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)
Check Out this Related Man Page
HCREATE(3) BSD Library Functions Manual HCREATE(3)NAME
hcreate, hdestroy, hsearch -- manage hash search table
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <search.h>
int
hcreate(size_t nel);
void
hdestroy(void);
ENTRY *
hsearch(ENTRY item, ACTION action);
DESCRIPTION
The hcreate(), hdestroy(), and hsearch() functions manage hash search tables.
The hcreate() function allocates sufficient space for the table, and the application should ensure it is called before hsearch() is used.
The nel argument is an estimate of the maximum number of entries that the table should contain. This number may be adjusted upward by the
algorithm in order to obtain certain mathematically favorable circumstances.
The hdestroy() function disposes of the search table, and may be followed by another call to hcreate(). After the call to hdestroy(), the
data can no longer be considered accessible. The hdestroy() function calls free(3) for each comparison key in the search table but not the
data item associated with the key.
The hsearch() function is a hash-table search routine. It returns a pointer into a hash table indicating the location at which an entry can
be found. 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 (a char *), and item.data (a void *) points to any other data to be associated with that key. The comparison function used by
hsearch() is strcmp(3). The action argument is a member of an enumeration type ACTION 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. FIND indicates that no entry
should be made. Unsuccessful resolution is indicated by the return of a NULL pointer.
The comparison key (passed to hsearch() as item.key) must be allocated using malloc(3) if action is ENTER and hdestroy() is called.
RETURN VALUES
The hcreate() function returns 0 if it cannot allocate sufficient space for the table; otherwise, it returns non-zero.
The hdestroy() function does not return a value.
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 ta-
ble is full.
ERRORS
The hcreate() and hsearch() functions may fail if:
[ENOMEM] Insufficient storage space is available.
EXAMPLES
The following example reads in strings followed by two numbers and stores them in a hash table, discarding duplicates. It then reads in
strings and finds the matching entry in the hash table and prints it out.
#include <stdio.h>
#include <search.h>
#include <string.h>
#include <stdlib.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. */
int
main(void)
{
char str[BUFSIZ]; /* Space to read string */
struct info info_space[NUM_EMPL]; /* Space to store employee info. */
struct info *info_ptr = info_space; /* Next space in info_space. */
ENTRY item;
ENTRY *found_item; /* Name to look for in table. */
char name_to_find[30];
int i = 0;
/* Create table; no error checking is performed. */
(void) hcreate(NUM_EMPL);
while (scanf("%s%d%d", str, &info_ptr->age,
&info_ptr->room) != EOF && i++ < NUM_EMPL) {
/* Put information in structure, and structure in item. */
item.key = strdup(str);
item.data = info_ptr;
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);
}
hdestroy();
return 0;
}
SEE ALSO bsearch(3), lsearch(3), malloc(3), strcmp(3), tsearch(3)STANDARDS
The hcreate(), hdestroy(), and hsearch() functions conform to X/Open Portability Guide Issue 4, Version 2 (``XPG4.2'').
HISTORY
The hcreate(), hdestroy(), and hsearch() functions first appeared in AT&T System V UNIX.
BUGS
The interface permits the use of only one hash table at a time.
BSD May 8, 2001 BSD