hsearch(3C)         (C Programming Language Utilities)          hsearch(3C)


   NAME
         hsearch, hcreate, hdestroy - manage hash search tables

   SYNOPSIS
         #include <search.h>

         ENTRY *hsearch (ENTRY item, ACTION action);

         int hcreate (sizet nel);

         void hdestroy (void);

   DESCRIPTION
         hsearch 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 is the function strcmp.  The comparison function used by hsearch
         is strcmp [see string(3C)].  item is a structure of type ENTRY
         (defined in the search.h header file) 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.)  action 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.

         hcreate allocates sufficient space for the table, and must be called
         before hsearch is used.  nel is an estimate 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.

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

   EXAMPLE
         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 out.

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

               struct info {           /* this is the info stored in the table */


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   hsearch(3C)         (C Programming Language Utilities)          hsearch(3C)


                     int age, room;    /* other than the key. */
               };

               #define NUMEMPL    5000    /* # of elements in search table */

               main( )
               {
                     /* space to store strings */
                     char stringspace[NUMEMPL*20];
                     /* space to store employee info */
                     struct info infospace[NUMEMPL];
                     /* next avail space in stringspace */
                     char *strptr = stringspace;
                     /* next avail space in infospace */
                     struct info *infoptr = infospace;
                     ENTRY item, *founditem;
                     /* name to look for in table */
                     char nametofind[30];
                     int i = 0;

                     /* create table */
                     (void) hcreate(NUMEMPL);
                     while (scanf("%s%d%d", strptr, &infoptr->age,
                            &infoptr->room) != EOF && i++ < NUMEMPL) {
                           /* put info in structure, and structure in item */
                           item.key = strptr;
                           item.data = (void *)infoptr;
                           strptr += strlen(strptr) + 1;
                           infoptr++;
                           /* put item into table */
                           (void) hsearch(item, ENTER);
                     }

                     /* access table */
                     item.key = nametofind;
                     while (scanf("%s", item.key) != EOF) {
                         if ((founditem = hsearch(item, FIND)) != NULL) {
                           /* if item is in the table */
                           (void)printf("found %s, age = %d, room = %d\n",
                                 founditem->key,
                                 ((struct info *)founditem->data)->age,
                                 ((struct info *)founditem->data)->room);
                         } else {
                           (void)printf("no such employee %s\n",
                                 nametofind)
                         }
                     }
                     return 0;
               }




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   hsearch(3C)         (C Programming Language Utilities)          hsearch(3C)


   SEE ALSO
         bsearch(3C), lsearch(3C), malloc(3C), malloc(3X), string(3C),
         tsearch(3C).

   DIAGNOSTICS
         hsearch 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.

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

   NOTES
         hsearch and hcreate use malloc(3C) to allocate space.

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






































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