem is a void pointer to the item that is to take
the place of the "current" item in the List
newsize is the size in bytes of the new item
EXAMPLE:
if(mylist.find(mylist.id, &newrecord))
mylist.replitem(mylist.id, &newrecord,
sizeof newrecord);
- 25 -
*** LIST MEMBER FUNCTION DESCRIPTIONS ***
int sort(int id);
ACTION:
Sorts the List in ascending order according to the
comparison function installed with the initlist()
or chgcompare() functions, using the host qsort()
function. The first item in the sorted List becomes
the "current" item.
RETURNS:
1 on success
0 on failure and sets lerror to an error code (see list.h)
ARGUMENTS:
id is the List member variable whose value is assigned
by initlist()
EXAMPLE:
/* display in reverse order */
if(mylist.sort(mylist.id)) {
mylist.last(mylist.id);
do {
printf("\n%s",mylist.getptr(mylist.id))
}
while(mylist.prev(mylist.id));
}
