Fix required C++ standard

src/test/pq/CMakeLists.txt

@@ -4,7 +4,7 @@ foreach(testsourcefile ${testsources})
   add_executable(${exename} ${testsourcefile})
   target_link_libraries(${exename} PRIVATE taocpp::taopq)
   set_target_properties(${exename} PROPERTIES
-    CXX_STANDARD 17
+    CXX_STANDARD 20
     CXX_STANDARD_REQUIRED ON
     CXX_EXTENSIONS OFF
   )

src/test/pq/single_row_mode.cpp

@@ -0,0 +1,72 @@
+// Copyright (c) 2016-2024 Daniel Frey and Dr. Colin Hirsch
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
+
+#include "../getenv.hpp"
+#include "../macros.hpp"
+
+#include <exception>
+#include <iostream>
+#include <optional>
+#include <tuple>
+#include <utility>
+
+#include <tao/pq.hpp>
+
+namespace
+{
+   void run()
+   {
+      // overwrite the default with an environment variable if needed
+      const auto connection_string = tao::pq::internal::getenv( "TAOPQ_TEST_DATABASE", "dbname=template1" );
+
+      // open a connection to the database
+      const auto conn = tao::pq::connection::create( connection_string );
+
+      conn->execute( "DROP TABLE IF EXISTS tao_single_row_mode" );
+      conn->execute( "CREATE TABLE tao_single_row_mode ( name TEXT PRIMARY KEY, age INTEGER NOT NULL )" );
+
+      conn->prepare( "insert_user", "INSERT INTO tao_single_row_mode ( name, age ) VALUES ( $1, $2 )" );
+      conn->execute( "insert_user", "Daniel", 42 );
+      conn->execute( "insert_user", "Tom", 41 );
+      conn->execute( "insert_user", "Jerry", 29 );
+
+      const auto tr = conn->transaction();
+      tr->send( "SELECT name, age FROM tao_single_row_mode" );
+      tr->set_single_row_mode();
+
+      while( true ) {
+         // in single row mode, each result contains either
+         // a single row or no row when the end is reached.
+         const auto result = tr->get_result();
+         if( result.empty() ) {
+            break;
+         }
+
+         // the loop is unnecessary for single row mode,
+         // but in chunked mode multiple rows per result are possible.
+         for( const auto& row : result ) {
+            std::cout << row[ "name" ].as< std::string >() << " is "
+                      << row[ "age" ].as< unsigned >() << " years old.\n";
+         }
+      }
+   }
+
+}  // namespace
+
+auto main() -> int  // NOLINT(bugprone-exception-escape)
+{
+   try {
+      run();
+   }
+   // LCOV_EXCL_START
+   catch( const std::exception& e ) {
+      std::cerr << "exception: " << e.what() << '\n';
+      throw;
+   }
+   catch( ... ) {
+      std::cerr << "unknown exception\n";
+      throw;
+   }
+   // LCOV_EXCL_STOP
+}