hsearch(3C)                                                     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 was 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 (type char*), and item.data
     (void*) 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() turns a pointer to the existing
     item. FIND indicates that no entry should be made. Unsuccessful reso-
     lution is indicated by the return of a null pointer.

     hcreate() allocates sufficient storage for the table, and must be
     called before hsearch(). nel is an estimate of the maximum possible
     number of entries that the table will contain. This number may be
     adjusted upward by the algorithm in order to obtain certain mathemati-
     cally favorable circumstances.

     hdestroy() destroys the search table. It may be followed by another
     call to hcreate().

     The function fails if:

     ENOMEM    Insufficient storage space is available.














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hsearch(3C)                                                     hsearch(3C)

EXAMPLES
     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 */

     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"


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hsearch(3C)                                                     hsearch(3C)

                           founditem->key,
                           ((struct info *)founditem->data)->age,
                           ((struct info *)founditem->data)->room);
               } else {
                   (void)printf("no such employee %s\n"
                           nametofind)
               }
           }
           return 0;
     }

RESULT
     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.

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




























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