Use bsearch function to do binary search

Syntax

C bsearch function has the following syntax.

Header

C bsearch function is from header file stdlib.h.

Description

C bsearch function performs a binary search on the sorted array *buf and returns a pointer to the first member that matches *key. If the array does not contain the key, a null pointer is returned.

Parameter

• The array must be sorted in ascending order.
• The number of elements in the array is specified by num,
• The size (in bytes) of each element is described by size.

The function pointed to by compare is used to compare an element of the array with the key. The form of the compare function must be as follows:

Return

C bsearch function returns values as described in the following table:

Example

Use C bsearch function to do binary search.

#include <stdlib.h>
#include <ctype.h>
#include <stdio.h>
/*from w w  w  .j  a  v  a  2s .  co  m*/
char *alpha = "abcdefghijklmnopqrstuvwxyz";

int comp(const void *ch, const void *s);

int main(void)
{
  char ch;
  char *p;

  printf("Enter a character: ");
  ch = getchar();
  ch = tolower(ch);
  p = (char *) bsearch(&ch, alpha, 26, 1, comp);
  if(p) printf(" %c is in alphabet\n", *p);
  else printf("is not in alphabet\n");

  return 0;
}

/* Compare two characters. */
int comp(const void *ch, const void *s)
{
  return *(char *)ch - *(char *)s;
}