bsearch(3C)             LIBRARY FUNCTIONS             bsearch(3C)



NAME
     bsearch - binary search a sorted table

SYNOPSIS
     #include <stdlib.h>

     void *bsearch (const void *key,  const  void  *base,  sizet
     nel,
     sizet size, int (*compar)(const void *, const void *));

DESCRIPTION
     bsearch is a binary search routine  generalized  from  Knuth
     (6.2.1)  Algorithm B.  It returns a pointer into a table (an
     array) indicating where a datum  may  be  found  or  a  null
     pointer  if  the  datum  cannot be found.  The table must be
     previously sorted in increasing order according  to  a  com-
     parison  function  pointed  to  by  compar.  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.  size is the number of bytes in  each
     element.   The  function pointed to by compar 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 0 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  program  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 <stdlib.h>
          #include <string.h>

          struct node {            /* these are stored in the table */
               char *string;
               int length;
          };
          static struct node table[] =  /* table to be searched */
          {
               { "asparagus", 10 },
               { "beans", 6 },
               { "tomato", 7 },
               { "watermelon", 11 },
          };




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bsearch(3C)             LIBRARY FUNCTIONS             bsearch(3C)



          main()
          {
               struct node *nodeptr, node;
               /* routine to compare 2 nodes */
               static int nodecompare(const void *, const void *);
               char strspace[20];   /* space to read string into */

               node.string = strspace;
               while (scanf("%20s", node.string) != EOF) {
                    nodeptr = bsearch( &node,
                            table, sizeof(table)/sizeof(struct node),
                            sizeof(struct node), nodecompare);
                    if (nodeptr != NULL) {
                         (void) printf("string = %20s, length = %d\n",
                              nodeptr->string, nodeptr->length);
                    } else {
                         (void)printf("not found: %20s\n", node.string);
                    }
               }
               return(0);
          }

          /* routine to compare two nodes based on an  */
          /* alphabetical ordering of the string field */
          static int
          nodecompare(const void *node1, const void *node2)
          {
               return (strcmp(
                         ((const struct node *)node1)->string,
                         ((const 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.

     The comparison function need  not  compare  every  byte,  so
     arbitrary  data may be contained in the elements in addition
     to the values being compared.

     If the number of elements in the table is less than the size
     reserved for the table, nel should be the lower number.

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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