How to Use bsearch with an Array of Struct in C? (original) (raw)

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 `

// 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)