hsearch(3C)            UNIX System V(C Development Set)             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 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 table */
                  int age, room;    /* other than the key */
            };

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


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hsearch(3C)            UNIX System V(C Development Set)             hsearch(3C)


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



















































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hsearch(3C)            UNIX System V(C Development Set)             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)            UNIX System V(C Development Set)             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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