An application vendor opened a bug with the product team saying that
the
PathIsUNC
function
was returning incorrect values in Windows Vista.
Specifically, the
PathIsUNC
function was returning FALSE
for strings that begin with \\?\,
whereas Windows XP returned TRUE.
The answer is,
“Yes, the PathIsUNC function returns
FALSE
for strings that begin with \\?\.
Because they aren’t UNCs.”
There was a bug in the Windows XP version of the
PathIsUNC function where it reported that anything
that began with two backslashes was a UNC,
even if it wasn’t.
In particular, paths that begin with \\?\ are not
UNCs,
unless they happen to begin with \\?\UNC\.
The bug was fixed in Windows Vista so it returned TRUE
only if the \\?\ is followed by UNC\.
Fortunately, the application compatibility team had a ready answer
for this:
The
EmulateOldPathIsUNC
compatibility shim returns the PathIsUNC function
to its old behavior that is bug-for-bug compatible with Windows XP.