BSEARCH(3C)          INTERACTIVE UNIX System          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
               The bsearch function 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 if 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 */
                    char str_space[20];   /* space to read string into */


          Rev. C Software Development Set                            Page 1

          BSEARCH(3C)          INTERACTIVE UNIX System          BSEARCH(3C)



                    .
                    .
                    .
                    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));
               }

          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.

          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.







          Rev. C Software Development Set                            Page 2