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)