HSEARCH(3C) DOMAIN/IX Reference Manual (SYS5) HSEARCH(3C)
NAME
hsearch, hcreate, hdestroy - manage hash search tables
USAGE
#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 that indicates the location at which an entry can be
found. Item is a structure of type ENTRY (defined in the
<search.h> header file) that contains 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
that indicates the disposition of the entry if it isn't
found in the table.
ENTRY indicates that the item should be inserted in the
table at an appropriate point. FIND indicates that no entry
should be made. A NULL pointer indicates that no action was
possible.
Hcreate allocates sufficient space for the table; it 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, if neces-
sary.
Hdestroy destroys the search table; it may be followed by
another call to hcreate.
EXAMPLE
The following example will read in strings followed by two
numbers and store them in a hash table, discarding dupli-
cates. It will then read in strings and 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 */
Printed 5/10/85 HSEARCH-1
HSEARCH(3C) DOMAIN/IX Reference Manual (SYS5) HSEARCH(3C)
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 */
(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)
}
}
}
NOTES
Hsearch and hcreate use malloc(3C) to allocate space.
HSEARCH-2 Printed 5/10/85
HSEARCH(3C) DOMAIN/IX Reference Manual (SYS5) HSEARCH(3C)
Only one hash search table may be active at any given time.
Hsearch uses open addressing with a multiplicative hash
function.
DIAGNOSTICS
Hsearch returns a NULL pointer if either the action is FIND
and the item could not be found or the action is ENTER and
the table is full. Hcreate returns zero if it cannot allo-
cate sufficient space for the table.
RELATED INFORMATION
bsearch(3C), lsearch(3C), malloc(3C), malloc(3X),
string(3C), tsearch(3C)
Printed 5/10/85 HSEARCH-3