hsearch(3C)															       hsearch(3C)

NAME

       hsearch(), hcreate(), hdestroy() - manage hash search tables

SYNOPSIS

DESCRIPTION

       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 (defined in the header file) containing two pointers: points to the comparison key, and 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  indicating  the  disposition of the entry if it cannot be found in the table.  indicates that the item should be
       inserted in the table at an appropriate point.  indicates that no entry should be made.	Unsuccessful resolution is indicated by the return
       of a NULL pointer.

       allocates  sufficient space for the table, and must be called before 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.

       destroys the search table, and can be followed by another call to

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) {

			/* 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
",
				 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 VALUE

       returns a NULL pointer if either the action is and the item could not be found or the action is and the table is full.

       returns zero if it cannot allocate sufficient space for the table.

WARNINGS

       and use to allocate space (see malloc(3C)).

       Only one hash search table can be active at any given time.

SEE ALSO

       bsearch(3C), lsearch(3C), malloc(3C), string(3C), tsearch(3C), thread_safety(5).

STANDARDS CONFORMANCE

																       hsearch(3C)