Any way to work around the PathTooLongException that FileSystemInfo.Fullname throws sometimes?

Question

I have files on my hard drive that throw a PathTooLongException when I access the Fullname property of a FileSystemInfo object. Is there any way around this (excluding renaming the files which is not an option)?

http://msdn.microsoft.com/en-us/library/aa365247%28VS.85%29.aspx#maxpath mentioned by other answers suggests putting a "\?\" prefix on the file name but in this case the DirectoryInfo.GetFileSystemInfos() is responsible for creating the FileSystemInfo objects and DirectoryInfo doesn't accept that prefix so there's no way to use it.

The answer " PathTooLongException in C# code " doesn't help because this is a multi-threaded application and I can't keep changing the current application path.

Do I really have to do everything with PInvoke just to be able to read every file on the hard drive?

Have you tried: http://www.codeproject.com/KB/files/LongFileNames.aspx? — Evan Mulawski, Aug 22 '11 at 21:00

score 5 · Answer 1 · answered May 26 '17 at 23:32

As of Windows 10 (or Windows Server 2016) and .Net 4.6.2, long paths can be supported directly if a registry setting is turned on, and your application is marked as being "long path aware".

The setting can be accessed via the Local Group Policy Editor (gpedit.msc), under Computer Configuration > Administrative Templates > All Settings > Enable Win32 long paths

In order to mark your application as "long path aware", add this section to your manifest file:

<application xmlns="urn:schemas-microsoft-com:asm.v3">
  <windowsSettings>
    <longPathAware xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">true</longPathAware>
  </windowsSettings>
</application>

Additionally, if your application targets a version of the .Net framework earlier than 4.6.2, you'll need to add a section to your App.config file:

<configuration>
  <runtime>
    <AppContextSwitchOverrides value="Switch.System.IO.UseLegacyPathHandling=false;Switch.System.IO.BlockLongPaths=false" />
  </runtime>
</configuration>

For more information see:
https://blogs.msdn.microsoft.com/jeremykuhne/2016/07/30/net-4-6-2-and-long-paths-on-windows-10/ https://msdn.microsoft.com/en-us/library/aa365247(v=vs.85).aspx

(As far as I know, this only affects the basic Windows filesystem APIs. Non-filesystem APIs may still be limited to 260 characters)

I don't think you can set a manifest for ASP.Net applications hosted within IIS. If you're using Asp Core with out-of-process hosting, or running Kestrel standalone or behind a reverse proxy, then I think it should be possible. You can add an "app.manifest" file to your project, same as before, and then you tell the compiler to use it with the setting under Project Properties > Application > Win32 Resources > Manifest. — camerondm9, Mar 24 '22 at 21:24

score 3 · Accepted Answer · answered Aug 22 '11 at 21:54

This looks interesting ... Codeplex Long Path Wrapper

The long path wrapper provides functionality to make it easier to work with paths that are longer than the current 259 character limit of the System.IO namespace. Using the long path classes, projects can now use paths up to 32,000 characters.

I'll give that a try, though I note immediately it doesn't provide an equivalent method to DirectoryInfo.GetFileSystemInfos() so it's going to need some modification.

score 2 · Answer 3 · answered Aug 22 '11 at 21:00

There are not many programs that can survive a path larger than 259 characters. Pretty hard limit for the winapi layer, MAX_PATH is everywhere. It has been considered for .NET but without concrete results. Blog post series ends here with links to previous entries at the bottom.

score 2 · Answer 4 · answered Aug 23 '11 at 07:35

Correctly working with long paths is not that difficult - SetACL does it, for example. But:

the .NET framework classes do not support long paths so you cannot use them
you need to write a wrapper for each file system API function so that it uses the correct long path both for local and UNC paths

Here is the documentation on MSDN about long paths: http://msdn.microsoft.com/en-us/library/aa365247(v=vs.85).aspx

Any way to work around the PathTooLongException that FileSystemInfo.Fullname throws sometimes?

4 Answers4

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