hsearch(3) Library Functions Manual hsearch(3)Name
hsearch, hcreate, hdestroy - manage hash search tables
Syntax
#include <search.h>
ENTRY *hsearch (item, action)
ENTRY item;
ACTION action;
int hcreate (nel)
unsigned nel;
void hdestroy ( )
Description
The subroutine is a hash-table search routine generalized from Knuth (6.4) Algorithm D. It returns a pointer into a hash table indicating
the location at which an entry can be found. The 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.) The action is a member of an enumeration type ACTION indicating the disposi-
tion of 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.
The subroutine allocates sufficient space for the table, and must be called before is used. The 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.
The subroutine destroys the search table, and may be followed by another call to
Restrictions
Only one hash search table may be active at any given time.
Diagnostics
The subroutine 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.
The subroutine returns zero if it cannot allocate sufficient space for the table.
See Alsobsearch(3), lsearch(3), string(3), tsearch(3)hsearch(3)
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hsearch(3C) Standard C Library Functions hsearch(3C)NAME
hsearch, hcreate, hdestroy - manage hash search tables
SYNOPSIS
#include <search.h>
ENTRY *hsearch(ENTRY item, ACTION action);
int hcreate(size_t mekments);
void hdestroy(void);
DESCRIPTION
The hsearch() function is a hash-table search routine generalized from Knuth (6.4) Algorithm D. It returns a pointer into a hash table
indicating the location at which an entry can be found. The comparison function used by hsearch() is strcmp() (see string(3C)). The item
argument is a structure of type ENTRY (defined in the <search.h> header) 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 void should be cast to pointer-to-
void.) The action argument is a member of an enumeration type ACTION (defined in <search.h>) indicating the disposition of 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. Given a duplicate of
an existing item, the new item is not entered and hsearch() returns a pointer to the existing item. FIND indicates that no entry should be
made. Unsuccessful resolution is indicated by the return of a null pointer.
The hcreate() function allocates sufficient space for the table, and must be called before hsearch() is used. The nel argument is an esti-
mate 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.
The hdestroy() function destroys the search table, and may be followed by another call to hcreate().
RETURN VALUES
The hsearch() function 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.
The hcreate() function returns 0 if it cannot allocate sufficient space for the table.
USAGE
The hsearch() and hcreate() functions use malloc(3C) to allocate space.
Only one hash search table may be active at any given time.
EXAMPLES
Example 1: Example to read in strings.
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 and find the matching entry in the hash table and print it.
#include <stdio.h>
#include <search.h>
#include <string.h>
#include <stdlib.h>
struct info { /* this is the info stored in 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;
/* 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 = (void *)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
",
found_item->key,
((struct info *)found_item->data)->age,
((struct info *)found_item->data)->room);
} else {
(void)printf("no such employee %s
",
name_to_find)
}
}
return 0;
}
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
|MT-Level |Safe |
+-----------------------------+-----------------------------+
SEE ALSO bsearch(3C), lsearch(3C), malloc(3C), string(3C), tsearch(3C), malloc(3MALLOC), attributes(5), standards(5)
The Art of Computer Programming, Volume 3, Sorting and Searching by Donald E. Knuth, published by Addison-Wesley Publishing Company, 1973.
SunOS 5.10 29 Dec 1996 hsearch(3C)