CodeCogs

linear search and append

You're viewing an older version of this page (#3452). View the current version.

INTERFACE

#include <search.h> void* lsearch( const void *key, const void *base, size_t *nelp, size_t width, int (*compar) (const void *, const void *)) void* lfind( const void *key, const void *base, size_t *nelp, size_t width, int (*compar) (const void *, const void *))

DESCRIPTION

The lsearch and lfind functions walk linearly through an array and compare each element with the one to be sought using a supplied comparison function.

The key argument points to an element that matches the one that is searched. The array's address in memory is denoted by the base argument. The width of one element (i.e. the size as returned by sizeof) is passed as the width argument. The number of valid elements contained in the array (not the number of elements the array has space reserved for) is given in the integer pointed to by nelp. The compar argument points to a function which compares its two arguments and returns zero if they are matching, and non-zero otherwise.

If no matching element was found in the array, lsearch copies key into the position after the last element and increments the integer pointed to by nelp.

Example 1

using lfind (from http://www.digitalmars.com/rtl/search.html )

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

int compare(int *x, int *y) 
{   
   return (*x - *y); 
} 

void main () 
{   
   int array[5] = {44, 69, 3, 17, 23}; 
   size_t elems = 5; 
   int key = 69; 
   int *result; 

   result = (int *)lfind (&key, &array, &elems, sizeof (int), (int(*) (const void *, const void *)) compare); 
   if (result) 
      printf ("Key %d found in linear search\n", key); 
   else 
      printf ("Key %d not found in linear search\n", key); 
}

Output:

Key 69 found in linear search

Example 2

using lsearch (from http://www.digitalmars.com/rtl/search.html )

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

char *animals[10] = 
{   
   "Horse", 
   "Dog", 
   "Cat", 
   "Goat", 
   "Peacock" 
}; 

size_t elems = 5; 

int compare (char **x, char **y) 
{   
   return (strcmp(*x, *y)); 
} 

int addelem(char *key) 
{   
   size_t num = elems; 

   lsearch(&key, animals, &num, sizeof(char *), (int (*)(const void *, const void *)) compare); 
   return (elems == num); 
} 

void main () 
{   
   char *key = "Donkey"; 

   if (addelem(key)) 
     printf (" Animal \"%s\" already exists in array\n", key); 
   else
     printf ("\"%s\" added to animals array\n", key); 
}

Output:

"Donkey" added to animals array

RETURN VALUES

The lsearch and lfind functions return a pointer to the first element found. If no element was found, lsearch returns a pointer to the newly added element, whereas lfind returns <span class="Dv">NULL</span>. Both functions return <span class="Dv">NULL</span> if an error occurs.

HISTORY

The lsearch and lfind functions appeared in 4.2BSD In FreeBSD 5.0 they reappeared conforming to conforming to IEEE Std 1003.1-2001 ('POSIX.1')

STANDARDS

The lsearch and lfind functions conform to IEE Std 1003.1-2001 ('POSIX.1').

lsearch