1.10.1 Cannot open UNC paths if longer than 255 characters

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ugo92
Posts: 2
Joined: Mon Mar 02, 2026 9:13 am

1.10.1 Cannot open UNC paths if longer than 255 characters

Post by ugo92 »

XnView: MP 1.10.1 - 64 bit
OS: Windows - 64bit

It looks like the application cannot handle UNC paths longer than 255 characters

Effect: When you try to open files whose path is an UNC path and it's longer than 255 characters, XnView shows an Error dialog with "File not found!" written inside. Shorter file paths are handled just fine.
The difference between a shorter than 255 characters path and a longer than 255 charaters file paths is in the beginning of the path.
The longer one will start with \\?\UNC\server.domain.whatever while the shorter one starts with \\server.domain.whatever


To reproduce:
1. Try to open an image file whose file path is UNC and longer than 255 characters

Actual behaviour (bug): The application cannot find the file

Expected behaviour: The application open the chosen file
jkm
Posts: 402
Joined: Sat May 11, 2024 12:43 am

Re: 1.10.1 Cannot open UNC paths if longer than 255 characters

Post by jkm »

Welcome to the forums...

Please read up on MAX_PATH, a historical limitation in Windows.

https://learn.microsoft.com/en-us/windo ... s=registry

To exceed it, you must explicitly enable LongPaths on your machine, individual applications must opt-in to it, and still not all Windows functions support it.

Have you enabled LongPaths?

Hopefully this sheds some light on what's going on.
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xnview
Author of XnView
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Joined: Mon Oct 13, 2003 7:31 am
Location: France

Re: 1.10.1 Cannot open UNC paths if longer than 255 characters

Post by xnview »

you enter in the pathname filed, a path like \\?\UNC\server.domain.whatever, right?
Pierre.
ugo92
Posts: 2
Joined: Mon Mar 02, 2026 9:13 am

Re: 1.10.1 Cannot open UNC paths if longer than 255 characters

Post by ugo92 »

Thanks for your answers!
Have you enabled LongPaths?
Yes, LongPaths is enabled
you enter in the pathname filed, a path like \\?\UNC\server.domain.whatever, right?
No, i use windows file explorer to reach \\server.domain.whatever\level1\level2\...\levelN\ then i double click image.jpg to open it in XnViewMP.
If i go "deep enough" in the levels the file path becomes longer than 255 characters and the image doesn't open.
I checked its path with right click -> copy as path, that's where I noticed the differences in the beginning of the path
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xnview
Author of XnView
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Joined: Mon Oct 13, 2003 7:31 am
Location: France

Re: 1.10.1 Cannot open UNC paths if longer than 255 characters

Post by xnview »

ugo92 wrote: Wed Mar 04, 2026 8:38 am No, i use windows file explorer to reach \\server.domain.whatever\level1\level2\...\levelN\ then i double click image.jpg to open it in XnViewMP.
If i go "deep enough" in the levels the file path becomes longer than 255 characters and the image doesn't open.
I checked its path with right click -> copy as path, that's where I noticed the differences in the beginning of the path
i've sent you a test version
Pierre.