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HSEARCH(3C)							   HSEARCH(3C)

       hsearch, hcreate, hdestroy - manage hash search tables

       #include <search.h>

       ENTRY *hsearch(ENTRY item, ACTION action);

       int hcreate(size_t mekments);

       void hdestroy(void);

       The  hsearch() function is a hash-table search routine generalized from
       Knuth (6.4) Algorithm D. It returns a pointer into a hash  table	 indi‐
       cating  the  location  at  which	 an entry can be found. The comparison
       function used by hsearch() is strcmp() (see string(3C)). The item argu‐
       ment  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.	Unsuc‐
       cessful 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  cer‐
       tain mathematically favorable circumstances.

       The  hdestroy() function destroys the search table, and may be followed
       by another call to hcreate().

       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.

       The hcreate() function returns 0 if it cannot allocate sufficient space
       for the table.

       The  hsearch()  and   hcreate()	functions  use	malloc(3C) to allocate

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

       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;
				 /* 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",
		 return 0;

       See attributes(5) for descriptions of the following attributes:

       │Interface Stability │ Standard	      │
       │MT-Level	    │ Safe	      │

       bsearch(3C), lsearch(3C),  malloc(3C),  string(3C),  tsearch(3C),  mal‐
       loc(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.

				 Dec 29, 1996			   HSEARCH(3C)

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