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BSEARCH(3C)							   BSEARCH(3C)

       bsearch - binary search a sorted table

       #include <stdlib.h>

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

       The  bsearch()  function	 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 comparison function pointed to by compar.

       The  key argument points to a datum instance to be sought in the table.
       The base argument points to the element at the base of the table.   The
       nel argument is the number of elements in the table.  The size argument
       is the number of bytes in each element.

       The comparison function pointed to by compar is called with  two	 argu‐
       ments  that  point  to  the key object and to an array element, in that
       order. The function must return an integer  less	 than,	equal  to,  or
       greater	than  0	 if  the key object is considered, respectively, to be
       less than, equal to, or greater than the array element.

       The bsearch() function returns a pointer to a matching  member  of  the
       array,  or a null pointer if no match is found.	If two or more members
       compare equal, which member is returned is unspecified.

       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  com‐

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

       The bsearch() function safely  allows  concurrent  access  by  multiple
       threads to disjoint data, such as overlapping subtrees or tables.

       Example 1 Examples for searching a table containing pointers to nodes.

       The  example  below  searches a table containing pointers to nodes con‐
       sisting 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 },

	     struct node *node_ptr, node;
	     /* routine to compare 2 nodes */
	     static int node_compare(const void *, const void *);
	     char str_space[20];   /* space to read string into */

	     node.string = str_space;
	     while (scanf("%20s", node.string) != EOF) {
		 node_ptr = bsearch( &node,
		     table, sizeof(table)/sizeof(struct node),
		     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: %20s\n", node.string);

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

       See attributes(5) for descriptions of the following attributes:

       │Interface Stability │ Standard	      │
       │MT-Level	    │ MT-Safe	      │

       hsearch(3C), lsearch(3C), qsort(3C), tsearch(3C), attributes(5),	 stan‐

				  Dec 6, 2004			   BSEARCH(3C)

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