bsearch(3C) — sys5



BSEARCH(3C)     DOMAIN/IX Reference Manual (SYS5)     BSEARCH(3C)



NAME
     bsearch - binary search a sorted table

USAGE
     #include <search.h>

     char *bsearch ((char *) key, (char *) base, nel, sizeof
     (*key), compar)
     unsigned nel;
     int (*compar)( );

DESCRIPTION
     Bsearch is a binary search routine generalized from Knuth
     (6.2.1) Algorithm B.  It returns a pointer into a table
     indicating where a datum may be found.  The table must have
     been sorted previously, in increasing order according to the
     comparison function that you have provided.  Key points to
     the datum to be sought in the table.  Base points to the
     element at the base of the table.  Nel is the number of ele-
     ments in the table.  Compar is the name of the comparison
     function, which is called with two arguments that point to
     the elements being compared.  The comparison function must
     return an integer less than, equal to, or greater than zero
     according to whether the first argument is to be considered
     less than, equal to, or greater than the second.

EXAMPLE
     The example below searches a table that contains pointers to
     items consisting of a string and its length.  The table is
     ordered alphabetically on the string in the item pointed to
     by each entry.

     This code fragment reads in strings and either finds the
     corresponding item and prints out the string and its length,
     or prints an error message.

          #include <stdio.h>
          #include <search.h>

          #define   TABSIZE   1000

          struct item {            /* these are stored in the table */
               char *string;
               int length;
          };
          struct item table[TABSIZE];   /* table to be searched */
               .
               .
               .
          {
               struct item *item_ptr, item;
               int item_compare( );  /* routine to compare 2 items */



Printed 5/10/85                                         BSEARCH-1



BSEARCH(3C)     DOMAIN/IX Reference Manual (SYS5)     BSEARCH(3C)



               char str_space[20];   /* space to read string into */
               .
               .
               .
               item.string = str_space;
               while (scanf("%s", item.string) != EOF) {
                    item_ptr = (struct item *)bsearch((char *)(&item),
                            (char *)table, TABSIZE,
                            sizeof(struct item), item_compare);
                    if (item_ptr != NULL) {
                         (void)printf("string = %20s, length = %d\n",
                              item_ptr->string, item_ptr->length);
                    } else {
                         (void)printf("not found: %s\n", item.string);
                    }
               }
          }
          /*
               This routine compares two items based on an
               alphabetical ordering of the string field.
          */
          int
          item_compare(item1, item2)
          struct item *item1, *item2;
          {
               return strcmp(item1->string, item2->string);
          }

NOTES
     The pointers to the key and the element at the base of the
     table should be of type pointer-to-element, and cast to type
     pointer-to-character.

     The comparison function need not compare every byte, so
     arbitrary data can be contained in the elements, along with
     the values being compared.

     Although declared as type pointer-to-character, the value
     returned should be cast into type pointer-to-element.

DIAGNOSTICS
     A NULL pointer is returned if the key cannot be found in the
     table.

RELATED INFORMATION
     hsearch(3C), lsearch(3C), qsort(3C), tsearch(3C)









BSEARCH-2                                         Printed 5/10/85

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