hsearch(3) DG/UX 4.30 hsearch(3)
NAME
hsearch, hcreate, hdestroy - manage hash search tables
SYNOPSIS
#include <search.h>
ENTRY *hsearch (item, action)
ENTRY item;
ACTION action;
int hcreate (nel)
unsigned nel;
void hdestroy ( )
DESCRIPTION
Hsearch is a hash-table search routine generalized from
Knuth (6.4) Algorithm D. It returns a pointer into a hash
table indicating where an entry can be found.
Item is a structure of type ENTRY (defined in the <search.h>
header file) containing two pointers: item.key points to
the comparison key, and item.data points to any other data
to be associated with that key. (Pointers to types other
than character should be cast to pointer-to-character.)
Action is a member of an enumeration type ACTION indicating
what to do with the entry if it cannot be found in the
table. ENTER indicates that the item should be inserted in
the table at an appropriate point. FIND indicates that no
entry should be made. Unsuccessful resolution is indicated
by the return of a NULL pointer.
Hcreate allocates space for the table, and must be called
before hsearch is used. Nel is an estimate of the maximum
number of entries that the table will contain. This number
may be adjusted upward by the algorithm in order to obtain
certain mathematically favorable circumstances.
Hdestroy destroys the search table, and may be followed by
another call to hcreate.
NOTES
Hsearch uses open addressing with a multiplicative hash
function. However, its source code has many other options.
If you have the source code, then you can select these
options by compiling the hsearch source with the following
symbols defined to the preprocessor:
DIV Use remainder-modulo-tablesize as the hash
function instead of the multiplicative
algorithm.
Licensed material--property of copyright holder(s) Page 1
hsearch(3) DG/UX 4.30 hsearch(3)
USCR Use a user supplied comparison routine to see
if an entry is in the table. The routine
should be named hcompar and should behave like
strcmp (see string(3C)).
CHAINED Use a linked list to resolve collisions.
These are the options for CHAINED:
START Place new entries at the beginning
of the linked list (default is at
the end).
SORTUP Keep the linked list sorted by key
in ascending order.
SORTDOWN Keep the linked list sorted by key
in descending order.
There are also preprocessor flags to get debugging printout
(-DDEBUG) and to include a test driver in the calling
routine (-DDRIVER).
EXAMPLE
The following example will read in strings followed by two
numbers and store them in a hash table, discarding
duplicates. It will then read in strings, find the matching
entry in the hash table, and print it out.
#include <stdio.h>
#include <search.h>
struct info { /* this is the info stored in the table */
int age, room; /* other than the key. */
};
#define NUM_EMPL 5000 /* # of elements in search table */
main( )
{
/* space to store strings */
char string_space[NUM_EMPL*20];
/* space to store employee info */
struct info info_space[NUM_EMPL];
/* next avail space in string_space */
char *str_ptr = string_space;
/* next avail space in info_space */
struct info *info_ptr = info_space;
ENTRY item, *found_item, *hsearch( );
/* name to look for in table */
char name_to_find[30];
int i = 0;
/* create table */
Licensed material--property of copyright holder(s) Page 2
hsearch(3) DG/UX 4.30 hsearch(3)
(void) hcreate(NUM_EMPL);
while (scanf("%s%d%d", str_ptr, &info_ptr->age,
&info_ptr->room) != EOF && i++ < NUM_EMPL) {
/* put info in structure, and structure in item */
item.key = str_ptr;
item.data = (char *)info_ptr;
str_ptr += strlen(str_ptr) + 1;
info_ptr++;
/* put item into table */
(void) hsearch(item, ENTER);
}
/* access table */
item.key = name_to_find;
while (scanf("%s", item.key) != EOF) {
if ((found_item = hsearch(item, FIND)) != NULL) {
/* if item is in the table */
(void)printf("found %s, age = %d, room = %d\n",
found_item->key,
((struct info *)found_item->data)->age,
((struct info *)found_item->data)->room);
} else {
(void)printf("no such employee %s\n",
name_to_find)
}
}
}
SEE ALSO
bsearch(3C), lsearch(3C), malloc(3C), malloc(3X),
string(3C), tsearch(3C).
DIAGNOSTICS
Hsearch returns a NULL pointer if the action is FIND and the
item could not be found, or if the action is ENTER and the
table is full.
Hcreate returns zero if it cannot allocate enough space for
the table.
WARNING
Hsearch and hcreate use malloc(3C) to allocate space.
BUGS
Only one hash search table may be active at once.
Licensed material--property of copyright holder(s) Page 3