The current gcc documentation (13.2.1) says: "_Standard Library Header Units_ The Standard Library is not provided as importable header units. If y

The current gcc documentation (13.2.1) says: "_Standard Library Header Units_ The Standard Library is not provided as importable header units. If you want to import such units, you must explicitly build them first. If you do not do this with care, you may have multiple declarations, which the module machinery must merge--compiler resource usage can be affected by how you partition header files into header units." So for now any "import" can work only if one writes appropriate module files first. Nevertheless, I do not expect that the updating of the standard C++ library of gcc will take a long time, so later this new book will become directly usable as it is. For someone who already knows older C++ and just wants to update their knowledge, writing the corresponding module files can be a good learning experience in itself.