Streams are one of the most powerful (and complicated) components of the C++ standard library. Using them for plain, unformatted input and output is generally straightforward, but changing the format to suit your needs with standard manipulators, or writing your own manipulators, is not. Therefore, the first few recipes describe different ways to format stream output. The two after that describe how to write objects of a class to a stream or read them from one.
Then the recipes shift from reading and writing file content to operating on the files themselves (and directories). If your program uses files, especially if it's a daemon or server-side process, you will probably create files and directories, clean them up, rename them, and so on. There are a number of recipes that explain how to do these unglamorous, but necessary, tasks in C++.
The last third of the recipes demonstrate how to manipulate file and pathnames themselves using many of the standard string member functions. Standard strings contain an abundance of functions for inspecting and manipulating their contents, and if you have to parse path and filenames they come in handy. If what you need is not discussed in these recipes, take a look at Chapter 7, too--what you're after might be described there.
File manipulation requires direct interaction with the operating system (OS), and there are often subtle differences (and occasionally glaring incompatibilities) between OSs. Many of the typical file and directory manipulation needs are part of the standard C system calls, and work the same or similarly on different systems. Where there are differences between OSs' versions of libraries, I note it in the recipes.
As I have discussed in previous chapters, Boost is an open source project that has generated a number of high-quality, portable libraries. But since this is a book about C++ and not the Boost project, I have preferred standard C++ solutions whenever possible. In many cases, however, (most notably Recipe 10.12) there isn't a Standard C++ solution, so I have used the Boost Filesystem library written by Beman Dawes, which provides a portable filesystem interface, to give a portable solution. Take a look at the Boost Filesystem library if you have to do portable filesystem interaction--you will save yourself lots of time and effort. For more information on the Boost project, see www.boost.org.