Why does the 260 character path length limit exist in Windows?

Question

I have come up against this problem a few times at inopportune moments:

• Trying to work on open source Java projects with deep paths
• Storing deep Fitne

Answer 1

This is not strictly true as the NTFS filesystem supports paths up to 32k characters. You can use the win32 api and "\\?\" prefix the path to use greater than 260 characters.

A detailed explanation of long path from the .Net BCL team blog.
A small excerpt highlights the issue with long paths

Another concern is inconsistent behavior that would result by exposing long path support. Long paths with the \\?\ prefix can be used in most of the file-related Windows APIs, but not all Windows APIs. For example, LoadLibrary, which maps a module into the address of the calling process, fails if the file name is longer than MAX_PATH. So this means MoveFile will let you move a DLL to a location such that its path is longer than 260 characters, but when you try to load the DLL, it would fail. There are similar examples throughout the Windows APIs; some workarounds exist, but they are on a case-by-case basis.

Answer 2

As to why this still exists - MS doesn't consider it a priority, and values backwards compatibility over advancing their OS (at least in this instance).

A workaround I use is to use the "short names" for the directories in the path, instead of their standard, human-readable versions. So e.g. for C:\Program Files\ I would use C:\PROGRA~1\ You can find the short name equivalents using dir /x.

Answer 3

Another way to cope with it is to use Cygwin, depending on what do you want to do with the files (i.e. if Cygwin commands suit your needs)

For example it allows to copy, move or rename files that even Windows Explorer can't. Or of course deal with the contents of them like md5sum, grep, gzip, etc.

Also for programs that you are coding, you could link them to the Cygwin DLL and it would enable them to use long paths (I haven't tested this though)

Answer 4

From Windows 10. you can remove the limitation by modifying a registry key.

Tip Starting in Windows 10, version 1607, MAX_PATH limitations have been removed from common Win32 file and directory functions. However, you must opt-in to the new behavior.

A registry key allows you to enable or disable the new long path behavior. To enable long path behavior set the registry key at HKLM\SYSTEM\CurrentControlSet\Control\FileSystem LongPathsEnabled (Type: REG_DWORD). The key's value will be cached by the system (per process) after the first call to an affected Win32 file or directory function (list follows). The registry key will not be reloaded during the lifetime of the process. In order for all apps on the system to recognize the value of the key, a reboot might be required because some processes may have started before the key was set. The registry key can also be controlled via Group Policy at Computer Configuration > Administrative Templates > System > Filesystem > Enable NTFS long paths. You can also enable the new long path behavior per app via the manifest:

<application xmlns="urn:schemas-microsoft-com:asm.v3">
    <windowsSettings xmlns:ws2="http://schemas.microsoft.com/SMI/2016/WindowsSettings">
        <ws2:longPathAware>true</ws2:longPathAware>
    </windowsSettings>
</application>

Answer 5

It does, and it is a default for some reason, but you could easily override it with this registry key:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem]
"LongPathsEnabled"=dword:00000001

See: https://blogs.msdn.microsoft.com/jeremykuhne/2016/07/30/net-4-6-2-and-long-paths-on-windows-10/

Answer 6

The question is why does the limitation still exist. Surely modern Windows can increase the side of MAX_PATH to allow longer paths. Why has the limitation not been removed?

• The reason it cannot be removed is that Windows promised it would never change.

Through API contract, Windows has guaranteed all applications that the standard file APIs will never return a path longer than 260 characters.

Consider the following correct code:

WIN32_FIND_DATA findData;

FindFirstFile("C:\Contoso\*", ref findData);

Windows guaranteed my program that it would populate my WIN32_FIND_DATA structure:

WIN32_FIND_DATA {
   DWORD    dwFileAttributes;
   FILETIME ftCreationTime;
   FILETIME ftLastAccessTime;
   FILETIME ftLastWriteTime;
   //...
   TCHAR    cFileName[MAX_PATH];
   //..
}

My application didn't declare the value of the constant MAX_PATH, the Windows API did. My application used that defined value.

My structure is correctly defined, and only allocates 592 bytes total. That means that i am only able to receive a filename that is less than 260 characters. Windows promised me that if i wrote my application correctly, my application would continue to work in the future.

If Windows were to allow filenames longer than 260 characters then my existing application (which used the correct API correctly) would fail.

For anyone calling for Microsoft to change the MAX_PATH constant, they first need to ensure that no existing application fails. For example, i still own and use a Windows application that was written to run on Windows 3.11. It still runs on 64-bit Windows 10. That is what backwards compatibility gets you.

Microsoft did create a way to use the full 32,768 path names; but they had to create a new API contract to do it. For one, you should use the Shell API to enumerate files (as not all files exist on a hard drive or network share).

But they also have to not break existing user applications. The vast majority of applications do not use the shell api for file work. Everyone just calls FindFirstFile/FindNextFile and calls it a day.