HCREATE(3) BSD Library Functions Manual HCREATE(3)

NAME
     hhccrreeaattee, hhddeessttrrooyy, hhsseeaarrcchh - manage hash search table

LLIIBBRRAARRYY
     Standard C Library (libc, -lc)

SYNOPSIS
     ##iinncclluuddee <>

     int
     hhccrreeaattee(sizet nel);

     void
     hhddeessttrrooyy(void);

     ENTRY *
     hhsseeaarrcchh(ENTRY item, ACTION action);

DESCRIPTION
     The hhccrreeaattee(), hhddeessttrrooyy(), and hhsseeaarrcchh() functions manage hash search
     tables.

     The hhccrreeaattee() function allocates sufficient space for the table, and the
     application should ensure it is called before hhsseeaarrcchh() is used.  The nel
     argument is an estimate of the maximum number of entries that the table
     should contain.  This number may be adjusted upward by the algorithm in
     order to obtain certain mathematically favorable circumstances.

     The hhddeessttrrooyy() function disposes of the search table, and may be followed
     by another call to hhccrreeaattee().  After the call to hhddeessttrrooyy(), the data can
     no longer be considered accessible.  The hhddeessttrrooyy() function calls
     free(3) for each comparison key in the search table but not the data item
     associated with the key.

     The hhsseeaarrcchh() function is a hash-table search routine.  It returns a
     pointer into a hash table indicating the location at which an entry can
     be found.  The item argument is a structure of type ENTRY (defined in the
      header) containing two pointers: item.key points to the com-
     parison key (a char *), and item.data (a void *) points to any other data
     to be associated with that key.  The comparison function used by
     hhsseeaarrcchh() is strcmp(3).  The action argument is a member of an enumera-
     tion type ACTION 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.  FIND indicates that no entry should
     be made.  Unsuccessful resolution is indicated by the return of a NULL
     pointer.

     The comparison key (passed to hhsseeaarrcchh() as item.key) must be allocated
     using malloc(3) if action is ENTER and hhddeessttrrooyy() is called.

RETURN VALUES
     The hhccrreeaattee() function returns 0 if it cannot allocate sufficient space
     for the table; otherwise, it returns non-zero.

     The hhddeessttrrooyy() function does not return a value.

     The hhsseeaarrcchh() function 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.

EERRRROORRSS
     The hhccrreeaattee() and hhsseeaarrcchh() functions may fail if:

     [ENOMEM]           Insufficient storage space is available.

EEXXAAMMPPLLEESS
     The following example reads in strings followed by two numbers and stores
     them in a hash table, discarding duplicates.  It then reads in strings
     and finds the matching entry in the hash table and prints it out.

     #include 
     #include 
     #include 
     #include 

     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. */

     int
     main(void)
     {
             char str[BUFSIZ]; /* Space to read string */
             struct info infospace[NUMEMPL]; /* Space to store employee info. */
             struct info *infoptr = infospace; /* Next space in infospace. */
             ENTRY item;
             ENTRY *founditem; /* Name to look for in table. */
             char nametofind[30];
             int i = 0;

             /* Create table; no error checking is performed. */
             (void) hcreate(NUMEMPL);

             while (scanf("%s%d%d", str, &infoptr->age,
                 &infoptr->room) != EOF && i++ < NUMEMPL) {
                     /* Put information in structure, and structure in item. */
                     item.key = strdup(str);
                     item.data = infoptr;
                     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);
             }
             hdestroy();
             return 0;
     }

SEE ALSO
     bsearch(3), lsearch(3), malloc(3), strcmp(3), tsearch(3)

STANDARDS     The hhccrreeaattee(), hhddeessttrrooyy(), and hhsseeaarrcchh() functions conform to X/Open
     Portability Guide Issue 4, Version 2 (``XPG4.2'').

HISTORY     The hhccrreeaattee(), hhddeessttrrooyy(), and hhsseeaarrcchh() functions first appeared in AT&T
     System V UNIX.

BUGS
     The interface permits the use of only one hash table at a time.

BSD                               May 8, 2001                              BSD