hsearch(3C)                    DG/UX 5.4R3.00                    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.


   Considerations for Threads Programming
                     +---------+-----------------------------+
                     |         |                      async- |
                     |function | reentrant   cancel   cancel |
                     |         |              point    safe  |
                     +---------+-----------------------------+
                     |hcreate  |     N          -        -   |
                     |hdestroy |     N          -        -   |
                     |hsearch  |     N          -        -   |
                     +---------+-----------------------------+

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



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hsearch(3C)                    DG/UX 5.4R3.00                    hsearch(3C)


       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 */

       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)
                    }



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hsearch(3C)                    DG/UX 5.4R3.00                    hsearch(3C)


                }
                return 0;
       }

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.

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

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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