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Version 4 is a significant revision of the Boost Filesystem library that makes its interface and behavior closer to std::filesystem that was introduced in C++17 and updated in the later standards. It removes the features that were deprecated in Version 3 and makes a number of breaking changes. Eventually, Version 4 will become the default, and Version 3 will be removed.
Users can select Boost.Filesystem v4 version by defining BOOST_FILESYSTEM_VERSION
macro to 4 when compiling their code. There is no need to separately compile
Boost.Filesystem for each library version — a single binary supports both
v3 and v4. Users should avoid using both v3 and v4 in the same application
as this can lead to subtle bugs.
path::filename
no longer returns root name or root directory if the path contains
no other elements. For example, on Windows path("C:").filename() used to return "C:" and
path("C:\\").filename()
used to return "\" and both will return an empty path now.
This also affects path::stem
and path::extension
methods, as those are based on path::filename.
path::stem
and path::extension
no longer treat a filename that starts with a dot and has no other
dots as an extension. Filenames starting with a dot are commonly treated
as filenames with an empty extension. The leading dot is used to indicate
a hidden file on most UNIX-like systems.
path::filename
and path::iterator no longer return an implicit
trailing dot (".") element if the path ends with a directory
separator. Instead, an empty path is returned, similar to C++17 std::filesystem.
This also affects other methods that are defined in terms of iterators
or filename, such as path::stem,
path::compare
or lexicographical_compare.
For example, path("a/b/")
== path("a/b/.") no longer holds true.
path::lexically_normal
no longer produces a trailing dot (".") element and omits
a directory separator after a trailing dot-dot ("..") element
in the normalized paths.
path::lexically_normal,
path::make_preferred,
path::generic_path
and similar methods no longer convert between forward and backward
slashes in root names of the returned paths.
path::append
consider root name and root directory of the appended path. If the
appended path is absolute, or root name is present and differs from
the source path, the resulting path is equivalent to the appended path.
If root directory is present, the result is the root directory and
relative path rebased on top of the root name of the source path. Otherwise,
the behavior is similar to v3. This behavior is similar to C++17 std::filesystem.
path no longer supports
construction, assignment or appending from containers of characters.
Use string types or iterators as the source for these opereations instead.
path::remove_filename
preserves the trailing directory separator, so that path::has_filename
returns false after a
successful call to path::remove_filename.
directory_entry
constructors and modifiers that initialize or modify path of the directory
entry automatically call directory_entry::refresh
instead of clearing cached file statuses. This means that the file
identified by the new path needs to be accessible in the filesystem
at the point of the call.
directory_entry
constructors and modifiers that accept file_status
arguments to initialize cached file statuses are removed. The amount
of cached data is an implementation detail of directory_entry,
and in the future it may not be limited to just file statuses. Users
should rely on automatic refreshes of the cached data.
equivalent
now fails if only one of the input paths exists.