...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
This example demonstrates how to use any_connection
.
The example employs async functions with stackful coroutines.
This example assumes you have gone through the setup.
// any_connection is a connection type that is easier to use than regular // connection. It is type-erased: it's not a template, and is able to connect // to any server using TCP, UNIX sockets and SSL. It features a simplified // connect and async_connect function family, which handle name resolution. // Performance is equivalent to regular connection. // // This example demonstrates how to connect to a server using any_connection. // It uses asynchronous functions and coroutines (with boost::asio::spawn). // Recall that using these coroutines requires linking against Boost.Context. // // any_connection is an experimental feature. #include <boost/mysql/any_address.hpp> #include <boost/mysql/any_connection.hpp> #include <boost/mysql/diagnostics.hpp> #include <boost/mysql/error_code.hpp> #include <boost/mysql/error_with_diagnostics.hpp> #include <boost/mysql/results.hpp> #include <boost/mysql/row_view.hpp> #include <boost/mysql/throw_on_error.hpp> #include <boost/asio/error.hpp> #include <boost/asio/io_context.hpp> #include <boost/asio/spawn.hpp> #include <iostream> using boost::mysql::error_code; void print_employee(boost::mysql::row_view employee) { std::cout << "Employee '" << employee.at(0) << " " // first_name (string) << employee.at(1) << "' earns " // last_name (string) << employee.at(2) << " dollars yearly\n"; // salary (double) } void main_impl(int argc, char** argv) { if (argc != 4 && argc != 5) { std::cerr << "Usage: " << argv[0] << " <username> <password> <server-hostname> [company-id]\n"; exit(1); } const char* hostname = argv[3]; // The company_id whose employees we will be listing. This // is user-supplied input, and should be treated as untrusted. const char* company_id = argc == 5 ? argv[4] : "HGS"; // I/O context boost::asio::io_context ctx; // Connection. Note that the connection's type doesn't depend // on the transport (TCP or UNIX sockets). boost::mysql::any_connection conn(ctx); // Connection configuration. This contains the server address, // credentials, and other configuration used during connection establishment. // Note that, by default, TCP connections will use TLS. connect_params::ssl // allows disabling it. boost::mysql::connect_params params; // The server address. This can either be a host and port or a UNIX socket path params.server_address.emplace_host_and_port(hostname); // Username to log in as params.username = argv[1]; // Password to use params.password = argv[2]; // Database to use; leave empty or omit for no database params.database = "boost_mysql_examples"; /** * The entry point. We spawn a stackful coroutine using boost::asio::spawn. * * The coroutine will actually start running when we call io_context::run(). * It will suspend every time we call one of the asynchronous functions, saving * all information it needs for resuming. When the asynchronous operation completes, * the coroutine will resume in the point it was left. */ boost::asio::spawn( ctx.get_executor(), [&conn, ¶ms, company_id](boost::asio::yield_context yield) { // This error_code and diagnostics will be filled if an // operation fails. We will check them for every operation we perform. boost::mysql::error_code ec; boost::mysql::diagnostics diag; // Connect to the server. This will take care of resolving the provided // hostname to an IP address, connect to that address, and establish // the MySQL session. conn.async_connect(params, diag, yield[ec]); boost::mysql::throw_on_error(ec, diag); // We will be using company_id, which is untrusted user input, so we will use a prepared // statement. boost::mysql::statement stmt = conn.async_prepare_statement( "SELECT first_name, last_name, salary FROM employee WHERE company_id = ?", diag, yield[ec] ); boost::mysql::throw_on_error(ec, diag); // Execute the statement boost::mysql::results result; conn.async_execute(stmt.bind(company_id), result, diag, yield[ec]); boost::mysql::throw_on_error(ec, diag); // Print the employees for (boost::mysql::row_view employee : result.rows()) { print_employee(employee); } // Notify the MySQL server we want to quit, then close the underlying connection. conn.async_close(diag, yield[ec]); boost::mysql::throw_on_error(ec, diag); }, // If any exception is thrown in the coroutine body, rethrow it. [](std::exception_ptr ptr) { if (ptr) { std::rethrow_exception(ptr); } } ); // Don't forget to call run()! Otherwise, your program // will not spawn the coroutine and will do nothing. ctx.run(); } int main(int argc, char** argv) { try { main_impl(argc, argv); } catch (const boost::mysql::error_with_diagnostics& err) { // You will only get this type of exceptions if you use throw_on_error. // Some errors include additional diagnostics, like server-provided error messages. // Security note: diagnostics::server_message may contain user-supplied values (e.g. the // field value that caused the error) and is encoded using to the connection's character set // (UTF-8 by default). Treat is as untrusted input. std::cerr << "Error: " << err.what() << '\n' << "Server diagnostics: " << err.get_diagnostics().server_message() << std::endl; return 1; } catch (const std::exception& err) { std::cerr << "Error: " << err.what() << std::endl; return 1; } }