RtlDosPathNameToNtPathName_U on "\\?\C:" Returns Invalid Path

Why is it that when I call RtlDosPathNameToNtPathName_U on the path \\?\C:, instead of getting back

\??\C:

I get back

\??\C:\฀\\?\C:

which is clearly incorrect?

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Code snippet (in D):

struct CurDir { UnicodeString DosPath; HANDLE Handle;开发者_StackOverflow中文版 }

extern (Windows) static bool RtlDosPathNameToNtPathName_U(
    in const(wchar)* DosPathName, out UnicodeString NtPathName,
    out const(wchar)* NtFileNamePart, out CurDir DirectoryInfo);

wchar[] toNtPath(const(wchar)[] path)
{
    UnicodeString ntPath;
    CurDir curDir;
    const(wchar)* fileNamePart;
    enforce(RtlDosPathNameToNtPathName_U(path.ptr, ntPath,
        fileNamePart, curDir));
    try
    { return ntPath.Buffer[0 .. ntPath.Length / ntPath.Buffer[0].sizeof].dup; }
    finally { RtlFreeHeap(RtlGetProcessHeap(), 0, ntPath.Buffer); }
}

writeln(toNtPath(r"\\?\C:"));   //Returns the weird string

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Update:

I figured out the problem -- see my answer.

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RtlDosPathNameToNtPathName_U is giving you the correct output. The reason you see a weird-looking character in the middle is because UNICODE_STRINGs are not required to be null-terminated (which I'm sure you know already). The file name \??\C:\ is a completely valid native-format file name. I suspect what you really want is to prepend the device name instead of just referring to the GLOBAL?? directory like what RtlDosPathNameToNtPathName_U has done.

To do that, simply call NtQuerySymbolicLinkObject on \??\x:, where x is the drive letter that the path is using, and prepend the result. If it's a UNC path, prepend \Device\Mup. And so on for the other types of paths (if there are any).

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I figured out the problem myself, with @wj32's help: I'd totally forgotten that the input to RtlDosPathNameToNtPathName_U needed to be null-terminated, and my code didn't handle that properly. Thanks for everyone's help!