Working with Databases in C++: PostgreSQL and MongoDB for Beginners

Introduction to Working with Databases in C++

Modern applications rarely do without data storage. C++ is a powerful systems programming language that is well-suited for high-load projects working with databases. In this article, we will look at how to connect to two popular DBMSs — the relational PostgreSQL and the document-oriented MongoDB — and perform basic operations (CRUD).

The material is designed for beginners: you will learn which libraries are needed, how to install them, and see ready-made code examples. After reading, you will be able to independently integrate C++ with any of these databases.

PostgreSQL in C++: The Relational Approach

PostgreSQL is one of the most reliable open-source relational DBMSs. To work with it from C++, the libpqxx library is used — an official wrapper over the C library libpq.

Installing libpqxx

On Linux (Ubuntu/Debian), installation is done with a single command:

sudo apt-get install libpqxx-dev

For Windows, you can use vcpkg:

vcpkg install libpqxx

Connecting and Executing a Query

Let's look at a simple example: connecting to a database, creating a table, and inserting data.

#include <iostream>\n#include <pqxx/pqxx>\n\nint main() {\n    try {\n        // Connecting to the database (replace parameters with your own)\n        pqxx::connection conn("dbname=testdb user=postgres password=secret hostaddr=127.0.0.1 port=5432");\n        \n        if (conn.is_open()) {\n            std::cout << "Connection to PostgreSQL successful!" << std::endl;\n        }\n\n        // Creating a transaction\n        pqxx::work txn(conn);\n\n        // Creating a table\n        txn.exec("CREATE TABLE IF NOT EXISTS users ("\n                 "id SERIAL PRIMARY KEY, "\n                 "name VARCHAR(100) NOT NULL, "\n                 "email VARCHAR(100) UNIQUE NOT NULL)");\n\n        // Inserting data\n        txn.exec("INSERT INTO users (name, email) VALUES "\n                 "('Ivan Petrov', 'ivan@example.com'), "\n                 "('Maria Smirnova', 'maria@example.com')");\n\n        // Committing the transaction\n        txn.commit();\n        std::cout << "Data added successfully!" << std::endl;\n\n    } catch (const std::exception &e) {\n        std::cerr << "Error: " << e.what() << std::endl;\n        return 1;\n    }\n    return 0;\n}

Reading Data (SELECT)

To retrieve data, use the result iterator:

pqxx::work txn(conn);\npqxx::result result = txn.exec("SELECT id, name, email FROM users");\n\nfor (const auto &row : result) {\n    int id = row["id"].as<int>();\n    std::string name = row["name"].as<std::string>();\n    std::string email = row["email"].as<std::string>();\n    std::cout << id << " | " << name << " | " << email << std::endl;\n}

Important: Always use parameterized queries to protect against SQL injection:

txn.exec_params("INSERT INTO users (name, email) VALUES ($1, $2)",\n                "Alexey", "alex@example.com");

MongoDB in C++: The Document-Oriented Approach

MongoDB is a NoSQL database that stores data in BSON format (binary JSON). For C++, there is an official driver mongocxx.

Installing mongocxx

Installation on Linux (requires the MongoDB C Driver to be installed first):

sudo apt-get install libmongoc-dev libbson-dev\ngit clone https://github.com/mongodb/mongo-cxx-driver.git\ncd mongo-cxx-driver\nmkdir build && cd build\ncmake .. -DCMAKE_BUILD_TYPE=Release -DBSONCXX_POLY_USE_MNMLSTC=ON\nmake -j4\nsudo make install

Connecting and CRUD Operations

The following code demonstrates connecting to