C library - bsearch() function

The C stdlib library bsearch() function performs a binary search on a sorted array. It is used to find a specific element within the array. This function searches through an array of n objects pointed to by base. It looks for an element matching the object pointed to by key.

A binary search is a searching algorithm used to find the position of the targeted value within the sorted array.

Syntax

Following is the C library syntax of the bsearch() function −

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

Parameters

This function accepts following parameters −

• key − It represents pointer to the element that need to be search.

• base − It represents pointer to the first element of the array.

• nitems − It represents number of element in the array.

• size − It represents size of each element in the array.

• compare − It represent a function that compares two elements.

Return Value

This function returns a pointer to the matched element in the array. Otherwise, it returns NULL pointer.

Example 1

In this example, we create a basic c program to demonstrate the use of bsearch() function.

#include <stdio.h>
#include <stdlib.h>
int compare(const void * a, const void * b) {
   return ( *(int*)a - *(int*)b );
}
// main function
int main () {
   int values[] = { 5, 20, 10, 30, 40 };
   int *item;
   int key = 30;

   /* using bsearch() to find value 30 in the array */
   item = (int*) bsearch (&key, values, 5, sizeof (int), compare);
   if( item != NULL ) {
      printf("Found item = %d\n", *item);
   } 
   else {
      printf("Item = %d could not be found\n", *item);
   }   
   return(0);
}

Output

Following is the output −

Found item = 30

Example 2

The below c program uses the bsearch() function to search for a character in a sorted array.

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

// Comparison function
int comfunc(const void* a, const void* b) {
   return (*(char*)a - *(char*)b);
}
// main function
int main() {
   // sorted array
   char arr[] = {'a', 'b', 'c', 'd', 'e'};
   int n = sizeof(arr) / sizeof(arr[0]);

   // searching key
   char key = 'c';

   // using bsearch()
   char* item = (char*)bsearch(&key, arr, n, sizeof(char), comfunc);

   // If the key is found, print its value and index
   if (item != NULL) {
      printf("'%c' Found at index %ld\n", *item, item - arr);
   }
   else {
      printf("Character '%c' is not found\n", key);
   }
   return 0;
}

Output

Following is the output −

'c' Found at index 2

Example 3

Following is the another example, we create a c program to use the bsearch() function to search for a string in a sorted array.

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

// Comparison function
int comfunc(const void* a, const void* b) {
   return strcmp(*(const char**)a, *(const char**)b);
}
// main function
int main() {
   // Sorted array of strings
   const char* arr[] = {"Aman", "Shriansh", "Tapas", "Vivek"};
   int n = sizeof(arr) / sizeof(arr[0]);

   // Searching key
   const char* key = "Aman";

   // Using bsearch()
   const char** item;
   item = (const char**)bsearch(&key, arr, n, sizeof(const char*), comfunc);

   // If the key is found, print its value and index
   if (item != NULL) {
      printf("'%s' Found at index %ld\n", *item, item - arr);
   } 
   else {
      printf("Name '%s' is not found\n", key);
   }
   return 0;
}

Output

Following is the output −

'Aman' Found at index 0