HP-UX Reference (11i v2 07/12) - 3 Library Functions A-M (vol 6)

h
hsearch(3C) hsearch(3C)
NAME
hsearch(), hcreate( ), hdestroy( ) - manage hash search tables
SYNOPSIS
#include <search.h>
ENTRY *hsearch(ENTRY item, ACTION action);
int hcreate(size_t nel);
void hdestroy(void);
DESCRIPTION
hsearch() 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. Only pointers are copied, so the
calling routine must store the data (the value of the "key" must be unique). item is a structure of type
ENTRY (defined in the <
search.h> header file) containing two pointers: item.key points to the com-
parison 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 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.
hcreate() allocates sufficient 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 can be adjusted
upward by the algorithm in order to obtain certain mathematically favorable circumstances.
hdestroy() destroys the search table, and can be followed by another call to hcreate() .
EXAMPLE
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>
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 */
(void) hcreate(NUM_EMPL);
while (scanf("%s%d%d", str_ptr, &info_ptr->age,
&info_ptr->room) != EOF && i++ < NUM_EMPL) {
HP-UX 11i Version 2: December 2007 Update − 1 − Hewlett-Packard Company 627