I want my WPF app to be able to easily handle long file paths. According to this article, all I have to do is set a registry key and a value in my app manifest. To me this sounds a lot easier than trying to be sure that every file access I do has the \\?\ prefix on it.

But the fact that I need to set this registry key has me wondering: Is there any possible negative effect of setting that registry key? Could other applications be negatively affected?

Because if not, I am left to wonder why Microsoft does not simply enable this for all new installs of Windows. What is the downside?

I want my WPF app to be able to easily handle long file paths. According to this article, all I have to do is set a registry key and a value in my app manifest. To me this sounds a lot easier than trying to be sure that every file access I do has the \\?\ prefix on it.

But the fact that I need to set this registry key has me wondering: Is there any possible negative effect of setting that registry key? Could other applications be negatively affected?

Because if not, I am left to wonder why Microsoft does not simply enable this for all new installs of Windows. What is the downside?

• windows
• filesystems
• long-filenames

• Code written in a language like C is the problem. Lots of such code assumes it can store the path to a file in a char[MAX_PATH]. The buffer overflow caused by long paths is a severe security problem. You might be using such code, even in a WPF app, in a library that you'd never suspect of being dangerous. – Hans Passant Commented 9 hours ago

1 Answer 1

To start off the registry setting you mention is turned on by default in modern Windows. All you need is to turn on long path awareness in your manifest.

Is there any possible negative effect of setting that registry key

Well, it is not backwards compatible, now is it. And the Windows API is trying to be backwards compatible to a fault, even going back to Windows 2.0 for some functions.

This makes functions behave in a different way by accepting different parameters (\\.\ strings), and it introduces the possibility of receiving long paths and sending them to other functions without the prefix, thus breaking the call. You are generally much better off by using the C++ standard library as much as possible, and letting it figure the paths out.