Introduction

A URL shortener is a tool that converts long URLs into shorter, more manageable links that are easy to share and remember.
In this tutorial, we will create a basic URL shortener using the C programming language. The program will take a long URL as input
and generate a shortened version. This is a great way to learn about string manipulation and file handling in C.

Objective

The objective of this program is to implement a simple URL shortener that maps long URLs to short, custom identifiers.
We’ll be storing the long URL and its corresponding short URL in a file for future reference.

Code

#include 
#include 
#include 

#define MAX_URL_LENGTH 2048
#define SHORT_URL_LENGTH 6

// Function to generate a short URL (simple hash)
void generateShortURL(char *longURL, char *shortURL) {
    unsigned long hash = 5381;
    int c;
    
    // Generate a simple hash from the long URL
    while ((c = *longURL++)) {
        hash = ((hash << 5) + hash) + c;
    }
    
    // Convert hash to a string of characters
    snprintf(shortURL, SHORT_URL_LENGTH, "%lx", hash % 1000000); // Limit the length
}

// Function to store the long and short URL pair
void storeURL(char *longURL, char *shortURL) {
    FILE *file = fopen("urls.txt", "a");
    if (file == NULL) {
        printf("Could not open file for saving URL.\n");
        return;
    }
    
    fprintf(file, "Long URL: %s\nShort URL: %s\n\n", longURL, shortURL);
    fclose(file);
}

int main() {
    char longURL[MAX_URL_LENGTH], shortURL[SHORT_URL_LENGTH];
    
    // Input the long URL
    printf("Enter the long URL: ");
    fgets(longURL, MAX_URL_LENGTH, stdin);
    
    // Remove the newline character
    longURL[strcspn(longURL, "\n")] = 0;
    
    // Generate short URL
    generateShortURL(longURL, shortURL);
    
    // Display the short URL
    printf("Short URL: http://short.ly/%s\n", shortURL);
    
    // Store the URL pair in a file
    storeURL(longURL, shortURL);
    
    return 0;
}
    

Explanation of the Program

This program consists of a few important parts:

• generateShortURL function: This function takes a long URL as input and generates a hash-based short URL. It simply creates a hash from the URL and then converts it into a string of numbers to create a unique short URL.
• storeURL function: This function stores the long URL and its corresponding short URL in a text file named urls.txt. This allows us to persist the mapping between long and short URLs.
• main function: The main function drives the program. It prompts the user to enter a long URL, generates a short URL using the generateShortURL function, displays it to the user, and then stores the mapping in a file using the storeURL function.

How to Run the Program

To run this program, follow these steps:

1. 1. Copy the code into a C file, for example, url_shortener.c.
   2. Open a terminal and navigate to the directory where the file is saved.
   3. Compile the program using a C compiler (e.g., GCC):

gcc url_shortener.c -o url_shortener

1. 1. Run the compiled program:

./url_shortener

1. Enter the long URL when prompted, and the program will generate and display a short URL. It will also store the mapping in the urls.txt file.