EXPLANATION
In the Windows API (with some exceptions discussed in the following paragraphs), the maximum length for a path is
MAX_PATH,
which is defined as 260 characters. A local path is structured in the
following order: drive letter, colon, backslash, name components
separated by backslashes, and a terminating null character. For example,
the maximum path on drive D is "D:\
some 256-character path string<NUL>"
where "<NUL>" represents the invisible terminating null character
for the current system codepage. (The characters < > are used
here for visual clarity and cannot be part of a valid path string.)
Note
File I/O functions in the Windows API convert "/" to "\" as part of
converting the name to an NT-style name, except when using the "\\?\"
prefix as detailed in the following sections.
The Windows API has many functions that also have Unicode versions to
permit an extended-length path for a maximum total path length of
32,767 characters. This type of path is composed of components separated
by backslashes, each up to the value returned in the
lpMaximumComponentLength parameter of the
GetVolumeInformation
function (this value is commonly 255 characters). To specify an
extended-length path, use the "\\?\" prefix. For example, "\\?\D:\
very long path".
Note
The maximum path of 32,767 characters is approximate, because the
"\\?\" prefix may be expanded to a longer string by the system at run
time, and this expansion applies to the total length.
The "\\?\" prefix can also be used with paths constructed according
to the universal naming convention (UNC). To specify such a path using
UNC, use the "\\?\UNC\" prefix. For example, "\\?\UNC\server\share",
where "server" is the name of the computer and "share" is the name of
the shared folder. These prefixes are not used as part of the path
itself. They indicate that the path should be passed to the system with
minimal modification, which means that you cannot use forward slashes to
represent path separators, or a period to represent the current
directory, or double dots to represent the parent directory. Because you
cannot use the "\\?\" prefix with a relative path, relative paths are
always limited to a total of
MAX_PATH characters.
There is no need to perform any Unicode normalization on path and
file name strings for use by the Windows file I/O API functions because
the file system treats path and file names as an opaque sequence of
WCHARs.
Any normalization that your application requires should be performed
with this in mind, external of any calls to related Windows file I/O API
functions.
When using an API to create a directory, the specified path cannot be
so long that you cannot append an 8.3 file name (that is, the directory
name cannot exceed
MAX_PATH minus 12).
The shell and the file system have different requirements. It is
possible to create a path with the Windows API that the shell user
interface is not able to interpret properly.
