BSEARCH(3C-SysV)    RISC/os Reference Manual     BSEARCH(3C-SysV)



NAME
     bsearch - binary search a sorted table

SYNOPSIS
     #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 be
     previously sorted in increasing order according to a pro-
     vided comparison function.  key points to a datum instance
     to be sought in the table.  base points to the element at
     the base of the table.  nel is the number of elements 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 function must return an integer less
     than, equal to, or greater than zero as accordingly the
     first argument is to be considered less than, equal to, or
     greater than the second.

EXAMPLE
     The example below searches a table containing pointers to
     nodes consisting of a string and its length.  The table is
     ordered alphabetically on the string in the node pointed to
     by each entry.

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

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

          #define   TABSIZE   1000

          struct node {            /* these are stored in the table */
               char *string;
               int length;
          };
          struct node table[TABSIZE];   /* table to be searched */
               .
               .
               .
          {
               struct node *node_ptr, node;
               int node_compare( );  /* routine to compare 2 nodes */



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BSEARCH(3C-SysV)    RISC/os Reference Manual     BSEARCH(3C-SysV)



               char str_space[20];   /* space to read string into */
               .
               .
               .
               node.string = str_space;
               while (scanf("%s", node.string) != EOF) {
                    node_ptr = (struct node *)bsearch((char *)(&node),
                            (char *)table, TABSIZE,
                            sizeof(struct node), node_compare);
                    if (node_ptr != NULL) {
                         (void)printf("string = %20s, length = %d\n",
                              node_ptr->string, node_ptr->length);
                    } else {
                         (void)printf("not found: %s\n", node.string);
                    }
               }
          }
          /*
               This routine compares two nodes based on an
               alphabetical ordering of the string field.
          */
          int
          node_compare(node1, node2)
          char *node1, *node2;
          {
               return (strcmp(
                         ((struct node *)node1)->string,
                         ((struct node *)node2)->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 may be contained in the elements in addition
     to the values being compared.
     Although bsearch is declared as type pointer-to-character,
     the value returned should be cast into type pointer-to-
     element.

SEE ALSO
     hsearch(3C), lsearch(3C), qsort(3C), tsearch(3C).

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








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