How to Write a C Function for String Searching Without string.h

Discover how to implement a string search function in C from scratch, without using the `string.h` library, and streamline your code for efficiency.
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Introduction

When working with strings in C, you often rely on the string.h library for various functions. However, there may be scenarios where avoiding this library is desirable. Perhaps you're trying to minimize dependencies or you're practicing your coding skills. In this guide, we will address how to implement a string search function that finds occurrences of a substring (needle) within a larger string (haystack) without using string.h.

The Problem

You want to create a function that accepts two parameters:

needle: the substring you're searching for.

haystack: the larger string in which you are searching.

The function should return:

The starting index of the first occurrence of needle in haystack.

-1 if needle is not found in haystack.

The original code utilizes strlen, which is part of string.h. Our goal is to rewrite this functionality without relying on that library.

The Solution

Step-by-Step Implementation

Let's break down the solution into manageable steps, and I will provide a clear implementation example for you.

Initialize Variables:

Use counters for the current position in both strings (i for haystack, matched for needle).

Iterate Through the Haystack:

Use a loop to traverse through haystack.

Character Matching:

Check if characters match between haystack and needle.

If they do, increment both counters.

If they don’t, and if matched is greater than 0, rewind the position in haystack to attempt matching again.

Return Results:

Once the loop is complete, check if the entire needle was matched. If so, return the starting index; otherwise, return -1.

Here’s the Code Implementation

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code

Function str_find: This function iterates through haystack while looking for the needle. It adjusts its position and character matches based on the logic described above.

Main Function: The main function sets up test cases and prints whether each needle is found or not.

Understanding the Output

When you run the code above, you will receive output indicating which needles were found. For example:

[[See Video to Reveal this Text or Code Snippet]]

This output shows that "far", "lucas", and "banana" were found, while "yoda" and "force" were not.

Conclusion

By implementing the string search function without the use of string.h, you gain a deeper understanding of character manipulation and string handling in C. This exercise not only sharpens your coding skills but also enhances your ability to optimize code in situations where libraries may not be accessible.

Feel free to experiment further, such as modifying the function to find multiple instances of the needle or handling edge cases!