"Search" example in C

header file : #include <search.h>

reference :

• http://www.gnu.org/software/libc/manual/html_node/Searching-and-Sorting.html#Searching-and-Sorting
• http://www.codecogs.com/reference/c/search.h/

Defining how to compare two int objects:

int
compare_ints (const void *a, const void *b)
{
  const int *da = (const int *) a;
  const int *db = (const int *) b;
 
  return (*da > *db) - (*da < *db);
}

return :

• negative if a “less” than b
• zero if a and b are "equal"
• positive if a "greater" than b

Inside C code

#include<stdio.h>
#include<search.h>

#define ARRAYMAX 10

int
compare_ints (const void *a, const void *b)
{
  const int *da = (const int *) a;
  const int *db = (const int *) b;
 
  return (*da > *db) - (*da < *db);
}



int
main(void)
{

  int *result;
  int data_array[ARRAYMAX] = {1,2,3,4,5,6,7,8,9,10};
  int array_size =ARRAYMAX;

  int key = 9;
 
  result = (int*) lfind(&key, &data_array, &array_size, sizeof (int), compare_ints);

  if(result)
    printf("key %d is found in the data array.\n", key);
  else
    printf("key %d is not in the data array.\n", key);
 
  return 0;
}