hsearch(3C)          COMPATIBILITY 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 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 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)          COMPATIBILITY FUNCTIONS          hsearch(3C)



          struct info {       /* this is the info stored in table */
               int age, room; /* other than the key */
          };

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

          main( )
          {
               /* space to store strings */














































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hsearch(3C)          COMPATIBILITY FUNCTIONS          hsearch(3C)



               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)          COMPATIBILITY 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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