Filesystem library

The new filesystem library is based on boost::filesystem. Some of its components are optional. This means not all functionality of std::filesystem is available on each implementation of the filesystem library. For example, FAT-32 does not support symbolic links.

ℹ️ Using cppreference.com
At the time of the writing this book (October 2017), I had no C+±compiler at my disposal that supports the new filesystem library; therefore, I executed the programs in this chapter with the newest GCC-compiler on cppreference.com: filesystem that supports the new filesystem library.

To use the new filesystem library you may have to include and apply the experimental namespace.

#include <experimental/filesystem>
namespace fs = std::experimental::filesystem;

All examples in this chapter are written without the experimental namespace.

The library is based on the three concepts: file, file name, and path.

• A file is an object that holds data such that you can write to it or read from it. A file has a name and a file type. A file type can be a directory, hard link, symbolic link or a regular file.

  • A directory is a container for holding other files. The current directory is represented by a dot "."; the parent directory is represented by two dots "..".

  • A hard link associates a name with an existing file.

  • A symbolic link associates a name with a path that may exist.

  • A regular file is a directory entry which is neither a directory, a hard link, nor a symbolic link.

• A file name is a string that represents a file. It is implementation-defined which characters are allowed, how long the name could be or if the name is case sensitive.

• A path is a sequence of entries that identify the location for a file. It has an optional root-name such a “C:” on Windows, followed by a root-directory such a “/” on Unix. Additional parts can be directories, hard links, symbolic links, or regular files. A path can be absolute, canonical, or relative.

  • An absolute path is a path that identifies a file.

  • A canonical path is a path that includes neither a symbolic link nor the relative paths "." (current directory) or ".."(parent directory).

  • A relative path specifies a path relative to a location in the file system. Paths such as "." (current directory), ".."(parent directory) or "home/rainer" are relative paths. On Unix, they do not start at the root-directory "/".

Here is an introductory example of the filesystem.