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How to shorten a path in c# and keep it valid

I work in a place where directories have such a looong name and are in such a looong tree.
And I'm having problems with too long path names for folders in an external applicatoin (I can't change this external application, but I can give it shortened path names).
I know Microsoft operating systems can shorten path names such as transforming C:\TooLongName\TooLongSubDirectory in something like C:\TooLon~1\TooLon~1.
But how can I do this in C# and still keep the nave valid and usable?
PS: I'm not using the standard FileInfo and DirectoryInfo classes, I'm using just strings that will be sent to an external application that I cannot change in any way.

If you are unable to use the long path support build into Windows 10 you are able to use the Win32 command GetShortPathName . In order to generate a suitable path.
class Program
{
[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
static extern uint GetShortPathName(
[MarshalAs(UnmanagedType.LPTStr)]
string lpszLongPath,
[MarshalAs(UnmanagedType.LPTStr)]
StringBuilder lpszShortPath,
uint cchBuffer);
[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
static extern uint GetShortPathName(string lpszLongPath, char[] lpszShortPath, int cchBuffer);
static void Main(string[] args)
{
StringBuilder builder = new StringBuilder(260);
var shortPath = GetShortPathName(#"C:\Projects\Databases\ReallllllllllllllyLOOOOOOOOOOOOOOOOOOOOOONGPATHHHHHHHHHHH\StillllllllllllllllllGOoooooooooooooooooooooooing", builder, (uint)builder.Capacity);
Console.WriteLine(builder.ToString());
Console.ReadKey();
}
}
Produces C:\Projects\DATABA~1\REALLL~1\STILLL~1

How to debug LoadLibraryEx when used from C#

I am trying to load a win32 dll in C# using the LoadLibraryEx.
It is not working - I get a message stating in visual studio "vshost32.exe has stopped working". No exceptions or any clue as to why it doesn't work.
I don't believe it is a dependency problem because if I alter the search paths for the dependencies I get a message box stating "xyz.dll could not be found".
I am wondering if there is a way I can find out why it doesn't load properly. The program stops working on the line:
IntPtr pDll = LoadLibraryEx(#"C:\Program Files\XXX\XXX.dll", IntPtr.Zero, flags);
[UnmanagedFunctionPointer(CallingConvention.StdCall)]
private delegate void ImportResults();
[DllImport("kernel32.dll", SetLastError = true)]
public static extern IntPtr LoadLibraryEx(string dllToLoad, IntPtr hFile, LoadLibraryFlags flags);
[DllImport("kernel32.dll", SetLastError = true)]
public static extern IntPtr GetProcAddress(IntPtr hModule, string procedureName);
[DllImport("kernel32.dll", SetLastError = true)]
public static extern bool FreeLibrary(IntPtr hModule);
[System.Flags]
public enum LoadLibraryFlags : uint
{
DONT_RESOLVE_DLL_REFERENCES = 0x00000001,
LOAD_IGNORE_CODE_AUTHZ_LEVEL = 0x00000010,
LOAD_LIBRARY_AS_DATAFILE = 0x00000002,
LOAD_LIBRARY_AS_DATAFILE_EXCLUSIVE = 0x00000040,
LOAD_LIBRARY_AS_IMAGE_RESOURCE = 0x00000020,
LOAD_WITH_ALTERED_SEARCH_PATH = 0x00000008,
LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR = 0x00000100,
LOAD_LIBRARY_SEARCH_SYSTEM32 = 0x00000800,
LOAD_LIBRARY_SEARCH_DEFAULT_DIRS = 0x00001000
}
public void Import()
{
LoadLibraryFlags flags = LoadLibraryFlags.LOAD_LIBRARY_SEARCH_DEFAULT_DIRS |
LoadLibraryFlags.LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR;
IntPtr pDll = LoadLibraryEx(#"C:\Program Files\XXX\XXX.dll", IntPtr.Zero, flags);
IntPtr pAddressOfFunctionToCall = GetProcAddress(pDll, "ImportResults");
ImportResults import = (ImportResults)Marshal.GetDelegateForFunctionPointer(pAddressOfFunctionToCall,
typeof(ImportResults));
import();
bool result = FreeLibrary(pDll);
}
Update:
I have downloaded the windows sdk and am attempting to use the cdb.exe to debug the problem using the process described here: http://blogs.msdn.com/b/junfeng/archive/2006/11/20/debugging-loadlibrary-failures.aspx
When running the utility I am using this command line:
"C:\Program Files (x86)\Windows Kits\8.1\Debuggers\x86\cdb.exe" loadlib "C:\Program Files\XXX\XXX\XXX.DLL"
But I get this error:
The file definitely exists so I am unsure what I am doing wrong here.

