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...
