C# Signature:

[DllImport("Kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
static extern uint GetFinalPathNameByHandle(IntPtr hFile, [MarshalAs(UnmanagedType.LPTStr)] StringBuilder lpszFilePath, uint cchFilePath, uint dwFlags);

User-Defined Types:

private const uint FILE_NAME_NORMALIZED = 0x0;