Search
Module:
Directory

   Desktop Functions:

   Smart Device Functions:


Show Recent Changes
Subscribe (RSS)
Misc. Pages
Comments
FAQ
Helpful Tools
Playground
Suggested Reading
Website TODO List
Support Forum
Download Visual Studio Add-In

Terms of Use
Privacy Policy
querydosdevice (kernel32)
 
.
Summary

C# Signature:

[DllImport("kernel32.dll")]
static extern uint QueryDosDevice(string lpDeviceName, IntPtr lpTargetPath,
   uint ucchMax);

Alternate C# signature:

[DllImport("kernel32.dll")]
static extern uint QueryDosDevice(string lpDeviceName, StringBuilder lpTargetPath, int ucchMax);

VB.NET Signature:

Private Declare Auto Function QueryDosDevice Lib "kernel32.dll" (ByVal lpDeviceName As String, _
                                     ByVal lpTargetPath As IntPtr, _
                                     ByVal ucchMax As UInteger) As UInteger

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;
}

Alternative Managed API:

Do you know one? Please contribute it!

Documentation

Please edit this page!

Do you have...

  • helpful tips or sample code to share for using this API in managed code?
  • corrections to the existing content?
  • variations of the signature you want to share?
  • additional languages you want to include?

Select "Edit This Page" on the right hand toolbar and edit it! Or add new pages containing supporting types needed for this API (structures, delegates, and more).

 
Access PInvoke.net directly from VS:
Terms of Use
Edit This Page
Find References
Show Printable Version
Revisions