C bsearch() function

C bsearch() function - Binary search a sorted table

Syntax bsearch() function

void *bsearch(const void *key, const void *base, size_t nitems, size_t size, int (*compar)(const void *, const void *))

The bsearch() function is used to perform a binary search of an array of num elements, each of size bytes. The array must be sorted ascendingly by the function pointed to by compare.

Parameters bsearch() function

Return value from bsearch()

• This function returns a pointer to an entry in the array that matches the search key.
• If key is not found, a NULL pointer is returned.
• If two keys are equal, the element that key will point to is unspecified.

Example: bsearch() function

The following example shows the usage of bsearch() function.

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

int compare( char **arg1, char **arg2 )
{
   /* Compare all of both strings: */
   return _strcmpi( *arg1, *arg2 );
}

int main( void )
{
   char *colors[] = {"red", "green", "pink", "orange", "red", "white", "black", "blue"};
   char **result;
   char *key = "red";
   char *key1 = "yellow";
   char *key2 = "black";
   int i;

   /* Sort using Quicksort algorithm: */
   qsort( (void *)colors, sizeof(colors)/sizeof(colors[0]), sizeof( char * ), (int (*)(const
   void*, const void*))compare );
   printf("Sorted array elements:\n");
   for( i = 0; i < sizeof(colors)/sizeof(colors[0]); ++i )    /* Output sorted list */
      printf( "%s ", colors[i] );

   printf("\n\nFind the color 'red' using a binary search algorithm:");
   result = (char **)bsearch( (char *) &key, (char *)colors, sizeof(colors)/sizeof(colors[0]),
                              sizeof( char * ), (int (*)(const void*, const void*))compare );
   if( result )
      printf( "\n%s color found at %Fp\n", *result, result );
   else
      printf( "\n'Red' color not found!\n" );
   
   printf("\n\nFind the color 'yellow' using a binary search algorithm:");
   result = (char **)bsearch( (char *) &key1, (char *)colors, sizeof(colors)/sizeof(colors[0]),
                              sizeof( char * ), (int (*)(const void*, const void*))compare );
   if( result )
      printf( "\n%s color found at %Fp\n", *result, result );
   else
      printf( "\n'yellow' color not found!\n" );
   
   printf("\n\nFind the color 'black' using a binary search algorithm:");   
   result = (char **)bsearch( (char *) &key2, (char *)colors, sizeof(colors)/sizeof(colors[0]),
                              sizeof( char * ), (int (*)(const void*, const void*))compare );
   if( result )
      printf( "\n%s color found at %Fp\n", *result, result );
   else
      printf( "\n'black' color not found!\n" );
}

N.B.: This code is executed in windows 10

Output:

Sorted array elements:
black blue green orange pink red red white

Find the color 'red' using a binary search algorithm:
red color found at 000000000062FDD8


Find the color 'yellow' using a binary search algorithm:
'yellow' color not found!


Find the color 'black' using a binary search algorithm:
black color found at 000000000062FDB0

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