Win32 API: Reading very long "Win32 file namespace" names

Question

Sorry I haven't tested this myself, but MSDN says we can make a very long (more than MAX_PATH ie. 260 chars) file name by specifying "Win32 file namespace":

• http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247.aspx#win32_file_namespaces Naming Files, Paths, and Namespaces > Win32 File Namespaces

That's easy with the CreateFile API because its signature accepts LPCTSTR lpFileName which incurs no restriction about the input length:

• http://msdn.microsoft.com/en-us/library/windows/desktop/aa363858.aspx CreateFile function (Windows)

But how can we read such a long file name? W32_FIND_DATA returned by FindFirstFile contains only TCHAR cFileName[MAX_PATH].

• http://msdn.microsoft.com/en-us/library/windows/desktop/aa365740.aspx WIN32_FIND_DATA structure (Windows)
• http://msdn.microsoft.com/en-us/library/windows/desktop/aa364418.aspx FindFirstFile function (Windows)

Will we perhaps get 8.3 name instead when the actual file name doesn't fit into cFileName[MAX_PATH]?

Answer 1

For CreateFile, you can escape the MAX_PATH limit by using the Unicode version of the API, and the special L"\\?\" prefix.

For W32_FIND_DATA things are a little different. That record contains the file names as inline character arrays. With fixed length. However, these filenames in the record only contain the name of the object relative to its container. By that I mean these filenames are relative to the directory in which they live. And so the limitation that they can be no more than MAX_PATH in length is in fact not a limitation, because each component in a path is itself limited in length, typically to be no more than 255 characters.

The limitation of path components to 255 characters in length is discussed in the very MSDN article to which you linked: Naming Files, Paths, and Namespaces.

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".