C# Signature:
[DllImport("kernel32.dll", SetLastError = true)]
static extern uint QueryDosDevice(string lpDeviceName, IntPtr lpTargetPath, uint ucchMax);
Alternate C# signature:
[DllImport("kernel32.dll", SetLastError = true)]
static extern uint QueryDosDevice(string lpDeviceName, StringBuilder lpTargetPath, int ucchMax);
Alternate C# signature useful for retrieving list of devices
[DllImport("Kernel32.dll")]
static extern uint QueryDosDevice([In, Optional] string lpDeviceName, [Out]byte[] rv, uint ucchMax);
VB.NET Signature:
<DllImport("Kernel32.dll", EntryPoint:="QueryDosDevice")>
Public Shared Function QueryDosDevice(lpDeviceName As String, lpTargetPath As System.Text.StringBuilder, ucchMax As Integer) As Integer
End Function
User-Defined Types:
None.
Notes:
Use the second signature if you want only the current mapping for the DOS device. The first null-terminated string returned by the function contains the current mapping, and will be automatically read into the StringBuilder.
Tips & Tricks:
If you are trying to get a string array of all the Devices on your system, this is the code that I used for this.
Not sure if it's the cleanest... but it works 
VB.NET Sample Code:
' Use the VB.NET signature above with this code. Converting the C#
' signatures will not work.
Private Function QueryDosDevice(ByVal device As String) As List(Of String)
Dim returnSize As Integer = 0
Dim maxSize As UInteger = 65536
Dim allDevices As String = Nothing
Dim mem As IntPtr
Dim retval() As String = Nothing
Dim results As New List(Of String)
' Convert an empty string into Nothing, so
' QueryDosDevice will return everything available.
If device.Trim = "" Then device = Nothing
While returnSize = 0
mem = Marshal.AllocHGlobal(CInt(maxSize))
If mem <> IntPtr.Zero Then
Try
returnSize = CInt(QueryDosDevice(device, mem, maxSize))
If returnSize <> 0 Then
allDevices = Marshal.PtrToStringAuto(mem, returnSize)
retval = allDevices.Split(ControlChars.NullChar)
Exit Try
Else
' This query produced no results. Exit the loop.
returnSize = -1
End If
Finally
Marshal.FreeHGlobal(mem)
End Try
Else
Throw New OutOfMemoryException()
End If
End While
If retval IsNot Nothing Then
For Each result As String In retval
If result.Trim <> "" Then results.Add(result)
Next
End If
Return results
End Function
C# Sample Code:
private static string[] QueryDosDevice()
{
// Allocate some memory to get a list of all system devices.
// Start with a small size and dynamically give more space until we have enough room.
int returnSize = 0;
int maxSize = 100;
string allDevices = null;
IntPtr mem;
string [] retval = null;
while(returnSize == 0)
{
mem = Marshal.AllocHGlobal(maxSize);
if(mem != IntPtr.Zero)
{
// mem points to memory that needs freeing
try
{
returnSize = QueryDosDevice(null, mem, maxSize);
if(returnSize != 0)
{
allDevices = Marshal.PtrToStringAnsi(mem, returnSize);
retval = allDevices.Split('\0');
break; // not really needed, but makes it more clear...
}
else if(GetLastError() == ERROR_INSUFFICIENT_BUFFER)
//maybe better
//else if( Marshal.GetLastWin32Error() == ERROR_INSUFFICIENT_BUFFER)
//ERROR_INSUFFICIENT_BUFFER = 122;
{
maxSize *= 10;
}
else
{
Marshal.ThrowExceptionForHR(GetLastError());
}
}
finally
{
Marshal.FreeHGlobal(mem);
}
}
else
{
throw new OutOfMemoryException();
}
}
return retval;
}
Sample Code for alternate C# signature:
private static string GetRealPath(string path)
{
string realPath;
StringBuilder pathInformation = new StringBuilder(250);
// Get the drive letter of the
string driveLetter = Path.GetPathRoot(path).Replace("\\", "");
QueryDosDevice(driveLetter, pathInformation, 250);
// If drive is substed, the result will be in the format of "\??\C:\RealPath\".
if (pathInformation.ToString().Contains("\\??\\"))
{
// Strip the \??\ prefix.
string realRoot = pathInformation.ToString().Remove(0, 4);
//Combine the paths.
realPath = Path.Combine(realRoot, path.Replace(Path.GetPathRoot(path), ""));
}
else
{
realPath = path;
}
return realPath;
}
Sample C# code retrieving list of devices
public static string[] QueryDevice(string driveLetter=null)
{
byte[] buffer = new byte[4096*32];
uint len = QueryDosDevice(driveLetter, buffer, (uint)buffer.Length);
if (len == 0)
return null;
string rv = ASCIIEncoding.ASCII.GetString(buffer, 0, (int)len-2); // two terminating nulls
return rv.Split("\0".ToCharArray());
}
Alternative Managed API:
Do you know one? Please contribute it!
