A note about namespaces

The standard C++17 filesystem facilities are all provided in a single header, <filesystem>, and everything in that header is placed in its own namespace: namespace std::filesystem. This follows the precedent set by C++11's <chrono> header with its namespace std::chrono. (This book omits a full treatment of <chrono>. Its interactions with std::thread and std::timed_mutex are covered briefly in Chapter 7, Concurrency.)

This namespacing strategy means that when you use the <filesystem> facilities, you'll be using identifiers such as std::filesystem::directory_iterator and std::filesystem::temp_directory_path(). These fully qualified names are quite unwieldy! But pulling the entire namespace into your current context with a using declaration is probably an overkill, especially, if you have to do it at file scope. We've all been taught over the past decade never to write using namespace std, and that advice won't change, no matter how deeply the...