\\?\UNC\server\share - verylongpath errors out

Question

In Windows Explorer the UNC long path construction errors out as:
Windows cannot access \\?\UNC\server\share
(Error: 0x80004005)
Background:
https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
To specify an extended-length path, use the "\\?\" prefix. For example, "\\?\D:\very long path".
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.
What am I missing here? The UNC prefix never worked for me.

Answer 1

Hi,
It is a Windows explorer restriction (MAX_PATH). Windows explorer is different than the file system for its API. If you prefix the file name with "\\?\" and call the Unicode versions of the Windows APIs, then you can use file names up to 32K characters
in length. In other words, the \\?\ prefix is a way to enable long paths while working with the Windows file APIs. 
If you need to use the out-of-length type file in Windows explorer, your need to make the name shorter to remove a file like this from the server itself.
For more detailed information, you could refer to the Microsoft support answer in the thread below:
Increase 255 Character limitation on file servers
https://social.technet.microsoft.com/Forums/itmanagement/en-US/bad56182-5ea1-42ff-8f4d-acd0463d067e/increase-255-character-limitation-on-file-servers?forum=winserverfiles
Best Regards,
Mandy
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