Program to use gdbm database in C++ : chatGpt ans

 Here's a simple C++ program that demonstrates how to perform basic CRUD (Create, Read, Update, Delete) operations using GDBM (GNU Database Manager). This example will show how to store key-value pairs, retrieve them, update them, and delete them using the GDBM API.

C++ Program with GDBM

cpp
#include <gdbm.h>
#include <iostream>
#include <cstring>

class GDBMWrapper {
public:
    GDBMWrapper(const char* filename) {
        db = gdbm_open((char*)filename, 512, GDBM_WRCREAT, 0666, 0);
        if (!db) {
            throw std::runtime_error("Failed to open GDBM database");
        }
    }

    ~GDBMWrapper() {
        if (db) {
            gdbm_close(db);
        }
    }

    void create(const std::string& key, const std::string& value) {
        datum db_key = { (char*)key.c_str(), (int)key.size() };
        datum db_value = { (char*)value.c_str(), (int)value.size() };
        
        if (gdbm_store(db, db_key, db_value, GDBM_INSERT) != 0) {
            throw std::runtime_error("Failed to insert record");
        }
    }

    std::string read(const std::string& key) {
        datum db_key = { (char*)key.c_str(), (int)key.size() };
        datum db_value = gdbm_fetch(db, db_key);
        
        if (!db_value.dptr) {
            throw std::runtime_error("Key not found");
        }

        std::string value(db_value.dptr, db_value.dsize);
        free(db_value.dptr);
        return value;
    }

    void update(const std::string& key, const std::string& new_value) {
        datum db_key = { (char*)key.c_str(), (int)key.size() };
        datum db_value = { (char*)new_value.c_str(), (int)new_value.size() };
        
        if (gdbm_store(db, db_key, db_value, GDBM_REPLACE) != 0) {
            throw std::runtime_error("Failed to update record");
        }
    }

    void remove(const std::string& key) {
        datum db_key = { (char*)key.c_str(), (int)key.size() };
        
        if (gdbm_delete(db, db_key) != 0) {
            throw std::runtime_error("Failed to delete record");
        }
    }

private:
    GDBM_FILE db;
};

int main() {
    try {
        GDBMWrapper db("example.db");

        // Create
        db.create("name", "John Doe");
        db.create("email", "johndoe@example.com");

        // Read
        std::cout << "Name: " << db.read("name") << std::endl;
        std::cout << "Email: " << db.read("email") << std::endl;

        // Update
        db.update("email", "john.doe@newdomain.com");
        std::cout << "Updated Email: " << db.read("email") << std::endl;

        // Delete
        db.remove("name");
        std::cout << "Deleted 'name' record." << std::endl;

        // Try to read the deleted record (will throw an exception)
        try {
            std::cout << "Name: " << db.read("name") << std::endl;
        } catch (const std::exception& e) {
            std::cerr << "Error: " << e.what() << std::endl;
        }

    } catch (const std::exception& e) {
        std::cerr << "Error: " << e.what() << std::endl;
        return 1;
    }

    return 0;
}

Explanation

• GDBMWrapper Class:

  • This class wraps the GDBM functions to make it easier to manage database operations.
  • The constructor opens the database file, and the destructor ensures the database is closed properly.
  • The create, read, update, and remove methods handle the corresponding CRUD operations using the GDBM API.

• CRUD Operations:

  • Create: Inserts a new key-value pair using gdbm_store with GDBM_INSERT.
  • Read: Retrieves a value for a given key using gdbm_fetch.
  • Update: Replaces the value for a given key using gdbm_store with GDBM_REPLACE.
  • Delete: Removes a key-value pair using gdbm_delete.

• Error Handling:

  • The program uses exceptions to handle errors such as failing to open the database, trying to read a non-existent key, etc.

Compilation

To compile this program, you'll need to link against the GDBM library:

sh
g++ -o gdbm_example gdbm_example.cpp -lgdbm

Running the Program

Once compiled, you can run the program:

sh
./gdbm_example

This will perform the CRUD operations, demonstrating how to interact with a GDBM database using C++.