C++ Tutor

Databases

C++ Database Connections

Connecting to Databases

C++ database connections use driver-specific APIs.

Understanding C++ Database Drivers

To connect a C++ application to a database, specific drivers are required. These drivers act as intermediaries between your application and the database, handling communication and transactions. Popular database systems like MySQL, PostgreSQL, and SQLite have their own C++ APIs.

Setting Up a MySQL Connection

To connect to a MySQL database, you must use the MySQL Connector/C++. This library provides the necessary API to connect and interact with MySQL databases using C++.

#include <mysql_driver.h>
#include <mysql_connection.h>
#include <cppconn/statement.h>
#include <cppconn/resultset.h>

int main() {
    sql::mysql::MySQL_Driver *driver;
    sql::Connection *con;
    sql::Statement *stmt;
    sql::ResultSet *res;

    driver = sql::mysql::get_mysql_driver_instance();
    con = driver->connect("tcp://127.0.0.1:3306", "user", "password");
    con->setSchema("database_name");

    stmt = con->createStatement();
    res = stmt->executeQuery("SELECT 'Hello World!' AS _message");
    while (res->next()) {
        std::cout << "Message: " << res->getString("_message") << std::endl;
    }

    delete res;
    delete stmt;
    delete con;

    return 0;
}

Connecting to a PostgreSQL Database

For PostgreSQL, the libpq library is the standard way to connect to a PostgreSQL database from a C++ application. This library is robust and provides extensive functionality for database operations.

#include <iostream>
#include <libpq-fe.h>

int main() {
    PGconn *conn = PQconnectdb("user=username password=secret dbname=mydb hostaddr=127.0.0.1 port=5432");
    if (PQstatus(conn) != CONNECTION_OK) {
        std::cerr << "Connection to database failed: " << PQerrorMessage(conn) << std::endl;
        PQfinish(conn);
        return 1;
    }

    PGresult *res = PQexec(conn, "SELECT version();");
    if (PQresultStatus(res) != PGRES_TUPLES_OK) {
        std::cerr << "SELECT failed: " << PQerrorMessage(conn) << std::endl;
        PQclear(res);
        PQfinish(conn);
        return 1;
    }

    std::cout << "PostgreSQL version: " << PQgetvalue(res, 0, 0) << std::endl;

    PQclear(res);
    PQfinish(conn);
    return 0;
}

Working with SQLite in C++

SQLite is a serverless database engine that is self-contained and requires minimal setup. The SQLite C/C++ library is simple to integrate and use within C++ projects.

#include <iostream>
#include <sqlite3.h>

int main() {
    sqlite3 *db;
    char *errMsg = 0;
    int rc = sqlite3_open("test.db", &db);

    if (rc) {
        std::cerr << "Can't open database: " << sqlite3_errmsg(db) << std::endl;
        return 1;
    } else {
        std::cout << "Opened database successfully" << std::endl;
    }

    const char *sql = "CREATE TABLE IF NOT EXISTS COMPANY("  
                      "ID INT PRIMARY KEY NOT NULL," 
                      "NAME TEXT NOT NULL," 
                      "AGE INT NOT NULL," 
                      "ADDRESS CHAR(50)," 
                      "SALARY REAL );";

    rc = sqlite3_exec(db, sql, 0, 0, &errMsg);
    if (rc != SQLITE_OK) {
        std::cerr << "SQL error: " << errMsg << std::endl;
        sqlite3_free(errMsg);
    } else {
        std::cout << "Table created successfully" << std::endl;
    }

    sqlite3_close(db);
    return 0;
}

Conclusion

Connecting C++ applications to databases involves using the right driver and API for your chosen database system. Each database has its own unique setup and API calls, but with the right configuration, C++ can efficiently handle database operations.

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