hsearch(3C)             LIBRARY FUNCTIONS             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 can-
     not 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 dupli-
     cates.  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>




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hsearch(3C)             LIBRARY FUNCTIONS             hsearch(3C)



          struct info {       /* this is the info stored in the table */
               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)             LIBRARY FUNCTIONS             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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