I installed the windows debugging tools: https://msdn.microsoft.com/en-US/windows/desktop/bg162891
I then downloaded the Windows Symbol packages: https://msdn.microsoft.com/en-us/windows/hardware/gg463028.aspx
Then set an environment variable to tell the debugger where to look for symbols:
_NT_SYMBOL_PATH = SRV*C:\dev\symbols*http://msdl.microsoft.com/download/symbols;C:\Symbols
(I installed the symbol package to C:\Symbols)
Then I started my application and attached the debugger with this command:
"C:\Program Files (x86)\Windows Kits\8.1\Debuggers\x86\cdb.exe" -pb -p <pid>
-pb means it won't break on exceptions
-p is the pid of the thread you want to debug
From this I have been able to determine where the error is happening. Still haven't figured out why it's happening though.

WPF application file association: DefaultIcon is not working

I want to association ".abc" file to my WPF application.
I add the association using this code:
public class FileAssociation
{
static RegistryKey Root
{
get
{
return Registry.CurrentUser;
}
}
// Associate file extension with progID, description, icon and application
public static void Associate(string extension,
string progID, string description, string application)
{
Require.NotNullOrEmpty(extension, "extension");
Require.NotNullOrEmpty(progID, "progID");
Require.NotNullOrEmpty(application, "application");
Require.NotNullOrEmpty(description, "description");
Root.CreateSubKey(extension).SetValue("", progID);
using (var key = Root.CreateSubKey(progID))
{
key.SetValue("", description);
key.CreateSubKey("DefaultIcon").SetValue("", ToShortPathName(application).Quote() + ",0");
key.CreateSubKey(#"Shell\Open\Command").SetValue("", ToShortPathName(application).Quote() + " \"%1\"");
// Tell explorer the file association has been changed
SHChangeNotify(0x08000000, 0x0000, IntPtr.Zero, IntPtr.Zero);
}
}
// Return true if extension already associated in registry
public static bool IsAssociated(string extension)
{
return (Root.OpenSubKey(extension, false) != null);
}
[DllImport("shell32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern void SHChangeNotify(uint wEventId, uint uFlags, IntPtr dwItem1, IntPtr dwItem2);
[DllImport("Kernel32.dll")]
private static extern uint GetShortPathName(string lpszLongPath,
[Out] StringBuilder lpszShortPath, uint cchBuffer);
// Return short path format of a file name
private static string ToShortPathName(string longName)
{
StringBuilder s = new StringBuilder(1000);
uint iSize = (uint)s.Capacity;
uint iRet = GetShortPathName(longName, s, iSize);
return s.ToString();
}
}
Note: The Quote() extension method is used just to make string abc to "abc".
Now the file association works fine! I can double click the ".abc" files to open my WPF app.
But the DefaultIcon is not working. The DefaultIcon Registery key is set to "D:\path\to\MyWPFApp.exe",0. The application icon of my WPF app is set to an icon in the properties page (I can see that the icon of MyWPFApp.exe is already changed). What's wrong? Thanks!
BTW: I'm using .NET 4 in Windows 8

You don't need the DefaultIcon entry. The first icon is used by default.
remove it and it should work ^^
If I remove the ToShortPathName (long name is ok with quotes) and
change the Root property returns Registry.ClassesRoot the code works here.

How to open text in Notepad from .NET?

When I click a button on a Windows Forms form, I would like to open a Notepad window containing the text from a TextBox control on the form.
How can I do that?

