How to Use bsearch with an Array of Struct in C?

Last Updated : 01 Mar, 2024

The bsearch function in C is a standard library function defined in the stdlib.h header file that is used to perform binary search on array-like structure. In this article, we will learn to use bsearch with an array of struct in C.

Input:
struct Person people[] = { { 1, "Ram" }, { 2, "Rohan" }, { 4, "Ria" }, { 3, "Mohan" } };
Key: 3

Output:
Person found: ID = 3
Name = Mohan

bsearch on Array of Structure in C

To use std::bsearch() with an array of structure, we have to first sort the given array of structs and then write a comparator function that helps the bsearch to find the matching value. After that, we can call the std::bsearch that returns a pointer to the element if it is found otherwise it will return NULL.

Syntax of search()

bsearch(keyToFind, arrayName, arraySize, sizeof(struct structName), compareFunction);

Here,

structName is the name of the structure.
arrayName is the name of sorted array of struct.
keyToFind is the element we want to search.
arraySize is the size of each element in the array of struct.
compareFunction is the function that compares the values

C Program to Use bsearch with a Array of Struct

The below example demonstrates the use of bsearch() with an array of structure in C.

// C Program to illustrate how to use bsearch with a
// structure
#include <stdio.h>
#include <stdlib.h>

// Define the Person struct
struct Person {
    int id;
    char name[50];
};

// Comparison function for bsearch
int comparePersons(const void* a, const void* b)
{
    // Convert the void pointers to Person pointers
    int idA = ((struct Person*)a)->id;
    int idB = ((struct Person*)b)->id;

    // Compare the IDs for sorting
    return (idA - idB);
}

int main()
{
    // Array of Person structs (assumed to be sorted by id)
    struct Person people[] = {
        { 1, "Ram" },
        { 2, "Rohan" },
        { 4, "Ria" },
        { 3, "Mohan" },
    };

    // Calculate the number of elements in the array
    int n = sizeof(people) / sizeof(people[0]);

    // Sort the array before using bsearch
    qsort(people, n, sizeof(struct Person), comparePersons);

    // Define the key to search for
    struct Person keyPerson = {
        .id = 3, .name = ""
    }; // Using designated initializer for clarity

    // Use bsearch to find the person with the specified ID
    struct Person* result = (struct Person*)bsearch(
        &keyPerson, people, n, sizeof(struct Person),
        comparePersons);

    // Check if the person was found
    if (result != NULL) {
        printf("Person found: ID=%d, Name=%s\n", result->id,
               result->name);
    }
    else {
        printf("Person not found.\n");
    }

    return 0;
}

Output

Person found: ID=3, Name=Mohan

Time complexity: O(log⁡(N)), where N is the number of elements in the array of structs.
Auxilliary Space: O(1)