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  BSEARCH(3C)     (C Programming Language Utilities)    BSEARCH(3C)



  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
       provided 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


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  BSEARCH(3C)     (C Programming Language Utilities)    BSEARCH(3C)



            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 */
                 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));
            }


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  BSEARCH(3C)     (C Programming Language Utilities)    BSEARCH(3C)



  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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