hcreate, hdestroy, hsearch - hash table management


     #include <search.h>

     ENTRY *hsearch(ENTRY item, ACTION action));

     int hcreate(unsigned nel));

     void hdestroy(void);


     These three functions allow the user to create a hash  table
     which associates a key with any data.

     First the table must be created with the function hcreate().
     nel  is  an  estimate of the number of entries in the table.
     hcreate() may adjust this value upward to improve  the  per-
     formance  of  the resulting hash table.  The GNU implementa-
     tion of hsearch() will also enlarge the  table  if  it  gets
     nearly  full.   malloc(3)  is used to allocate space for the

     The corresponding function hdestroy() frees the memory occu-
     pied  by  the  hash  table  so  that a new table can be con-

     item is of  type  ENTRY,  which  is  a  typedef  defined  in
     <search.h> and includes these elements:

          typedef struct entry
              char *key;
              char *data;
            } ENTRY;

     key points to the zero-terminated ASCII string which is  the
     search  key.   data  points to the data associated with that
     key.  (A pointer to a type other than  character  should  be
     cast  to pointer-to-character.)  hsearch() searches the hash
     table for an item with the same key as item, and if success-
     ful  returns  a  pointer  to  it.   action  determines  what
     hsearch() does after an unsuccessful  search.   A  value  of
     ENTER  instructs it to insert the new item, while a value of
     FIND means to return NULL.


     hcreate() returns NULL if the hash table cannot be  success-
     fully installed.

     hsearch() returns NULL if  action  is  ENTER  and  there  is
     insufficient  memory  to expand the hash table, or action is
     FIND and item cannot be found in the hash table.


     SVID, except that in SysV, the hash table cannot grow.


     The implementation can manage only one hash table at a time.
     Individual hash table entries can be added, but not deleted.


     The following program inserts 24 items in to a  hash  table,
     then prints some of them.

         #include <stdio.h>
         #include <search.h>

         char *data[]={ "alpha", "bravo", "charley", "delta",
              "echo", "foxtrot", "golf", "hotel", "india", "juliette",
              "kilo", "lima", "mike", "november", "oscar", "papa",
              "quebec", "romeo", "sierra", "tango", "uniform",
              "victor", "whiskey", "x-ray", "yankee", "zulu"

         int main()
           ENTRY e, *ep;
           int i;

           /* start with small table, and let it grow */
           for (i = 0; i < 24; i++)
               e.key = data[i];
               /* data is just an integer, instead of a pointer
                  to something */
      = (char *)i;
               ep = hsearch(e, ENTER);
               /* there should be no failures */
               if(ep == NULL) {fprintf(stderr, "entry failed\n"); exit(1);}
           for (i = 22; i < 26; i++)
             /* print two entries from the table, and show that
                two are not in the table */
               e.key = data[i];
               ep = hsearch(e, FIND);
               printf("%9.9s -> %9.9s:%d\n", e.key, ep?ep->key:"NULL",
           return 0;



     bsearch(3), lsearch(3), tsearch(3),