You don't need to create file with this string. You can use P/Invoke to solve your problem.
Usage of NotepadHelper class:
NotepadHelper.ShowMessage("My message...", "My Title");
NotepadHelper class code:
using System;
using System.Runtime.InteropServices;
using System.Diagnostics;
namespace Notepad
{
public static class NotepadHelper
{
[DllImport("user32.dll", EntryPoint = "SetWindowText")]
private static extern int SetWindowText(IntPtr hWnd, string text);
[DllImport("user32.dll", EntryPoint = "FindWindowEx")]
private static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);
[DllImport("User32.dll", EntryPoint = "SendMessage")]
private static extern int SendMessage(IntPtr hWnd, int uMsg, int wParam, string lParam);
public static void ShowMessage(string message = null, string title = null)
{
Process notepad = Process.Start(new ProcessStartInfo("notepad.exe"));
if (notepad != null)
{
notepad.WaitForInputIdle();
if (!string.IsNullOrEmpty(title))
SetWindowText(notepad.MainWindowHandle, title);
if (!string.IsNullOrEmpty(message))
{
IntPtr child = FindWindowEx(notepad.MainWindowHandle, new IntPtr(0), "Edit", null);
SendMessage(child, 0x000C, 0, message);
}
}
}
}
}
References (pinvoke.net and msdn.microsoft.com):
SetWindowText: pinvoke | msdn
FindWindowEx: pinvoke | msdn
SendMessage: pinvoke | msdn

Try this out:
System.IO.File.WriteAllText(#"C:\test.txt", textBox.Text);
System.Diagnostics.Process.Start(#"C:\test.txt");

Save the file to disk using File.WriteAllText:
File.WriteAllText("path to text file", myTextBox.Text);
Then use Process.Start to open it in notepad:
Process.Start("path to notepad.exe", "path to text file");

For non ASCII user.
[DllImport("User32.dll", EntryPoint = "SendMessage", CharSet = CharSet.Unicode)]
private static extern int SendMessage(IntPtr hWnd, int uMsg, int wParam, string lParam);
Based on #Peter Mortensen answer
Add CharSet = CharSet.Unicode to the attribute for supporting Unicode characters

I was using the NotepadHelper solution until I discovered it doesn't work on Windows 11. Writing the file to disk and starting with the default text editor seems to be the best solution. This has already been posted, but I discovered you need to pass UseShellExecute=true.
System.IO.File.WriteAllText(path, value);
System.Diagnostics.ProcessStartInfo psi = new() { FileName = path, UseShellExecute = true };
System.Diagnostics.Process.Start(psi);
I write to the System.IO.Path.GetTempPath() folder and run a cleanup when the application exits - searching for a unique prefix pattern for file names used by my app. Something like this:
string pattern = TempFilePrefix + "*.txt";
foreach (string f in Directory.EnumerateFiles(Path.GetTempPath(), pattern))
{
File.Delete(f);
}

The best way to resolve display username by SID?

I read a list of SIDs from the registry, HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList.
How would one resolve the display username (e.g. DOMAIN\user, BUILT-IN\user) given the SID string in C#?

Just found it on the pinvoke.net.
Alternative Managed API:
Available in .Net 2.0:
using System.Security.Principal;
// convert the user sid to a domain\name
string account = new SecurityIdentifier(stringSid).Translate(typeof(NTAccount)).ToString();

The Win32 API function LookupAccountSid() is used to find the name that corresponds to a SID.
LookupAccountSid() has the following signature:
BOOL LookupAccountSid(LPCTSTR lpSystemName, PSID Sid,LPTSTR Name, LPDWORD cbName,
LPTSTR ReferencedDomainName, LPDWORD cbReferencedDomainName,
PSID_NAME_USE peUse);
MSDN Ref.
Here's the P/Invoke reference (with sample code): http://www.pinvoke.net/default.aspx/advapi32.LookupAccountSid
[DllImport("advapi32.dll", CharSet=CharSet.Auto, SetLastError = true)]
static extern bool LookupAccountSid (
string lpSystemName,
[MarshalAs(UnmanagedType.LPArray)] byte[] Sid,
StringBuilder lpName,
ref uint cchName,
StringBuilder ReferencedDomainName,
ref uint cchReferencedDomainName,
out SID_NAME_USE peUse);