Tuesday, August 16, 2016

.NET 4.6.2–The Long Path edition

While cleaning up my RSS feeds, I noticed a new update of .NET; .NET 4.6.2. Normally I wouldn’t care so much for a minor release but this one caught my attention.

Why? Because the following fix was mentioned; Fix the 269 character file name length limitation. This  has annoyed me for a long time, and I’m happy to see that they finally fixed it. For most of my applications it didn’t matter but I had some file copy tools that got into trouble when folders were nested too deeply.

This new capability is enabled for applications that target the .NET Framework 4.6.2 (or later).

From the announcement:

The following improvements were made to enable long paths:

  • Allow paths that are greater than 260 character (MAX_PATH). Paths that are longer than MAX_PATH are allowed by the BCL. The BCL APIs rely on the underlying Win32 file APIs for limitation checks.
  • Enable extended path syntax and file namespaces (\\?\, \\.\). Windows exposes multiple file namespaces that enable alternate path schemes, such as the extended path syntax, which allows paths to just over 32k characters. The BCL now supports these paths, such as the following: \\?\very long path. The .NET Framework now primarily relies on Windows for path normalization, treating it as the “source of truth”, to avoid inadvertently blocking legitimate paths. The extended path syntax is a good workaround for Windows versions that don’t support long paths using the regular form (for example, `C:\very long path’).
  • Performance Improvements. The adoption of Windows path normalization and the reduction of similar logic in the BCL has resulted in overall performance improvements for logic related to file paths. Other related performance improvements have also been made.

More details on these changes can be found on Jeremy Kuhne’s blog.

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