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BSEARCH(3P)		   POSIX Programmer's Manual		   BSEARCH(3P)

       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       bsearch — binary search a sorted table

       #include <stdlib.h>

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

       The functionality described on this reference page is aligned with  the
       ISO C  standard.	 Any  conflict between the requirements described here
       and the ISO C standard is unintentional. This  volume  of  POSIX.1‐2008
       defers to the ISO C standard.

       The  bsearch()  function shall search an array of nel objects, the ini‐
       tial element of which is pointed	 to  by	 base,	for  an	 element  that
       matches	the object pointed to by key.  The size of each element in the
       array is specified by width.  If the nel argument has the  value	 zero,
       the comparison function pointed to by compar shall not be called and no
       match shall be found.

       The comparison function pointed to by compar shall be called  with  two
       arguments that point to the key object and to an array element, in that

       The application shall ensure that the comparison function pointed to by
       compar does not alter the contents of the array. The implementation may
       reorder elements of the array between calls to the comparison function,
       but shall not alter the contents of any individual element.

       The  implementation  shall  ensure  that the first argument is always a
       pointer to the key.

       When the same objects (consisting of width bytes, irrespective of their
       current	positions  in the array) are passed more than once to the com‐
       parison function, the results shall be  consistent  with	 one  another.
       That  is,  the  same  object shall always compare the same way with the

       The application shall ensure that the function returns an integer  less
       than,  equal  to,  or  greater  than 0 if the key object is considered,
       respectively, to be less than, to match, or  to	be  greater  than  the
       array  element. The application shall ensure that the array consists of
       all the elements that compare less than, all the elements that  compare
       equal  to,  and	all  the  elements  that  compare greater than the key
       object, in that order.

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

       No errors are defined.

       The following sections are informative.

       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.

       The code fragment below reads in strings and either  finds  the	corre‐
       sponding	 node  and  prints out the string and its length, or prints an
       error message.

	   #include <stdio.h>
	   #include <stdlib.h>
	   #include <string.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;
	       /* Routine to compare 2 nodes. */
	       int node_compare(const void *, const void *);
	       while (scanf("%ms", &node.string) != EOF) {
		   node_ptr = (struct node *)bsearch((void *)(&node),
			  (void *)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.
	   node_compare(const void *node1, const void *node2)
	       return strcoll(((const struct node *)node1)->string,
		   ((const struct node *)node2)->string);

       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‐

       In  practice,  the  array is usually sorted according to the comparison

       The requirement that the second argument (hereafter referred to	as  p)
       to  the	comparison  function  is  a pointer to an element of the array
       implies that for every call all of the following expressions  are  non-

	   ((char *)p − (char *(base) % width == 0
	   (char *)p >= (char *)base
	   (char *)p < (char *)base + nel * width


       hcreate(), lsearch(), qsort(), tdelete()

       The Base Definitions volume of POSIX.1‐2008, <stdlib.h>

       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the	referee document. The original Standard can be obtained online
       at .

       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,	 see  https://www.ker‐ .

IEEE/The Open Group		     2013			   BSEARCH(3P)

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