bs

Algorithms for Image Processing and Computer Vision Source Code

@c ----------------------------------------------------------------------
@node bsearch, misc
@heading @code{bsearch}
@subheading Syntax

@example
#include <stdlib.h>

void *bsearch (const void *key, const void *base, size_t num, 
  size_t size, int (*ptf)(const void *ckey, const void *celem));
@end example

@subheading Description

Given an array of values, perform a binary search on the values looking
for value that "matches" the given key.  A match is determined by
calling the provided function @var{ptf} and passing it the key as
@var{ckey} and a pointer to one of the elements of the array as
@var{celem}.  This function must return a negative number if the key is
closer than the element to the beginning of the array, positive if
it is closer to the end, and zero if the element matches the key.

The array begins at address @var{base} and contains @var{num} elements,
each of size @var{size}. 

@subheading Return Value

Returns a pointer to the element that matches the key, else @var{NULL}.

@subheading Example

@example
typedef struct @{
  int a, b;
@} q;

int compare(void *key, void *elem)
@{
  return *(int *)key - ((q *)elem)->a;
@}

q qlist[100];

@dots{}
q *match = bsearch(4, qlist, 100, sizeof(q), compare);
printf("4->%d=n", match->b);
@dots{}

@end example