...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 use the asynchronous functions using futures.
This example assumes you have gone through the setup.
#include <boost/mysql/error_code.hpp> #include <boost/mysql/handshake_params.hpp> #include <boost/mysql/results.hpp> #include <boost/mysql/row_view.hpp> #include <boost/mysql/statement.hpp> #include <boost/mysql/tcp_ssl.hpp> #include <boost/asio/io_context.hpp> #include <boost/asio/ip/tcp.hpp> #include <boost/asio/ssl/context.hpp> #include <boost/asio/use_future.hpp> #include <boost/system/system_error.hpp> #include <iostream> #include <thread> using boost::asio::use_future; 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) } /** * A boost::asio::io_context plus a thread that calls context.run(). * We encapsulate this here to ensure correct shutdown even in case of * error (exception), when we should first reset the work guard, then * stop the io_context, and then join the thread. Failing to do so * may cause your application to not stop (if the work guard is not * reset) or to terminate badly (if the thread is not joined). */ class application { boost::asio::io_context ctx_; boost::asio::executor_work_guard<boost::asio::io_context::executor_type> guard_; std::thread runner_; public: application() : guard_(ctx_.get_executor()), runner_([this] { ctx_.run(); }) {} application(const application&) = delete; application(application&&) = delete; application& operator=(const application&) = delete; application& operator=(application&&) = delete; ~application() { guard_.reset(); runner_.join(); } boost::asio::io_context& context() { return ctx_; } }; 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); } // 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"; // Context and connections application app; // boost::asio::io_context and a thread that calls run() boost::asio::ssl::context ssl_ctx(boost::asio::ssl::context::tls_client); boost::mysql::tcp_ssl_connection conn(app.context(), ssl_ctx); // Resolver for hostname resolution boost::asio::ip::tcp::resolver resolver(app.context().get_executor()); // Connection params boost::mysql::handshake_params params( argv[1], // username argv[2], // password "boost_mysql_examples" // database to use; leave empty or omit for no database ); /** * Hostname resolution. * Calling async_resolve triggers the * operation, and calling future::get() blocks the current thread until * it completes. get() will throw an exception if the operation fails. */ auto endpoints_fut = resolver.async_resolve( argv[3], boost::mysql::default_port_string, boost::asio::use_future ); auto endpoints = endpoints_fut.get(); // Perform the TCP connect and MySQL handshake. std::future<void> fut = conn.async_connect(*endpoints.begin(), params, use_future); fut.get(); // We will be using company_id, which is untrusted user input, so we will use a prepared // statement. std::future<boost::mysql::statement> stmt_fut = conn.async_prepare_statement( "SELECT first_name, last_name, salary FROM employee WHERE company_id = ?", use_future ); boost::mysql::statement stmt = stmt_fut.get(); // Execute the statement boost::mysql::results result; fut = conn.async_execute(stmt.bind(company_id), result, use_future); fut.get(); // Print 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(use_future).get(); // application dtor. stops io_context and then joins the thread } int main(int argc, char** argv) { try { main_impl(argc, argv); } catch (const std::exception& err) { std::cerr << "Error: " << err.what() << std::endl; return 1; } }