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hsearch(3C)							   hsearch(3C)

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

       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 enu‐
       meration	 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 ta‐
       ble 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

       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

	      #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;

			/* 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\n",
				 ((struct info *)found_item->data)->age,
				 ((struct info *)found_item->data)->room);
			   } else {
				(void)printf("no such employee %s\n",

       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.

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

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

       bsearch(3C),    lsearch(3C),   malloc(3C),   string(3C),	  tsearch(3C),


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